Ates Akyurtlu

A study on the performance of the catalytic porous-wall three-phase reactor

A theoretical investigation of a catalytic porous-wall reactor in which gaseous and liquid reactants approach each other from opposite sides of the catalyst is undertaken. Equations for the annular liquid-channel are coupled with those for the catalytic wall and solved numerically and analytically using a simplified model. For the model reaction under study, the main design and operation parameters which affect reactor performance are the Thiele modulus, Peclet number, width of the liquid channel and the inlet concentration of the reactant in the liquid phase. The effect of reactor configuration is peculiar to the cylindrical geometry because the thickness and relative location of the catalytic wall as well as the selection of the liquid and gas channels can influence the reactor performance. Thin-walled catalyst tubes have larger effectiveness factors and as the tube radius approaches that of the reactor, conversion in the reactor increases especially when the liquid is saturated with the gaseous reactan...

Application of the general purpose collocation software, PDECOL, to the Graetz problem

Abstract The software package PDECOL is capable of solving coupled systems of parabolic, nonlinear, partial differential equations. Its use of B-spline collocation for spatial discretization makes it valuable for obtaining solutions in which extreme gradients are present. A severe limitation of this package is the requirement that the boundary and initial conditions be consistent. The package can, however, be modified to overcome this limitation. To demonstrate the utility of the modified PDECOL package, the solution of the classical Graetz problem is obtained for different flow geometries and for some common boundary conditions. The results indicate that excellent agreement with the analytical results can be obtained provided that a suitable distribution of a sufficient number of spatial grid points is used and an error criterion compatible with the desired accuracy is chosen for the time integration. For this steady-state problem this integration is with respect to the spatial dimension which appears in the first derivative.

DEVELOPMENT OF IMPROVED CATALYSTS FOR THE SELECTIVE CATALYTIC REDUCTION OF NITROGEN OXIDES WITH HYDROCARBONS

Significant work has been done by the investigators on the cerium oxide-copper oxide based sorbent/catalysts for the combined removal of sulfur and nitrogen oxides from the flue gases of stationary sources. A relatively wide temperature window was established for the use of alumina-supported cerium oxide-copper oxide mixtures as regenerable sorbents for SO{sub 2} removal. Preliminary evaluation of these sorbents as catalysts for the selective reduction of NO{sub x} gave promising results with ammonia, but indicated low selectivity when methane was used as the reductant. Since the replacement of ammonia by another reductant is commercially very attractive, in this project, four research components will be undertaken. The investigation of the reaction mechanism, the first component, will help in the selection of promoters to improve the catalytic activity and selectivity of the sorbents in the SCR with methane. This will result in new catalyst formulations (second component). If this research is successful, the combined SO{sub 2}-NO{sub x} removal process based on alumina-supported copper oxide-ceria sorbent/catalysts will become very attractive for commercial applications. The objective of the third component of the project is to develop an alternative SCR process using another inexpensive fuel, residual fuel oil, instead of natural gas. This innovative proposal is based on very scant evidence concerning the good performance of coked catalysts in the selective reduction of NO and if proven to work the process will certainly be commercially viable. The fourth component of the project involves our industrial partner TDA Research, and the objective is to evaluate long-term stability and durability of the prepared sorbent/catalysts. In the first year of the project, the catalysts were investigated by the temperature-programmed reduction (TPR) technique. The results from TPR indicated that the interaction with support appears to promote reduction at lower temperatures. Copper oxide in excess of monolayer coverage reduces at temperatures close to the reduction temperature of the unsupported copper oxide. Increased dispersion increases the support effect. Low activity of ceria in NO reduction may be due to its resistance to reduction at low temperatures.

Investigation of mixed metal sorbent/catalysts for the simultaneous removal of sulfur and nitrogen oxides. Semiannual report, Apr 1, 1998--Oct 31, 1998

Simultaneous removal of SO{sub 2} and NO{sub x} using a regenerable solid sorbent will constitute an important improvement over the use of separate processes for the removal of these two pollutants from stack gases and possibly eliminate several shortcomings of the individual SO{sub 2} and NO{sub x} removal operations. The work done at PETC and the DOE-funded investigation of the investigators on the sulfation and regeneration of alumina-supported cerium oxide sorbents have shown that they can perform well at relatively high temperatures (823--900 K) as regenerable desulfurization sorbents. Survey of the recent literature shows that addition of copper oxide to ceria lowers the sulfation temperature of ceria down to 773 K, sulfated ceria-based sorbents can function as selective SCR catalysts even at elevated temperatures, SO{sub 2} can be directly reduced to sulfur by CO on CuO-ceria catalysts, and ceria-based catalysts may have a potential for selective catalytic reduction of NO{sub x} by methane. These observations indicate a possibility of developing a ceria-based sorbent/catalyst which can remove both SO{sub 2} and NO{sub x} from flue gases within a relatively wide temperature window, produce significant amounts of elemental sulfur during regeneration, and use methane for the selective catalytic reduction of NO{sub x}. The objective of this research is to conduct kinetic and parametric studies of the selective catalytic reduction of NO{sub x} with NH{sub 3} and CH{sub 4} over alumina-supported cerium oxide and copper oxide-cerium oxide sorbent/catalysts; investigate SO{sub 2} removal at lower temperatures by supported copper oxide-cerium oxide sorbents; and investigate the possibility of elemental sulfur production during regeneration with CO or with CH{sub 4} air mixtures. The sorbents consisting of cerium oxide and copper oxide impregnated on alumina have been prepared and characterized. Their sulfation performance has been investigated in a TGA setup, studying mainly the effects of temperature and sorbent composition. The results of the sulfation experiments have been evaluated and presented in this report. A study to model the sulfation selectivity of the two constituents of the sorbents is also underway.

Investigation of Combined S02/N0x Removal by Ceria Sorbents

Simultaneous removal of S02 and NOx using a regenerable solid sorbent will constitute an important improvement over the use of separate processes for the removal of these two pollutants from stack gases and possibly eliminate several shortcomings of the individual S02 and NOx removal operations. Recent studies at PHC considered cerium oxide as an alternate adsorbent to CuO. The present study aims to determine the effects of ammonia on the sulfation of the sorbent and to obtain a rate expression for the regeneration of alumina-supported CeOz sorbents. In the past quarter the effect of fly-ash, ammonia, and water on the sulfation of the sorbent was investigated. The analysis of the economics of a commercial scale ceria process has been sub-contracted to TECOGEN. This work has been completed and the report has been received.

PERFORMANCE OF AN ANNULAR CATALYTIC THREE-PHASE REACTOR FOR A SECOND ORDER REACTION

A novel annular catalytic three-phase reactor is theoretically investigated for a second order hydrogenation reaction. The results indicate that the ratio of the gaseous reactant to the liquid reactant within the reaction zone of the annular reactor can be adjusted by changing the reactor dimensions and the concentration of the gaseous reactant in the feed. As a consequence, the annular reactor may have a significant advantage over the trickle-bed reactor with respect to the selectivities that may be achieved in the reactor.