High-temperature vapor-phase treatment

Demetallation of Heteroatom Zeolites through High-temperature Vapor-phase Treatment... 

Example on Preparation of Cyclopentadiene. Cyclopentadiene is obtained in high-temperature vapor-phase petroleum cracking operations. It is mixed with other hydrocarbons, and its separation is complicated by the fact that it will dimerize and the dimer will depolymerize at about normal distillation conditions. One method of operating is to dimerize the pentadiene and then remove all remaining constituents below C7. The residue is then given a thermal treatment which will depolymerize the dimer, and the mixture is distilled to obtain the cyclopentadiene. A unit is to be designed for this final fractional distillation, and an estimate is to be made of the amount of polymerization that will be obtained. 

Very recently, zeolites have also been modified by chlorine (13) and chlorine-related compounds at high temperature (14, 15). The known modification methods can be further classified as either liquid or vapor phase treatments. The acid washing, organic complexing agent extraction and chromic salt treatments fall into the first class while the steaming and the chlorine and related compounds reactions belong to the second class. 

The most intensive development of the nanoparticle area concerns the synthesis of metal particles for applications in physics or in micro/nano-electronics generally. Besides the use of physical techniques such as atom evaporation, synthetic techniques based on salt reduction or compound precipitation (oxides, sulfides, selenides, etc.) have been developed, and associated, in general, to a kinetic control of the reaction using high temperatures, slow addition of reactants, or use of micelles as nanoreactors [15-20]. Organometallic compounds have also previously been used as material precursors in high temperature decomposition processes, for example in chemical vapor deposition [21]. Metal carbonyls have been widely used as precursors of metals either in the gas phase (OMCVD for the deposition of films or nanoparticles) or in solution for the synthesis after thermal treatment [22], UV irradiation or sonolysis [23,24] of fine powders or metal nanoparticles. 

Thermal treatment—Processes in which vapor-phase contaminants are destroyed via high-temperature oxidation the primary categories of thermal treatment used to treat MTBE and other oxygenates include thermal oxidation, which employs a flame to generate the high temperatures needed to oxidize contaminants, and catalytic oxidation, which employs lower temperatures in the presence of a catalyst (typically platinum, palladium, or other metal oxides) to destroy contaminants. 

Much of the theory of scaling analysis was developed for molecular beam epitaxy (MBE), and there are some challenges in transferring the treatment to electrodeposition. In MBE, the incident atoms originate at a source at high temperature, arrive at the growth front from a vapor phase that is not in internal equilibrium, attach... 

Table 13.1). In the solid P(CH4) > P(CD4) but the curves cross below the melting point and the vapor pressure IE for the liquids is inverse (Pd > Ph). For water and methane Tc > Tc, but for water Pc > Pc and for methane Pc < Pc- As always, the primes designate the lighter isotopomer. At LV coexistence pliq(D20) < Pliq(H20) at all temperatures (remember the p s are molar, not mass, densities). For methane pliq(CD4) < pLiq(CH4) only at high temperature. At lower temperatures Pliq(CH4) < pliq(CD4). The critical density of H20 is greater than D20, but for methane pc(CH4) < pc(CD4). Isotope effects are large in the hydrogen and helium systems and pLIQ/ < pLiQ and P > P across the liquid range. Pc < Pc and pc < pc for both pairs. Vapor pressure and molar volume IE s are discussed in the context of the statistical theory of isotope effects in condensed phases in Chapters 5 and 12, respectively. The CS treatment in this chapter offers an alternative description.

Treatments favouring contact between solid and liquid phases such as pumping over or punching down are traditionally used to enhance extraction. Alternative processes have been proposed more recently. These include physical processes such as thermoviniflcation and flash release (in which the grapes are heated quickly at high temperature (> 95°C) and then placed under vacuum, to produce instant vaporization and cooling) and the use of pectinolytic enzymes. 

The catalyst slowly deactivated during the cyclic operation and, after an extended period (two to four weeks), olefin breakthrough occurred during an alkylation cycle. At this point, the catalyst activity was fully restored by treatment with vapor phase H2 at 250 °C, as described previously. Even after this high temperature regeneration (FITR) procedure was carried out 15 times during a pilot run of more than six months with the same catalyst sample, catalyst activity could be fully recovered. A coke burn with air was not required. 

The catalytic fluorodecarboxylation of arylchloroformate to fluorobenzene and analogues has been achieved with high yield in an anhydrous hydrogen fluoride vapor phase flow reactor. This methodology can be successfully applied to various derivates, the main limitation being the stability of substituents under the reaction conditions. The best catalysts are chromium and aluminium oxyfluoride. The reaction proceeds between 300 and 400°C and occurs in a short space of time. The catalytic activity decreases by coking but can be fully recovered by an oxydative treatment at high temperature. An ionic mechanism is proposed. 

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