Coking propensity

Density Pour point Coking propensity Shear stability Elastomer compatibility... 

SAE ARP 5996A. Evaluation of Coking Propensity of Aviation Lubricants Using the Hot Liquid Process Simulator (HLPS) Single Phase Flow Technique. SAE International. 

In addition to size exclusion and steric inhibition, the intermolecular forces between the zeolite and sorbate molecules offer opportunities to achieve unique selectivity based on competitive sorption properties of various zeolites. Variables such as silica to alumina ratio, the nature of the cation species and the geometry of the channels have been shown to be important factors for consideration (13-14). They also can contribute to catalyst stability and reduced coking propensity, two important characteristics of commercially useful catalysts. 

Asphaltene concentrations can be as high as 18% in certain Athabasca bitumens. Athabasca bitumen is one of the largest reserves of bitumen in the world [4]. The aggregation and coking propensity of asphaltenes causes fouling in bitumen upgrading processes [3,4]. 

Walters KM, Dean AM, Zhu H, Kee RJ (2003) Homogeneous kinetics and equilibriiun predictions of coking propensity in the anode channels of direct oxidation solid-oxide fuel cells using dry natural gas. J Power Sources 123 182-189... 

A further important aspect of carbon inertness in catalysis is its much lower coking propensity in comparison with alumina or silica supports. Coke deposition on the surface of the catalyst reduces the life of the catalyst. De Beer et al. (1984) studied this effect and found that the extent of carbon deposition on the blank supports is higher for carbons than for alumina and it increases with increasing surface area. In the absence of a metallic component the cracking appears to be related more to the accessible surface area than to any other particular surface property. However, the addition of metals to the supports causes an increase in the rates and amounts of carbon deposition, but the increase is much higher for the alumina-supported catalysts. 

Rahimi, P. Gentzis, T. Kubo, J. Fairbridge, C. Khulbe, C. Coking propensity of Athabasca bitumen vacuum bottoms in the presence of H-donors - formation and dissolution of mesophase from a hydrotreated petroleum stream (H-donor), Fuel Proc. TechnoL, 1999, 60, 157. 

Fig. 3 shows that H-mordenite, while exhibiting an excellent selectivity, undergoes rapid deactivation which, without any doubt, is due to coking. The propensity of H-mordenite towards deactivation is well known from many other reactions and has generally been... 

Data reporting (i.e., the statement of the results of the proximate analysis test methods) usually includes (in some countries but not in all countries) descriptions of the color of the ash and of the coke button. As an interesting comparison, the test for determining the carbon residue (Conradson), the coke-forming propensity of petroleum fractions and petroleum products (ASTM D-189 ASTM D-2416), advocates the use of more than one crucible. A porcelain crucible is used to contain the sample, and this is contained within two outer iron crucibles. This corresponds to the thermal decomposition of the sample in a limited supply of air (oxygen) and the measurement of the carbonaceous residue left at the termination of the test. 

The carbon residue (ASTM D-189 and ASTM D-524) of a crude oil is a property that can be correlated with several other properties (Figure 2-14). The carbon residue presents indications of the volatility or gasoline-forming propensity of the feedstock and, for the most part in this text, the coke-forming propensity of a feedstock. Tests for carbon residue are sometimes used to evaluate the carbonaceous depositing characteristics of fuels used in certain types of oil-burning equipment and internal combustion engines. 

Carbon residue the amount of carbonaceous residue remaining after thermal decomposition of petroleum, a petroleum fraction, or a petroleum product in a limited amount of air also called the coke- or carbon-forming propensity, often prefixed by the terms Conradson or Ramsbottom in reference to the inventor of the respective tests. 

We report die effect on the kinetics of coking and on the activity of the deactivated catalyst when a species with a different propensity to coke formation is added to the feed. Steamed REHY zeolite was used as the catalyst, and feeds containing various... 

Enhancement of reaction conversion by employing a permselective membrane often has the implication that, for a given conversion, it is possible to run the reaction at a lower temperature in the membrane reactor than in a conventional reactor. Catalyst deactivation due to coke formation generally becomes more severe as the reaction temperature increases. Therefore, the use of a membrane reactor to replace a conventional one should, in principle, reduce the propensity for coke formation because for the same conversion the membrane reactor configuration may be operated at a lower temperature than a conventional reactor. This is particularly true for such reactions as dehydrogenation. 

Since coke causes a decrease in catalytic activity for all reactions, it is obvious that it deactivates some catalytically active sites on the catalyst. If all the active sites have equal propensity for coverage of coke and are consequently completely deactivated towards reaction, then the activation energy should remain the same for the remaining unaffected sites, since activation energy does not depend on the number of sites present. This assumes that a deactivated site has no activity and that the activation energy of an uncovered site is not affected... 

The most significant rate parameters are those calculated for Pi, P2 and P4. For all coked substrates, the corresponding A-factors and activation energies for these peaks are a similar magnitude. Any differences in A-factors between equivalent peaks for different substrates can be associated with differences in the amount of carbon per peak. Hence reflecting the propensity for coke formation. Similar activation energies for corresponding P2 and P4 indicate the oxidation reactivity of the final "hard coke is independent of the initial hydrocarbon source of the coke. 

The effect of quinoline and phenanthrene additions to a n-hexadecane feedstock has been determined for a model four-component FCC catalyst by means of a MAT reactor with analysis of all products and characterisation of the coke produced. Both additions lead to an overall loss in conversion quinoline is considered to act as a poison while phenanthrene participates strongly in coke formation and the resultant coke becomes more aromatic in nature. The cracking propensity and associated coke formation have been measured for a series of FCC catalysts with differing compositions. Increasing amounts of zeolite in a matrix lead to increasing extents of conversion but with little effect on the extent of coke production. However, a pure zeolite gave a very high coke content. 

CO2 reforming of methane can be used to adjust the H/CO ratio and provide the correct H2/CO ratio for Fischer-Tropsch synthesis and could potentially be used to reduce CO2 emissions from other processes however, it is even more endothermic than steam reforming. Partial oxidation is exothermic and has the correct H2/CO ratio for methanol synthesis, but requires a pure oxygen source, adding to the cost. In addition to the individual drawbacks, all of these processes must be run with 0/C ratios of greater than 1 to prevent coking of the catalyst. This makes the processes more expensive in practice than would be expected under optimized conditions for the stoichiometric reactions. The propensity of these processes to form carbon at low 0/C ratios is even more pronounced at... 

Therefore, the minimization of coking is one of the major factors controlling the industrial application of SR. The thermodynamic of the process dictates reaction conditions that favour coke formation cannot be avoided, but operating conditions can be chosen to minimize coke. Temperature, pressure and feed composition must be carefully controlled to avoid catalysts deactivation due to coking. Perhaps, the most obvious way is to increase the steam to hydrocarbon ratio to favour the reverse of reaction (2.8). Rostrup-Nielsen et al. [13] have presented carbon hmit diagrams which relate the propensity of the catalyst to coke formation as function of to the H/C and O/C ratios in the gas phase. 

The carbon residues of petroleum and petroleum products serve as an indication of the propensity of the sample to form carbonaceous deposits (thermal coke) under the influence of heat. 

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