Chemical temperature range selection

We present results for two standard tin oxide precursors, DMTC and MBTC, as well as for tin tetrachloride. The latter compoimd is included in the analysis to provide perspective on the thermal stabihty of the inorganic system relative to the organometalhc ones. All chemical equihbrium calculations were performed with the EQUIL-code from the CHEMKIN-suite [ 100], using the thermochemical data discussed in the previous sections. The temperature range selected was 298-1023 K, the concentration of tin precursor was kept at 2 mol %, while the concentrations of oxygen and water were held at 20 mol % and 5 mol %, respectively. The total pressure was 1 atm. These conditions are similar to those used in commercial tin oxide CVD processes. Note that in the following discussion of reaction mechanisms, all heats of reaction (AHg) are given at 298 K. 

Reverse osmosis membrane separations are governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material, which is almost always a polymer, as well as its physical stmcture. Properties for the ideal RO membrane include low cost, resistance to chemical and microbial attack, mechanical and stmctural stabiHty over long operating periods and wide temperature ranges, and the desired separation characteristics for each particular system. However, few membranes satisfy all these criteria and so compromises must be made to select the best RO membrane available for each appHcation. Excellent discussions of RO membrane materials, preparation methods, and stmctures are available (8,13,16-21). 

Significant progress has been made in the application of ionic liquids (ILs) as alternative solvents to C02 capture because of their unique properties such as very low vapour pressure, a broad range of liquid temperatures, excellent thermal and chemical stabilities and selective dissolution of certain organic and inorganic materials. ILs are liquid organic salts at ambient conditions with a cationic part and an anionic part. 

Fig. 3.4. Biichi Melting Point Apparatus. Biichi Melting Point Models B-540 and B-545 can determine melting points on routine and non-routine substances in research and quality control labs of pharmaceutical and chemical companies. Both models have a temperature range from ambient to 400°C and a selection of nine heating speeds. Heating (from 50 to 350°C) takes approximately 7 min and cooling (from 350 to 50°C) takes approximately 10 min. The units can simultaneously determine melting points of three samples or two...

Parallel reactions play an important role in chemical reaction systems that involve selectivity. An example is the selective noncatalytic reduction of NO (SNCR), which is a widespread secondary measure for NO control. In this process NO is reduced to N2 by injection of a reducing agent such as NH3 into the flue gas in a narrow temperature range around 1000°C. The process is characterized by a selectivity in the reaction pathways as shown by the parallel (global) steps... 

The description of the physical properties of fluoroelastomers is necessarily less precise than that of fluoroplastics because of the major effect of adding curatives and fillers to achieve useful cross-linked materials of a given hardness and specific mechanical properties Generally, two parameters are varied increasing cross-link density increases modulus and decreases elongation, and raising filler levels increases hardness and decreases solvent swell because of the decreased volume fraction of the elastomer In addition to these two major vanables, the major determinants of vulcanizate behavior are the chemical and thermal stabilities of its cross-links The selection of elastomer, of course, places limits on the overall resistance to fluids and chemicals and on its service temperature range... 

In addition to meeting industrial and economic criteria, the precursors must be highly volatile. They are designed (new compounds) or selected (previously reported compounds) following chemically inspired guidelines. A metal-to-heteroatom bonded fragment (M-C or M-N) should be at the core of the molecule. Various substituents can be attached to the M-N or M-C core and are chosen on the basis of the decomposition mechanism that may occur at temperatures ranging from 370 to 870 K. For example,... 

Selection patents in the chemical arts can take many forms. Selections may be made from a prior art broader range of compounds or compound uses (as in the current example) but are not so limited. For example, selection inventions might also be made from prior art chemical processes where, for example, a broad temperature range or reaction time is disclosed and a later, narrower embodiment is discovered that provides a patentably distinct process. Selection inventions are also sometimes referred to as improvement inventions because the later selection may provide some unexpected result or benefit that helps overcome challenges to patentability based on assertions of obviousness of the later discovery. Obviousness challenges and rebuttals to obviousness challenges are discussed in more detail in Chapter 8. 

At first sight, adsorption and reaction are well-matched functionalities for integrated chemical processes. Their compatibility extends over a wide temperature range, and their respective kinetics are usually rapid enough so as not to constrain either process, whereas the permeation rate in membrane reactors commonly lags behind that of the catalytic reaction [9]. The phase slippage observed in extractive processes [10], for example, is absent and the choice of the adsorbent offers a powerful degree of freedom in the selective manipulation of concentration profiles that lies at the heart of all multifunctional reactor operation [11]. Furthermore, in contrast to reactive distillation, the effective independence of concentration and temperature profiles... 

Fig. 1.18. Zinc diffusion in ZnO [130]. Top Dependence of diffusivity on chemical potential and Fermi level at a temperature of 1 300 K illustrating the competition between vacancy and interstitial mechanisms. The shaded grey areas indicate the ranges selected for comparison with experimental data. Bottom Comparison between calculation and experiment. Experimental data from Lindner [137], Secco and Moore [138,139], Moore and Williams [131], Wuensch and Tuller [143], Tomlins et al. [62], and Nogueira et al. [144,145]. Solid and dashed lines correspond to regions I (vacancy mechanism) and II (interstitial(cy) mechanism) in the top graph, respectively. Reprinted with permission from [130]. Copyright (2006), American Institute of Physics...

The first issue in the preparation of the hydride slurry was the selection of the carrier fluid for the slurry. Light mineral oil has been selected for the carrier fluid because it is not chemically reactive with the metal hydride, it produces a relatively low vapor pressure, it is nontoxic, and it remains a liquid through the temperature range of-40 to 200 °C. 

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