Coke Reduction Research Articles

Thermodynamic study of phosphogypsum decomposition by sulfur

Phosphogypsum (PG) is one of the most significant industrial solid wastes from the phosphorus chemical industry. In order to utilize PG more effectively, a new decomposition process of PG by sulfur as a reducer is proposed in this work. Thermodynamic study of the sulfur reduction process including two-step reactions was carried out by both thermodynamic simulation and experimental research. The simulation results indicate that sulfur changes its form in a complex way with rising temperature. The final decomposition temperature of PG by simulation is 993K in the first-step reaction, and this is in good agreement with that obtained by the experiments. For the second-step reaction, however, the final PG decomposition temperature from the experiments is 250K lower than the simulation results predict. The reaction heat of the sulfur reduction process is 27.95% less than that of the traditional coke reduction process at T=1473K based on enthalpy change calculations. This new process can reduce the emission of CO2 effectively and is more suitable for resource utilization of PG than the coke reduction process, so it may be a promising method for sulfuric acid production from PG.

Simultaneous Coke Reduction with Improved Syngas Production during Propane Steam Reforming using Forced CO2 Cycling

Carbon deposition during hydrocarbon steam reforming is often a major cause of pathological reactor performance and catalyst deactivation. In this paper, we report the effect of forced periodic cycling between propane-steam reforming feed and a carbon gasifying agent (CO2) as a novel reactor strategy to both improve product yield (H2 and CO) and catalyst longevity. Experiments were carried out over Co-Ni/Al2O3 catalyst in a fluidized bed reactor. Cycle period, ?, was varied between 5 to 20 mins at 5 different cycle splits, (0.1 ? s ? 0.9). Both H2 and CO formation rates were higher (up to 5-fold and more than 10-fold, respectively) than that attainable under steady-state operation at all periods investigated. In particular, the time-average H2:CO ratio was lower (< 3.0) than the steady-state equivalent for the pure propane steam reforming (14.0), although it increased monotonically with cycle split. Composition cycling with CO2 also improved catalyst stability and longevity compared to steady-state performance at the cycle periods examined. This strategic reactor operation is therefore a potentially useful key to green process engineering in the overall petrochemical plant design to effect greenhouse gas emission reduction.

Mathematical Modelling and Experimental Investigation of Coke Reduction of FeO in Slag

Mathematic model development and experimental investigations were carried out for the reduction of FeO in slag by coke. Rate expressions for the reduction limited by the different steps and through different reaction routes were proposed. In the experimental investigation, the FeO reduction was found to be a first order and irreversible reaction; the reduction rate increased with increasing temperature and the FeO content in slag, and decreased with increasing ash content in the coke. Low CO2/CO ratio in the product gas and preferential reduction of FeO over SiO2 in slag were observed in the reaction system. The proposed reaction mechanisms were discussed with the observed kinetic phenomena. The reduction of FeO in slag by coke was found most likely to be jointly dominated by the mass transfer of FeO in slag and the chemical reactions at slag‐coke, slag‐gas or slag‐metal interfaces.

Density functional theory studies of methane dissociation on anode catalysts in solid-oxide fuel cells: Suggestions for coke reduction

We studied the dissociation of methane into adsorbed carbon and hydrogen atoms on various surfaces to gain insight into carbon coke formation on solid-oxide fuel cell anodes. Preferred adsorption sites and energies were calculated for CH x ( x = 0 , … , 3 ) and H on Ni and Cu (111) planar and (211) stepped surfaces, on Cu Ni and Cu Co surface alloys, and on Ni(211) surfaces with step edge sites blocked by Au- and S-promoter atoms. Transition states and kinetic barriers were calculated on Cu(111) and Cu(211) and on the S Ni(211) surface. Our results are in excellent agreement with existing experimental and theoretical studies, suggesting that copper anodes have very low activity and high resistance to coking, and that step-blocking on the nickel surface can increase the tolerance of nickel-based anodes to carbon coke formation.

99/03912 Coke reduction and coil life extension. A coil vendor's viewpoint: Jones, J. J. and Huber, J. Proc. Ethylene Prod. Conf., 1998, 7, 105–125

99/03912 Coke reduction and coil life extension. A coil vendor's viewpoint: Jones, J. J. and Huber, J. Proc. Ethylene Prod. Conf., 1998, 7, 105–125

On the activity and stability of platinum/alumina catalyst during multiple deactivation and regeneration

AbstractCatalyst surface characterizations have been carried out to investigate the role of dispersion on catalyst activity and to probe the occurrence of oscillations in coking levels with cycle number generally observed during multiple deactivation and regeneration schemes. The titrations were done, cycle by cycle, at 430°C after oxidation and at the same temperature (430°C) after reduction at 500°C. Results show the usually observed trend ‐ that the dispersions after oxidation are higher than those after reduction. The average decline in dispersion from oxidation to reduction was calculated to be 39.25%. It was observed that the cycles with high toxic coke removal were characterised by high deactivation times. The deactivation times were still high even for cycles subsequent to those with low dispersion. At high dispersions the catalyst had short deactivation times, that is the small crystallites deactivate faster than large ones. The nature of reducebale coke and the efficiency of its removal is a much more determinant factor of catalyst activity than the level of metal disperision. Thus prolonged toxic coke reduction at the high temperature of 500°C, though resulting in an apparent lowering of dispersion, does not affect the quality of the catalyst. The dispersion before reduction could be retained on oxidation. Hence reduction at 500°C did not introduce sintering.