Kinetics Of Coke Combustion Research Articles

Effect of particle size on the kinetics of pure oxygen combustion of coke

Non-isothermal thermogravimetry technique was used to analyze three groups of coke samples (S-ZD, M-ZD, and L-ZD) of varying particle sizes. The effect of particle size on kinetic parameters was studied in a pure oxygen atmosphere. The ignition (Ti), peak (Tp), and burnout (Tf) temperatures and the flammability (C) and combustion characteristic (Sn) indexes were determined by varying the heating rate (β). The activation energy (Eα) was evaluated following the Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods. Ti, Tp, Tf, C, and Sn correlated positively with the increase in β in a pure oxygen atmosphere. The order of ignition was L-ZD > M-ZD > S-ZD, and the Eα values for the S-ZD, M-ZD, and L-ZD samples were 98.49, 98.35, and 95.17 kJ·mol−1 (FWO) and 90.32, 90.92, and 89.25 kJ·mol−1 (KAS), respectively. Particle size exerted little effect on the kinetics of coke combustion.

Coke combustion kinetics of spent Pt-Sn/Al2O3 catalysts in propane dehydrogenation

The kinetics of coke combustion was investigated by using a thermogravimetric analyzer (TGA) of coked catalysts which was used for propane dehydrogenation to determine the activation energy. Apart from the Pt/Al2O3 catalyst, four different Pt-Sn/Al2O3 catalysts were prepared by varying the Pt/Sn ratio from 3: 0.5 to 3: 3 by weight. The catalytic activity was measured by propane dehydrogenation at 620 °C. The reactant mixture consisting of C3H8 (30 ml/min) and H2 (30 ml/min) was fed into the reactor for 5 h. A thermogravimetric analyzer in the presence of air was used to determine the amount of coke deposited and calculate the kinetic parameters for coke combustion. Three non-isothermal models (Friedman, Flynn-Wall-Ozawa (FWO), and Kissinger-Akahira-Sunose) were used to determine the activation energy and the best model to fit the experimental data. The FWO model provided the best fit for 3Pt/Al2O3 and 3Pt-0.5Sn/Al2O3. The three models were equivalent for fitting the data for 3Pt-1Sn/Al2O3, 3Pt-2Sn/Al2O3, and 3Pt-3Sn/Al2O3. The activation energy increased with increasing Sn addition in the 3Pt/Al2O3 catalyst. Differences in the locations and the qualitative features of the cokes were suggested to interpret the results.

Combustion kinetics of the coke on deactivated dehydrogenation catalysts

The coke combustion kinetics on the deactivated catalysts for long chain paraffin dehydrogenation was studied by the thermogravimetry and differential thermogravimetry (TG–DTG) technique. The amount and H/C mole ratio of the coke were determined by the TG and elemental analysis. And the comprehensive coke combustion model and catalytic combustion mechanism were also proposed. The results showed that three types of coke existed, which were located on the metal sites (C1) and the support sites surrounding (C2) and far from Pt (C3), respectively. The reaction order with respect to carbon was 1, 1/3 and 3/4, and to oxygen was 0, 1/2 and 3/4, respectively for the coke C1, C2 and C3. Moreover, the corresponding activation energy was 31, 107 and 127kJ/mol, respectively.

Deactivation and coke combustion studies of nanocrystalline zeolite beta in catalytic cracking of used palm oil

Nanocrystalline zeolite beta was synthesized and its catalytic cracking activity for the production of biofuel from used palm oil was determined. The catalyst was characterized for its crystallinity, surface properties and morphology. The effect of reaction temperature on the catalytic cracking activity of nanocrystalline zeolite beta was also studied. The catalyst deactivation was monitored with the time on stream data by varying the palm oil to catalyst ratio of 6–14 at different temperatures. The deactivation data were analyzed using activity models and the deactivation parameters were obtained. The combustion behavior of the coked nanocrystalline zeolite beta derived at various coking temperature was studied by thermogravimetric analysis (TGA). The regeneration of the cracking catalyst was strongly correlated with the coke combustion kinetics. The coke combustion kinetics was studied and activation energy for coke combustion was determined.

Coke Aging and Its Incidence on Catalyst Regeneration

The effects of a sweeping treatment on the activity recovery, coke content, H/C ratio, and kinetics of coke combustion have been studied in the coke deposited on an HZSM-5 zeolite. The reaction tes...

Regeneration of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins

The regeneration by coke combustion of a catalyst based on a SAPO-34 used in the transformation of methanol into olefins (ethene and propene) has been studied. It has been observed that coke combustion kinetics are strongly dependent on the nature of the coke (H/C ratio), which in turn is a consequence of the reaction conditions (especially of the water content in the feed) and of the ageing level of the coke prior to its combustion. A severe ageing treatment is needed in order for combustion kinetics to be reproducible. Combustion is delayed due to the fact that coke is not an inert material but is bound to the acid sites. © 1999 Society of Chemical Industry

Chemical characteristics and kinetics in regeneration of Pt-Sn/Al2O3 reforming catalyst

The kinetics of coke combustion, platinum sintering in a non-hydrogen atmosphere, and redispersion on Pt-Sn reforming catalyst were investigated. By using the kinetic results, mathematical simulation of coke burning in a radial continuous regenerator was established. Good agreement was obtained between simulation-calculated and measured temperatures. The oxygen in the gas may enhance resistance to sintering at high temperatures in the presence of water. The sintered platinum on the catalyst, if there had been no decrease of the support surface area, can be completely redispersed through chlorination and oxidation.

Multiplicity of the steady state in fluidized bed reactors—IV. Fluid catalytic cracking (FCC)

A mathematical model for fluid catalytic cracking units is developed. The model takes into account the kinetics of the cracking reactions, as well as the kinetics of coke combustion in the regenerator. A numerical scheme is developed for the solution of the model equations. It is found that multiplicity of the steady states extends over a wide scope of operating variables and parameters. The model investigates the effects of catalyst circulation rate and gas oil flow rate, which have a strong effect on the reactor temperature and hence yield and selectivity. The phenomenon of hysteresis has been investigated. The model can be used for yield optimization and steady state control.