Gases containing contaminants

In applications where Nafion is not suitable, at temperatures above 200 °C with feed gas heavily contaminated with CO and sulfur species, a phosphoric acid fuel cell (PAFC)-based concentrator has been effective [15]. Treating the gas shown in Table 1, a H2 product containing 0.2% CO, 0.5%CO2 and only 6 ppm H2S was produced. The anode electrode was formed from a catalyst consisting basically of Pt-alloy mixed with 50% PTFE on a support of Vulcan XC-72 carbon. The cathode was... 

Gas phase oxidation is commonly used for the purification of CNTs. The method proposed by Ebbesen et al. [20] uses heat treatment of crude CNT products under a gas containing oxygen. This method has been explored extensively because it can yield the most highly graphitized tubes without being contaminated by the metal catalyst. 

The capture of C02 from process streams has been performed already for some decades in various industries. Examples of the capture of C02 from industrial applications are the production of hydrogen-containing synthesis gas for the production of ammonia or synthetic fuels or the purification of natural gas (from contaminated gas fields). Since in these processes, C02 is usually considered an undesired by-product, it is then released into the atmosphere. 

Off-gas from the coke burner ( -Gas) contains nitrogen, sulphur dioxide (SO2), hydrogen sulphide (H2S), carbon monoxide (CO), carbon dioxide (CO2), water vapour and other trace contaminants. The -Gas is directed to the CO Boiler for incineration where sulphur compounds are converted to SO2. The Boiler flue gas is passed through electrostatic precipitators for particulate control and then emission to atmosphere. The CO Boiler also serves as the Sulphur Plant tail gas incinerator. Maximum sulphur emissions are 146 tonnes/day or 10.6% of sulphur contained in bitumen feed to the cokers. 

Propylene oxide in the amount of 5000 tons/yr will be made by the chlorohydrin process. The basic feed material is a hydrocarbon mixture containing 90% propylene and the balance propane which does not react. This material is diluted with spent gas from the process to provide a net feed to chlorination which contains 40 mol % propylene. Chlorine gas contains 3% each of air and carbon dioxide as contaminants. 

Metal Contaminants and Ash. Alkali metals form basic oxides that are very reactive toward acidic species such as the acid gases, silicates, and aluminates. These form stable salts with acid gases if the off-gas contains such gases. Sodium, the most common of these metals, prefers to form chlorides ahead of sulfates. Sodium carbonate only forms in the absence of halides and sulfur oxides, SO. There usually is too litde NO present to form... 

The liquid carbon dioxide absorbent, with sulfurous compounds, other trace contaminants, and perhaps some co-absorbed light hydrocarbons such as methane and ethane, is combined with the contaminated liquid carbon dioxide condensed in precooling to -55°C. The combined carbon dioxide stream, typically 3 to 5 mol % hydrogen sulfide, is stripped of light hydrocarbons if necessary, and sent to the carbon dioxide regenerator. The treated gas, containing less than 1 ppm H2S, leaves the sulfur absorber at essentially -55°C with carbon dioxide the only significant impurity yet to be removed. 

In the actual process (Figure 10-5), the natural gas feedstock must first be desulfurized in order to prevent catalyst poisoning or deactivation. The desulfurization step depends upon the nature of the sulfur-containing contaminants and can vary from the more simple ambient temperature adsorption of the sulfur-containing materials on activated charcoal to a more complex high-temperature reaction with zinc oxide to catalytic hydrogenation followed by zinc oxide treatment. 

The manufacturer of the prepolymer endeavors to supply a low-moisture, low-free isocyanate, gas-free material. Moisture may be introduced with repeated opening of the prepolymer container. Contaminants will form bubbles in the final material. Any moisture or free isocyanates will have an effect on the reaction ratios as well as change the chemistry to a degree. 

Alkaline, alkaline earth metals and aluminum are naturally covered with anodic films. The removal of these native films, even in the best glove box atmosphere, exposes the fresh metal to reactive atmospheric contaminants at a high enough concentration and quickly cover the metal with new surface films. As discussed above, even the glove box atmosphere of an inert gas containing atmospheric components at the ppm level should be considered as being quite reactive to active metals such as lithium. Therefore, anyone intending to study the intrinsic behavior of active metal electrodes in solution must prepare a fresh electrode surface in solution. 

Filling chambers A and B with gas should be done with care. If a simple reducing valve is used, the high-pressure valve on the storage cylinder should never be opened when gas is being admitted to the system. Allow the gas contained in the section between the two valves to expand into the chamber then close the needle valve and refill this section. Repeat this procedure several times (if necessary) until the chamber is full. Flushing the chamber once or twice with the appropriate gas will reduce the possibility of contamination. 

Natural gas is largely made up of methane but also contains other light hydrocarbons, typically ethane through hexane. In addition, natural gas contains inorganic contaminants - notably hydrogen sulfide and carbon dioxide, but also nitrogen and trace amounts of helium and hydrogen. 

---