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Window temperature

Determination of the thermal decomposition temperature by thermal gravimetric analysis (tga) defines the upper limits of processing. The tga for cellulose triacetate is shown in Figure 11. Comparing the melt temperature (289°C) from the dsc in Figure 10 to the onset of decomposition in Figure 11 defines the processing temperature window at which the material can successfully be melt extmded or blended. [Pg.258]

The precious-metal platinum catalysts were primarily developed in the 1960s for operation at temperatures between about 200 and 300°C (1,38,44). However, because of sensitivity to poisons, these catalysts are unsuitable for many combustion apphcations. Variations in sulfur levels of as Httle as 0.4 ppm can shift the catalyst required temperature window completely out of a system s operating temperature range (44). Additionally, operation withHquid fuels is further compHcated by the potential for deposition of ammonium sulfate salts within the pores of the catalyst (44). These low temperature catalysts exhibit NO conversion that rises with increasing temperature, then rapidly drops off, as oxidation of ammonia to nitrogen oxides begins to dominate the reaction (see Fig. 7). [Pg.511]

From this discussion, the limitations of the force field should have become clear. There is no such thing as a universal force field which describes every system in every condition. The force field is a function with few adjustable parameters and can, therefore, not be expected to reproduce all properties of all chemical species under all circumstances. This means, for example, that an OH group in an aliphatic alcohol will have to be treated differently from a phenolic OH or from the OH of a carboxylic acid group. Similarly, the density and temperature window of a force field is often limited [22]. [Pg.487]

Batteries with a high operating temperature, of about 300 °C, require high-efficiency insulating jackets to maintain the temperature within an acceptable range. Especially in non operating periods, the battery should not cool down. It was requested that batteries should keep their operating temperature window for at lest four days. This requires heat loss rates of less than 200 W for a 40 kWh battery. [Pg.587]

Frequency factors arc often determined from data obtained within a narrow temperature window. For this reason, it has been recommended4 that when extrapolating rate constants less error might be introduced by adopting the standard values for frequency factors (above) than by using experimentally measured values. The standard values may also be used to estimate activation energies from rate constants measured at a single temperature. [Pg.24]

The temperature window for mixing of silica compounds is rather narrow, limited by the decreasing silanization rate and increasing risk of scorch. High temperatures improve the sUaniza-tion rate due to the temperature dependence of the reaction and the enhanced rate of alcohol... [Pg.804]

Careful energy cahbration on each detector was done to achieve optimal detection rate. Each SH was temperature cycled (153-293 K). During cycling energy spectra were measured. As a result of the analysis of these spectra, optimal firmware parameters were calculated for each detector and each temperature window. During operation instrument firmware automatically adjusts those parameters depending on temperature and ensures best detector performance. [Pg.67]

Various other classes of catalysts have been investigated for NH3-SCR, in particular, metal-containing clays and layered materials [43 15] supported on active carbon [46] and micro- and meso-porous materials [31b,47,48], the latter also especially investigated for HC-SCR [25,3lb,48-53], However, while for NH3-SCR, either for stationary or mobile applications, the performances under practical conditions of alternative catalysts to V-W-oxides supported on titania do not justify their commercial use if not for special cases, the identification of a suitable catalyst, or combination of catalysts, for HC-SCR is still a matter of question. In general terms, supported noble metals are preferable for their low-temperature activity, centred typically 200°C. As commented before, low-temperature activity is a critical issue. However, supported noble metals have a quite limited temperature window of operation. [Pg.4]

However, some areas of future research need to be highlighted (1) noble metal-based formulations which do not form N20, (2) novel catalyst formulations which decompose/reduce N20 below 300°C, (3) on-board routes to form oxygenated reductants, (4) NTP technologies, (5) maintain catalyst within peak operating temperature window and (6) techniques for storing NO, emissions during cool exhaust conditions followed by re-injection of the stored NO when the catalyst has achieved light-off conditions. There is already an active research on these topics, but a further intensification would be necessary. [Pg.8]

A final relevant parameter is the temperature window in which the conversion of NO is at the maximum value. In fact, due to the presence of the side combustion of ammonia, the conversion of NO typically decreases at temperatures above the maximum. The presence of a sharp or broader maximum is related to the rate of reaction of ammonia... [Pg.10]

This question has to be answered to completely understand the DeNOx process, and design the final efficient catalyst, according to the nature of reductant and the experimental conditions (more particularly, temperature window). [Pg.146]

SCR systems at stationary diesel engines profit from the high exhaust gas temperatures of about 350-400 C, caused by the usually constant high load operation conditions of the diesel engine. In this temperature window nearly all known SCR catalysts are very active. Moreover, weight and size of the exhaust gas catalyst are usually not strictly limited, which results in a good NO, reduction efficiency (DeNOJ. However, DeNO, is not the only criterion for an SCR catalyst. Further requirements are excellent selectivities regarding NO and urea/ammonia as well as low ammonia slip, which is an undesired secondary emission of the SCR process. Therefore, all SCR catalysts exhibit surface acidity, which is necessary to store ammonia on the catalyst surface and, thus, to prevent ammonia slip. [Pg.262]

Figure 5 Time-resolved IR thermographic imaging of the enantioselective hydrolysis of epoxide (48c) catalyzed by >S,//-(50a-c) after (a) 0, (b) 2.5, (c) 4, (d) 5, (e) 7, (g) 8, (h) 15, and (i) 32 min. In (f) the same images is shown as in (e), except that the temperature window ranges over 10 K. The bar on the far right of each image is the temperature/colour key of the temperature window used (°C).SS... Figure 5 Time-resolved IR thermographic imaging of the enantioselective hydrolysis of epoxide (48c) catalyzed by >S,//-(50a-c) after (a) 0, (b) 2.5, (c) 4, (d) 5, (e) 7, (g) 8, (h) 15, and (i) 32 min. In (f) the same images is shown as in (e), except that the temperature window ranges over 10 K. The bar on the far right of each image is the temperature/colour key of the temperature window used (°C).SS...
Thus, in the process of Li+ reaction with tin, theoretical capacity of Li-Sn alloys can reach up to 790 mA-h/g. Theoretical capacity of pure Sn is 994 mA-h/g (7234 mA-h/cm3). Formation of such alloys occurs in the range of potentials from 0 to 0.8V versus lithium (Table 2) or in the temperature window 0-800°C. Charge-discharge curves have an inclined form. [Pg.323]

Figure 6.5 shows the process configuration of different FB gasification concepts, from single-reactor concepts to twin fluid-bed systems. The FB gasifiers are operated in a typical temperature window of 800-950°C. Producers of such FB gasifiers (also including air... [Pg.193]

Figure 6.20 shows an example in which QEXAFS has been used in combination with XRD to study the temperature programmed reduction of copper oxide in a Cu/ZnO/Al203 catalyst for the synthesis of methanol [43,44]. Reduction to copper metal takes place in a narrow temperature window of 430-440 K, and is clearly revealed by both the EXAFS pattern and the appearance of the (111) reflection of metallic copper in the XRD spectra. Note that the QEXAFS detects the metallic copper at a slightly lower temperature than the XRD does, indicating that the first copper metal particles that form are too small to be detected by XRD, which requires a certain extent of long range order [43,44],... [Pg.180]

Modem catalysts have to be very active and very (100%) selective, that is, they have to catalyze the desired reaction in the temperature window, where the equilibrium conversion is the highest possible and the reaction rate is high enough to permit suitable process economics. To engineer the reaction, one has to obtain first the intrinsic reaction rate, free of heat- and mass-transfer limitations. In many cases this is very difficult, because in the core of the catalytic process there are several physical and chemical steps that must occur and which may preclude the reaction running in the kinetic regime. These steps are as follows ... [Pg.199]

The product HNN provides a plausible route for the overall NO reduction mechanism, which permits the determination of the temperature window. Miller and Bowman [6] proposed the competitive channels shown in Table 8.2 as the explanation. [Pg.438]


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