Coke bands

Ageing causes a large change in the IR coke bands. The effect of ageing on the absorbance of the four main bands in the 1655-1350 cm region is shown in figure 2 for values of reaction times between 2 and 60 minutes and of ageing times of 1 and 6 hours. 

The intensity of the band at 1600 cm (the so-called coke band) which is considered as characteristic of polyaromatic species [3] increases slightly with ageing as well as those of the bands at 1450 cm and at 1355 cm whereas the intensity of the band at 1505 cm which corresponds to less condensed aromatics [8] decreases. Therefore, in addition to the decrease in coke content there is an increase in the degree of aromaticity of coke. Similar observations have been previously made by various authors on zeolites [9-13] as well as on other acid catalysts [14-16]. However, the sweeping under inert gas flow of the coked samples was always carried out at temperatures much higher than in this work. 

The FTIR spectra of the soluble coke showed bands at 3010, 1480 and 780 cm assigned to C-H and C-C stretching and C-H and C-C deformation respectively, which are typical of aromatics. The spectra also showed typical absorption bands for aliphatic hydrocarbons at 2960 and 2800 cm for CH3 and at 2930 cm for CH2 groups [18], The coke band due to the presence of polyolefins and/or polycondensed aromatics [19, 20] was present as a shoulder at 1585 cm No significant difference was noted among the spectra. Figure 2 illustrates the curves obtained. The presence of aromatics was confirmed by UV spectra by the presence of a band in =262 nm [21],... 

Freshly activated sample (2)-(7) coked samples, tcoking tinie on stream during coking Do [EB] Fickian diffusivity of ethylbenzene n sorption capacity for ethylbenzene at = 395 K under Ap [EB] = 0 115 Pa An/n percentage of loss of sorption capacity A [1490], A [1610] maximum absorbance of typical coke bands at 1490 and 1610 cm respectively, as a measure of coke deposited. The error of the diffusivity values is about... 

FTIR spectroscopy is particularly suitable for studying the deactivation of acid zeolites by coking [11,13-24]. Indeed it can give simultaneously information i) about the amount of coke (by the intensity of the so-called coke band around 1585 cm" ) and the chemical identity of its components and ii) about the properties of the catalyst surface e.g. the concentration of OH groups as a function of the coke content. 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

The necessity of forcing activation conditions has been attributed to the production of various carbonaceous species during activation. Under oxidizing atmospheres, the appearance of stretching frequencies consistent with the formation of surface carboxy-lates has been reported. Similarly, several persistent surface bands consistent with coke-type species were identified when activating supported Ru DENs under H2. °... 

Recently, UV laser stimulation of catalyst samples has been developed to overcome the problem of interference by coke (carbon deposition) on catalysts.Fig. 9 shows a typical Raman data set that was obtained for carbon deposition as a function of temperature. To explore different coke formation behavior, the reaction of propene on a zeolite was performed. The spectra obtained were (A) C3H6/He flow at 773 K for 3 h (B) O2 flow at 773 K for 1 h and (C) O2 flow at 873 K for 1 h. This data shows that most of the carbon, identified as polyaromatic and pregraphite, can be removed at 773 K with oxygen. However there is still carbon present as identified by the broad band at 1610 cm suggesting that carbon is in a more inert form such as coke. Not until the temperate is taken to 873 K with oxygen is that carbon removed. 

Transitional material between anthracite and coke. The variations in the appearance of the banding are caused by variations in composition and anisotropy. No vacuoles developed. Banding was retained in this unity which occurs 652 feet below the siU... 

A—Pyrolytic carbon showing ribbon-like structure in vitrinoid bands. B—Faint gray lines define compression cracks in a bright micrinoid particle. C—Pyrrhotite (white) formed by the thermal decomposition of pyrite impregnating semifusinoids (gray). D—Bright coke particles in a baked-bone coal layer... 

Under the optical microscope the texture of products derived from the three coals studied show an anisotropy of the type which already has been described for similar materials (I, 4, 9). The texture of the l.t. pitch coke is entirely isotropic, whereas the h.t. pitch coke is characterized by a pronounced anisotropy in bands. The anisotropy of the carbonization products of mixtures of l.t. and h.t. pitches varies linearly as a function of the composition of the mixture (8). 

Figure 7. Natural coke and basaltic sill at Sopris locality. Silver dollart for scale, rests against band of well- fingered natural coke. A band of the sill is lighter material beneath...

Figure 2 shows a multiple-echo, intensity-weighted cyclohexane MRM image of a 300 pm cross-sectional slice of a 4 mm diameter coke bean. The density-weighted H images are collected with an unprocessed image resolution of 24 pm pixel"1. Since the coke is packed in wet gypsum, the area outside the coke shows very little cyclohexane intensity and appears black. Several feature arise from this image which complement the SEM images in Figure 1. Firstly, a dark band at the perimeter of the coke corresponds to the exterior shell depicted in deal in Figure lc. This dark feature reflects the absence of cyclohexane and thus indicates the...

Bituminous coal is a dense coal, usually black, sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke. The moisture content of bituminous coal is usually less than 20% by weight. The heat content of bituminous coal ranges from 21 to 30 million Btu/ton on a moist, mineral-matter-free basis. 

A large buildup of iron and titanium was found in a narrow band of the catalyst exterior of a spent catalyst. Improved catalyst aging is likely to occur by the use of an ebullated bed reactor, primarily by decreased interparticle coke formation as well as by mild abrasion of metal contaminants. 

Band-Aging - Especially with fresh catalysts, the reaction occurs over a relatively small zone in a fixed bed. This reaction front marches down the catalyst bed as the coke deposits first deactivate the front part of the bed (Figure 4). Use of a sufficient catalyst volume permits a fixed-bed design in which on-stream periods are long enough to avoid overly frequent regeneration cycles. 

Particle Temperature Overshoot. The temperature of the burning char particles will run hotter than that of the bed by amounts that depend upon particle size, reactivity, bed temperature. It is determined in part by the heat released at the particle surface due to reaction and in part to the additional heat released by carbon monoxide oxidation near the particle surface (54-58). Measurements for 1.8 to 3.2 millimeter size coke particles burning in a fluidized band of sand at 1173 K increased from the bed temperature at low oxygen concentrations to values 150 to 200 K above the bed temperature for oxygen concentrations approaching that of air (72). Estimation of this temperature rise is important for purposes of evaluating the NO/C reaction and also for prediction of the burnout times of fines. 

Sample Coke (IR) H/C (mol/mol, element analysis) Width 1600 cm-1 Raman band (cm-1) ... 

According to Figure 3, Lap showed the simplest spectrum with five bands at 250, 305, 320, 370 and 470 nm. Spectra of LaY and ASA contained bands at 240, 260, 300, 400, 420, 470 and 560 nm. In the spectrum of spent SZR catalyst no separated bands could be distinguished, with the overall absorption being characteristic for really coked catalyst. 

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