Impurities in the Gas

The gas plant products, namely fuel gas, Cfs, 4, and gasoline, contain sulfur compounds that require treatment. Impurities in the gas plant products are acidic in nature. Examples include hydrogen sulfide (HjS), carbon dioxide (COj), mercaptan (R-SH), phenol (ArOH), and naphthenic acids (R-COOH). Carbonyl and elemental sulfur may also be present in the above streams. These compounds are acidic. 

The ion yields of 02+ arising from 3.3 X 10 2 mole % oxygen impurity in the gas are not shown since its contribution at maximum pressure is less than 3%. % Ion yield refers to % total ions observed... 

Gettering. Gettering materials, such as zirconium or titanium alloys, are heated to 400°C. At that temperature, they react with the impurities in the gas stream such as O2, H2O, N2, H2, CO, CO2, and hydrocarbons. Total impurities can be reduced to <100 ppb. 

Another difference between Co and Fe is their sensitivity towards impurities in the gas feed, such as H2S. In this respect, Fe-based catalysts have been shown to be more sulfur-resistance than their Co-based counterparts. This is also the reason why for Co F-T catalysts it is recommended to use a sulphur-free gas feed. For this purpose, a zinc oxide bed is included prior to the fixed bed reactor in the Shell plant in Malaysia to guarantee effective sulphur removal. Co and Fe F-T catalysts also differ in their stability. For instance, Co-based F-T systems are known to be more resistant towards oxidation and more stable against deactivation by water, an important by-product of the FTS reaction (reaction (1)). Nevertheless, the oxidation of cobalt with the product water has been postulated to be a major cause for deactivation of supported cobalt catalysts. Although, the oxidation of bulk metallic cobalt is (under realistic F-T conditions) not feasible, small cobalt nanoparticles could be prone to such reoxidation processes. 

The oxidation behaviour of Si3N4 ceramics strongly depends on impurities in the gas atmosphere. Impurities like alkaline or alkaline earth metals, S02, and vanadium drastically decrease oxidation [431, 433, 434]. The main influence of the different impurities is caused by a change of the viscosity or the destruction of the oxide scale, accelerating the diffusion of oxygen or water vapour into the ceramic and increasing the corrosion. Of coarse, the effect strongly depends on temperature and gas composition. 

Monoethanolamine is the oldest and probably still the most widely used solvent (Fig. 1). For desulfurization of natural gas, a 10 to 30% aqueous solution of monoethanolamine is normally used and a variety of solvents are available that vary in solvent selectivity for absorption of hydrogen sulfide and carbon dioxide, and this property, as well as the composition of the impurities in the gas being treated, frequently determines the choice of solvent. Some of... 

One of the greatest difficulties in making surface tension measurements is ensuring the purity of the substance studied. Minute amounts of impurity, by concentrating at the surface, can make an appreciable difference in measured surface properties. Small amounts of reactive or condensable impurities in the gas phase can also greatly influence measured surface tensions. 

The inner surface of hydrogen gas vessels is susceptible to localized corrosion due to impurities that can exist in the steel and hydrogen gas." Interactions between localized corrosion and hydrogen embrittlement have not been specified however, impurities in the gas and steel are known to affect hydrogen embrittlement, as described in section 7.4. 

Contradictory data on the kinetics of ammonia synthesis, especially in the earlier literature, in some circumstances may reflect a lack of attention to the influence of impurities in the gas. If oxygen compounds are present in the synthesis gas, reversible poisoning of the adsorbing areas, in accordance with an equilibrium depending on the temperature and the water vapor-hydrogen partial pressure ratio, must be taken into account when developing rate equations (see also Section 3.6.1.5). 

Little work has been done on the free radical chemistry of NO binding to transition metals. Careful removal of impurities in the gas stream and absence of nitrite and/or N02 in solution must be ensured.96 For the general reaction described by Equation (12),... 

The coalescer absorbs fine aerosol contaminants, such as water vapor and particulates, and thus removes finer impurities in the gas stream that are not wanted in the final product. 

The process is quite sensitive to small amounts of impurities in the gas stream, particularly oxygen and moisture. 

Impurities in the gas (oil, water, oxygen, hydrocarbons) cause baseline problems. 

Another major consideration in the design of the plant is the nature and quantity of impurities in the gas stream delivered to the acid plant. No acid plant can operate satisfactorily with an inadequate gas purification section. The gas will normally be delivered to the acid plant at about 600°F after most of the dust has been removed in electrostatic precipitators. However, the gas may still contain dust, as well as sulfur trioxide, halogens, arsenic, and other metallic vapors. 

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