Coke formation during

This experimental work gives data that help us to understand the mechanisms of coke formation during in-situ combustion. 

On the one hand, high-throughput techniques can be used to achieve more specific catalysts, while the use of conditions favoring a reduction in coke formation during the reaction (i.e., the use supercritical conditions) could also be of crucial importance in the rapid incorporation of these catalysts into industrial processes. 

Full catalyst formulations consist of zeolite, metal and a binder, which provides a matrix to contain the metal and zeolite, as well as allowing the composite to be shaped and have strength for handling. The catalyst particle shape, size and porosity can impact the diffusion properties. These can be important in facile reactions such as xylene isomerization, where diffusion of reactants and products may become rate-limiting. The binder properties and chemistry are also key features, as the binder may supply sites for metal clusters and affect coke formation during the process. The binders often used for these catalysts include alumina, silica and mixtures of other refractory oxides. 

Coke formation during xylene isomerization has been studied using in situ infrared spectroscopy [78]. A study done on EB isomerization with a bifunctional catalyst containing EUO zeolite indicated that poor initial selectivity of the catalyst improves after a period of fast deactivation, during which micropores are blocked [79]. 

Phase separation the formation of a separate phase that is usually the prelude to coke formation during a thermal process the formation of a separate phase as a result of the instability/incompatibility of petroleum and petroleum products. 

Coke formation during catalytic dehydrogenation F.M. Mandani and R. Hughes... 

Coke formation during the catalytic dehydrogenation of butene-1 has been studied in the temperature range 525-600 °C at butene-1 partial pressures of 0.05 to 0.25 bars. Moderate levels of coke deposits led to blocking of the catalyst mesopores and a hyperbolic deactivation function was found to provide the best fit to the data. Increase of temperature caused the deactivation to change from a parallel to a series coking process. 

Coke Formation during the Hydrotreating of Biomass Pyrolysis Oils Influence of Guaiacol Type Compounds... 

One can see that the derived condition of no coke formation during the main stepwise transformation (4.99) differs considerably from the necessary simultaneous satisfaction of a more rigid system of two inequalities (4.101). 

Conversion and coke formation during catalytic ethene oligomerization catalyzed by HZSM-5 have been investigated in the TEOM and in a conventional gravimetric microbalance under similar conditions (2). The results show that the TEOM is a powerful tool for determination of the kinetics of deactivation of catalysts, with a design that makes determination of the true space velocity (or space time) easy. The TEOM combines the advantages of the conventional microbalance with those of a fixed-bed reactor, and the same criteria can be used to check for plug flow and differential operation. 

Hershkowitz et al. (3,10,11) measured adsorption and coke deposition on zeolite catalysts as well as catalytic cracking activity of FCC catalysts in short-contact-time interactions with decane at 573 K. They used 5 pi liquid decane injections to the catalyst bed to simulate FCC reaction conditions. Hershkowitz et al. focused on the measurement of adsorption and coke formation during the flow of the pulses. 

Y. H Lin, P. N. Sharratf A. A. Garforth, and J. Dwyer, Deactivation of US-Y zeolite by coke formation during the catalytic pyrolysis of high density polyethylene, Thermochimica Acta, 294, 45 (1997). 

Burke, N. and David, T. Coke formation during high pressure catalytic partial oxidation of methane to syngas. Reaction Kinetics and Catalysis Letters, 2005, 84, 137. 

Figure 3 Coke formation during n-heptane cracking at 350°C over dealuminated HY zeolites.

The effect of coke formation during the MTO reaction over SAPO-34 at 425°C can be summarized as follows ... 

The obstruction of micropores or the blocking of the active sites of a catalyst by coke formation during a chemical transformation is one of the major problems encountered in zeolite deactivation. Moreover, catalysts are usualfy used in extruded form and the problem then is to know which part of this extrudate is active. 

Figure 3 Surface area changes and coke formation during the initial stages of catalyst deactivation.

Finally, it is relevant to observe that this dissolution presents strong analogies with a condensation process discussed and stressed by several authors (Cai et al., 2002) as being responsible for coke formation/deposition in the TLE tube outlet section at operating temperatures of 350 450°C. Indeed this mechanism can be explained on the basis of the solubility of heavy species of the process fluid phase in the soft polymer. There has also been research into the computer generation of a network of elementary steps for coke formation during steam cracking process (Wauters and Marin, 2002). 

Spectroscopic methods have also been usefully applied to the problem of coke formation during MTG, addressing questions such as what is the chemical constitution of the coke, where is it formed, how is it formed and how can it be 13... 

In contrast to catalytic treatment, coke formation during thermal treatment leads only to pipe blocking and poor thermal conductivity of the reactor walls. The most important difference between coke formation in catalytic and thermal treatment is that a free radical mechanism in coke formation is not possible in the case of thermal processing. 

The rate or velocity of coke formation is, first of all, a function of the feedstock characteristics. Seidel [1] reported about the tendencies of different components of heavy vacuum residues to coke formation. The following sequence shows a descending tendency to coke formation during thermal treatment ... 

In the same way, a model of asphaltenes as a product of the thermal treatment of VR/plastics blends was investigated (Fig. 9.5a-c). The destruction of aromatic cores of asphaltenes can be clearly observed during the co-processing of VR and plastics. This can explain the minimization of coke formation during the cocracking of VR and plastics. 

The investigation into the influence of paraffinic plastics on asphaltene chemistry during thermal cracking showed that pure plastics affect only the equilibrium of alkylation reactions by the increase of the paraffinic radicals in the reaction zone (Figure 9.18). This means that asphaltene decomposition will be slowed down. As such, there will be no decomposition to form aromatic cores without paraffinic periphery. This decelerates polycondensation and coke formation during the thermal treatment of mixtures of vacuum residue and plastics. However, it does not promote the cracking of the asphaltenes. 

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