Precipitation from a gas

For hydrogen oxidation bi-component metal doped systems deposited on Raney nickel for AFC Mo and W carbides for AFC prepared by method of precipitation from a gas phase Radicals of following composition -OH, -OSO3H, -COOH, -OPO(OH)3 for PEMFC Some organic catalysts like biologically active [NiFe]-hydrogenase, pyropolymers, etc. ... 

Free-Running Deposits. The composition (as regards particle size) and quantity of free-running deposits precipitated from a gas flow depends on the size distribution and concentration of the particles in the flow, the operating time of the plant, the velocity and direction of the flow, and also the diameter and mutual arrangement of the pipes. 

Polymers that form from the liqmd phase may remain dissolved in the remaining monomer or solvent, or they may precipitate. Sometimes beads are formed and remain in suspension sometimes emulsions form. In some processes solid polymers precipitate from a fluidized gas phase. 

Other lesser mechanisms that result in aerosol removal by filters are (1) gravitational settling due to the difference in mass of the aerosol and the carrying gas, (2) thermal precipitation due to the temperature gradient between a hot gas stream and the cooler filter medium which causes the particles to be bombarded more vigorously by the gas molecules on the side away from the filter element, and (3) Brownian deposition as the particles are bombarded with gas molecules that may cause enough movement to permit the aerosol to come in contact with the filter element. Browruan motion may also cause some of the particles to miss the filter element because they are moved away from it as they pass by. For practical purposes, only the three mechanisms shown in Fig. 29-1 are normally considered for removal of aerosols from a gas stream. 

Electronic air cleaner A device used to clean particulate matter from a gas stream, consisting of a fan and an electrostatic precipitator. 

Precipitator, electrostatic A device for collecting particulate matter from a gas stream by using electric forces to impart a negative charge to the particulate matter in the gas stream. These charged particulates are attracted to collecting surfaces which have the opposite polarity. 

If the temperature and supersaturation are sufficiently high in a CVD reaction, the product is primarily powder precipitated from the gas phase (see Ch. 2). Such powders have few impurities provided that the CVD precursors are carefully purified. Their small diameter and great uniformity are important factors in the production of high quality hot-pressed or sintered ceramic bodies with good mechanical and electrical properties. In addition, the sintering temperatures required for CVD powders are lower than those for conventional powders. 

Electrostatic precipitators are generally used to separate particulate matter that is easily ionized from a gas stream3,8,10. This is accomplished by an electrostatic field produced between wires or grids and collection plates by... 

In the last of these reactions, Ca2+ has a higher charge than H+, but it is also much larger. Although the predictions are correct for a very large number of cases, the removal of a product from the reaction zone (formation of a precipitate or a gas) can cause the system to behave differently. 

Although gallium sulfide does not precipitate from a solution of the pure salt, it is readily carried down with zinc sulfide. Boisbaudran therefore added ammonium acetate and acetic acid to the hydrochloric acid solution of the above precipitate, and passed in hydrogen sulfide. As long as the line Ga a (417 0) continued to show in the spectrum of the precipitate, he kept on adding zinc to the filtrate until finally all the gallium had been precipitated. 

Electrostatic Precipitation. It may be defined as " the use of an electrostatic field for precipitating or rapidly removing solid or liquid particles from a gas in which the particles are carried in suspension ... 

Additional Exercises Lead chromate, PbC rO, calcium phosphate, Ca3(PC>4)2 ferrous oxalate, Fe(C2C>4) sodium chloride, NaCl, precipitated from a saturated solution by HC1 gas, Richards and Wells, Revision of the atomic weights of sodium and chlorine, J. Am. Chem. Soc., 27, 459 (1905). 

Cottrel s trap an electrostatic precipitator for removing dust from a gas stream... 

Removal of sulfur dioxide from a gas stream. If a fuel that contains sulfur is burned, the product gas contains sulfur dioxide. If the gas is released directly into the atmosphere, the SO2 combines with atmospheric oxygen to form sulfur trioxide. The SO3 in turn combines with water vapor in the atmosphere to form sulfuric acid (H7SO4), which eventually precipitates as acid rain. To prevent this occurrence, the combustion product gas is contacted with a liquid solution in an absorption or scrubbing process. The SO2 dissolves in the solvent and the clean gas that remains is released to the atmosphere. 

Polymerization can be catalytic or noncatalytic, and can be homogeneously or heterogeneously catalyzed. Polymers that form from the liquid phase may remain dissolved in the remaining monomer or solvent, or they may precipitate. Sometimes beads are formed and remain in suspension sometimes emulsions form. In some processes solid polymers precipitate from a fluidized gas phase. Polymerization processes are also characterized by extremes in temperature, viscosity, and reaction times. For instance, many industrial polymers are mixtures with molecular weights of 104 to 107. In polymerization of styrene the viscosity increased by a factor of 106 as conversion increased from 0 to 60 percent. The adiabatic reaction temperature for complete polymerization of ethylene is 1800 K (3240°R). Initiators of the chain reactions have concentration as low as 10-8 g-moFL, so they are highly sensitive to small concentrations of poisons and impurities. 

An electrostatic precipitator (ESP) is being used to clean fly ash from a gas. The precipitator contains 30 ducts, with plates 12 ft high and 12 ft long. The spacing between the plates is 8 in. The gas is evenly distributed through all of the ducts. The following information can be used ... 

It is well known that a process of gas dissolution and precipitation from a melt has its origins in diffusion of atoms to the gas-liquid interface. So we should take into consideration not only the thermodynamic conditions of gas transition from a solution but the kinetic conditions, particularly an amount of degassing centers, as well. 

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