Optimization of the reactor–regenerator system with catalytic parallel–consecutive reactions

In catalytic processes with catalyst deactivation, there is a big problem in estimating the remaining catalyst lifetime since industrial operating conditions are quite uncertain and consequently the non-uniform catalyst activity profile developed in the reactor during operation is unknown. In this article, a simple method for calculating the remaining catalyst lifetime from present operating data is reported. The spatial average catalyst activity, which indicates how much the catalyst has been deactivated, is proposed to denote the present catalyst activity in the reactor. For an isothermal plug flow reactor packed with non-porous catalyst, any catalyst activity profile determines the same reactant conversion if the spatial average activity related to this profile is the same. As a result, the average activity is easily calculated from present operating data without the information of the catalyst deactivation rate. The determined present average activity is used as an initial condition to estimate the remaining catalyst lifetime providing superbly accurate calculation results when the kinetic deactivation expression is characterized by the first order in the catalyst activity. The developed procedure is demonstrated using the water–gas shift reaction and methane steam reforming processes as examples.

High purity, carbon monoxide-free hydrogen and filamentous carbon can be produced by thermo-catalytic cracking of methane. Carbon filaments continue to grow until the catalyst deactivates because of carbon encapsulation. Regeneration of catalyst is important to maintain a continuous process. Our work on optimization of the partial regeneration method showed that activity of the catalyst can be sustained for longer times by gasifying not all but some extent of the deposited carbon. In the previous work, a kinetic model was developed to be able to understand the reaction mechanism of deactivation of fresh catalyst at the molecular level. The objective of this study was to develop a well-fitted kinetic model for deactivation of regenerated catalyst. A kinetic model that consists of surface reactions, filament formation, and deactivation was developed for the regenerated catalyst. It is assumed that reaction parameters at the molecular level do not change when the burn off degree is at a moderate extent but these parameters changed drastically when burn off degree is vastly increased or decreased. Rate constant for the encapsulation reaction is adjusted for the simulation results to be representative of the experimental results (typically specific weight of carbon (g C/g Ni) vs. time on stream). The system of differential algebraic equations consists of the steady-state equations for all surface intermediates, an algebraic equation of dissolution/segregation, diffusion equation, and the site balance equation. The system has been solved without assuming any rate-determining step or most abundant surface intermediates. Parameter estimation procedures were repeated for the deactivation cycles of regenerated 5 wt% Ni/\gamma-Al_2O_3 catalyst. The basic idea that underlies the model is that every carbon atom will diffuse through the nickel particle and participate in the formation of carbon filaments until the catalyst deactivates. Specific weight of carbon is calculated using the rate of carbon diffusion.

9. Catalyst Regeneration in Fluid Catalytic Cracking

Methods for regenerating H3PW12O40 catalyst in the solvent-free direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas were investigated. Regenerated H3PW12O40 catalyst was then applied to the solvent-free direct preparation of DCP. In the solvent-free direct preparation of DCP, selectivity for DCP over H3PW12O40 catalyst regenerated by method I (recovery of solid H3PW12O40 catalyst by evaporating homogeneous liquidphase product solution) significantly decreased with increasing recycling run, while that over H3PW12O40 catalyst regenerated by method II (regeneration of H3PW12O40 catalyst by oxidative calcination of solid product recovered by method I) was slightly decreased with no significant catalyst deactivation with respect to recycling run. On the other hand, selectivity for DCP over H3PW12O40 catalyst regenerated by method III (regeneration of H3PW12O40 catalyst by recrystallization and subsequent oxidative calcination of solid product recovered by method II) was the same as that over fresh catalyst without any catalyst deactivation with respect to recycling run. Thus, method III was found to be the most efficient method for the regeneration of H3PW12O40 catalyst.

8 - Reactors With Catalyst Decay and Regeneration

Simultaneous hydrogen and aromatics enhancement by obtaining optimum temperature profile and hydrogen removal in naphtha reforming process; a novel theoretical study

Maximum production rate optimization for sulphuric acid decomposition process in tubular plug-flow reactor

In this investigation, a dynamic simulation and optimization for an auto‐thermal dual‐type methanol synthesis reactor was developed in the presence of catalyst deactivation. Theoretical investigation was performed in order to evaluate the performance, optimal operating conditions, and enhancement of methanol production in an auto‐thermal dual‐type methanol reactor. The proposed reactor model was used to simulate, optimize, and compare the performance of a dual‐type methanol reactor with a conventional methanol reactor. An auto‐thermal dual‐type methanol reactor is a shell‐and‐tube heat exchanger reactor in which the first reactor is cooled with cooling water and the second one is cooled with synthesis gas. The proposed model was validated against daily process data measured of a methanol plant recorded for a period of 4 years. Good agreement was achieved. The optimization was achieve by use of genetic algorithms in two steps and the results show there is a favorable profile of methanol production rate along the dual‐type reactor relative to the conventional‐type reactor. Initially, the optimal ratio of reactor lengths and temperature profiles along the reactor were obtained. Then, the approach was followed to get an optimal temperature profile at three periods of operation to maximize production rate. These optimization approaches increased by 4.7 % and 5.8 % additional yield, respectively, throughout 4 years, as catalyst lifetime. Therefore, the performance of the methanol reactor system improves using optimized dual‐type methanol reactor.

In this study, we investigated the effect of potassium on the activity and regeneration of potassium-poisoned SCR catalysts. With the addition of potassium species, the NO conversion rate of the catalysts continuously decreased. After washing the poisoned catalysts with an H2SO4 solution or doping them with CeO2, the activity of the catalysts was improved to different extents. Acid washing almost completely removed the surface potassium species, freeing acidic sites to adsorb NH3, but it also potentially removed some of the active components, such as vanadia. CeO2 doping, on the other hand, added active components. Combining these two methods, the poisoned catalysts were washed with an H2SO4 solution and then doped with 5 wt.% CeO2. It was found that the level of activity could be restored to that of a fresh catalyst, and a conversion rate of over 90% was observed for NO between 300°C and 450°C, as the added CeO2 compensated for the active components lost during SCR reactions. Consequently, the above hybrid method shows high potential for regenerating commercial SCR catalysts.

Efficiently solving multiple objective optimal control problems

Control of a polymerization reactor by fuzzy control method with genetic algorithm

Methane oxidation on alumina supported palladium catalysts: Effect of Pd precursor and solvent

Chapter 8 - Chemical systems with catalyst decay and regeneration

Partial regeneration of an aged commercial automotive catalyst

This work presents a systematic study for obtaining the optimal temperature profile in a continuous plug flow crystallizer (PFC). The proposed PFC consists of multiple segments where the temperature of each segment can be controlled individually. An optimization problem is formulated for a target crystal size distribution (without fines) with the temperature of the segments as decision variables. The results indicate that for the crystallization kinetics considered, dissolution steps are necessary for the reduction of fines due to nucleation. A systematic study on the form of growth and dissolution kinetics suggested that the key factor that determines whether the dissolution steps will be successful in reducing fines, without compromising the final size of the crystals from seed, is the size dependence of the growth and dissolution kinetics. Best fines removal is achieved when the larger crystals grow faster than the smaller ones and the smaller crystals dissolve faster than the larger ones. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4582–4594, 2013