Process reactive gases

Catalysis By definition, a catalyst is a substance (in this book a solid) which can accelerate the approach of a reactive gas mixture to equilibrium, without itself being consumed in this process. 

Example 11.7 hints at the complications that are possible in reactive gas absorption. Gas absorption is an important unit operation that has been the subject of extensive research and development. Large, proprietary computer codes are available for purchase, and process simulation tools such as Aspen can do the job. However, as shown in Example 11.8, simple but useful approximations are sometimes possible. 

Colorless, reactive gas. Oxygen was not present in the initial atmosphere of the Earth, although at 50 % it is the most common element in the crust of the Earth (oxides, silicates, carbonates, etc.). The compound with hydrogen is remarkable. The hydrides of all other elements are unpleasant compounds, but H20 is the molecule of life. The 02 found in the air today, of which it makes up 20 %, was formed in the process of evolution by photosynthesis of algae, which then also allowed life on solid land. Oxidation with oxygen became and is still the dominant pathway of life forms for obtaining energy (respiration). Used in medicine in critical situations. Oxidations play a key role in chemistry (sulfuric acid, nitric acid, acetic acid, ethylene oxide, etc.). The ozone layer in space protects the Earth from cosmic UV radiation. Ozone (03) is used in the... 

In the RSDT process, the steps for infroducing cafalysf, ionomer, and carbon into the gas mix are decoupled and can be independently controlled in such a manner that the Pt/C and ionomer/C ratios can be continuously modified during fhe deposition process. Reactive spray deposition technology has the capacity and flexibility required to produce compositionally and... 

Char oxidation dominates the time required for complete burnout of a coal particle. The heterogeneous reactions responsible for char oxidation are much slower than the devolatilization process and gas-phase reaction of the volatiles. Char burnout may require from 30 ms to over 1 s, depending on combustion conditions (oxygen level, temperature), and char particle size and reactivity. Char reactivity depends on parent coal type. The rate-limiting step in char burnout can be chemical reaction or gaseous diffusion. At low temperatures or for very large particles, chemical reaction is the rate-limiting step. At... 

Finally, autocatalytic processes, which do not involve the use of a reactive gas can occur when appropriate ligands are introduced in the metal precursor. Thus, pure ruthenium films, with only 3mol.% carbon content, have been deposited... 

Ullrafine particles (UFPs) of metal and semiconductor nitrides have been synthesized by two major techniques one is the reactive gas condensation method, and the other is the chemical vapor condensation method. The former is modified from the so-called gas condensation method (or gas-evaporation method) (13), and a surrounding gas such as N2 or NII2 is used in the evaporation chamber instead of inert gases. Plasma generation has been widely adopted in order to enhance the nitridation in the particle formation process. The latter is based on the decomposition and the subsequent chemical reaction of metal chloride, carbonate, hydride, and organics used as raw materials in an appropriate reactive gas under an energetic environment formed mainly by thermal healing, radiofrequency (RF) plasma, and laser beam. Synthesis techniques are listed for every heal source for the reactive gas condensation method and for the chemical vapor condensation method in Tables 8.1.1 and 8.1.2, respectively. 

The sampling atmosphere is an important factor. The sampling atmosphere may be an inert gas, or reactive gas or vacuum. When a gas is used, the atmosphere can either be flowing through the measurement chamber or static (i.e. nonflowing). If the atmosphere is static, the decomposition products may remain in the area of the sample and cause secondary reactions to occur, which are not necessarily related to the heating process. 

In a practical HDS process for gas oil, both aromatic species existing in the feed and various types of sulfur compounds compete for the active sites on the catalyst surface. Moreover, H2S and some other hydrocarbons produced in the early stages of the desulfurization appear to inhibit the HDS of the less reactive sulfur species. The reactivities of refractory sulfur compounds and the effects of inhibitors in gas oils need to be fully understood for the development of an improved economical desulfurization process. 

Chemical vapor deposition. Chemical vapor deposition is mainly used to prepare thin films and coatings, and infrequently, supported particles.68,69 The films are formed by the chemical reaction of a gas phase species with the heated surface of a substrate. The process can be assisted by a reactive gas like NH3, a plasma,7a 72 ultraviolet73,74 or laser75 radiation. 

The sequence of operations (assuming the initial solid is not air sensitive) would be to load the sample tube with a weighed amount of reactive compound and the stirrer, to attach this tube to the tensimeter, and to pump out the air in the tensimeter. The sample tube is cooled to liquid nitrogen temperature and solvent is then condensed into the sample tube from a storage container on the vacuum line. The main valve on the tensimeter is then closed and the sample container allowed to warm so the solid may dissolve, perhaps with the aid of the stirrer. A constant temperature slush bath is next placed around the sample tube as illustrated in Fig. 9.5 and an initial pressure measurement is taken on the manometer. Next, the first alloquot of the reactive gas is transferred from a storage bulb elsewhere on the vacuum system into the calibrated bulb using the techniques outlined in Section 5.3.G (the bubbler manometer shown in Fig. 9.5 is used for the pressure determination required for this process). This gas is con-... 

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