Lumping procedures in detailed kinetic modeling of gasification, pyrolysis, partial oxidation and combustion of hydrocarbon mixtures

Lignocellulosic biofuels have a tremendous potential to reduce problems caused by our dependence on fossil fuels. The current roadblock with biofuels is the lack of economical conversion technologies. Heterogeneous catalysis offers immense potential in helping to make lignocellulosic biofuels a commercial reality. In this article we discuss the central role of heterogeneous catalysis in biomass conversion. We review the science of catalysis and the different routes to make biofuels. During the last several decades multiple new spectroscopic, theoretical, and synthesis tools are available that allow us to study catalysis at a molecular level. These new tools will allow us to rapidly develop new catalytic processes for the production of cost-efficient lignocellulosic biofuels.

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The critical role of heterogeneous catalysis in lignocellulosic biomass conversion

Over the course of the commercial fluid catalytic cracking (FCC), catalyst deactivation occurs both reversibly, as a result of side reactions that eventually yields coke, and irreversibly, due to contaminants present in the feedstock or to the dealumination of the zeolite catalyst component. Herein, we discuss the deactivation of HY zeolite and FCC catalysts from a fundamental as well as an applied point of view. Aspects related to the various causes of FCC catalysts (and additives) deactivation under industrial conditions are also summarized.

Deactivation of FCC catalysts

Detailed modeling of complex reaction systems is becoming increasingly important in the development, analysis, design, and control of chemical reaction processes. For industrial processes, complete incorporation of the chemistry into process models facilitates the minimization of byproduct and pollutant formation, increased efficiency, and improved product quality. Processes that involve complex reaction networks include a variety of noncatalytic and homogeneous or heterogeneous catalytic processes (such as fluid catalytic cracking, combustion, chemical vapor deposition, and alkylation). For some systems, large sets of relevant reactions have been identified for use in simulations.1-3 For others, the availability of advanced computing environments has enabled the automated generation of reaction networks and their models, based on computational descriptions of the reaction types occurring in the system.4-6 The use of such complex models is hindered by two obstacles. First, because of their sheer size and the presence of multiple time scales, these models are difficult to solve. Second, the models contain large numbers of uncertain (and sometimes unknown) kinetic parameters; regression to determine the parameters of complex nonlinear models is both difficult and unreliable, and the sensitivity of simulations to parameter uncertainties cannot be easily ascertained. Furthermore, for the purpose of gaining insights into the reaction system’s behavior, it is usually preferable to obtain simpler models that bring out the key features and components of the system. For these reasons, model simplification and order reduction are becoming central problems in the study of complex reaction systems. The simulation, monitoring, and control of a complex chemical process benefit from the derivation of accurate and reliable reduced models tailored to particular process modeling tasks. Model simplification is directly linked to identification of key reactions and sets of species that give valuable insights into the behavior of the network and how it may be influenced. Advanced control schemes such as model predictive control7 or multiple model adaptive control8 must be based on selecting appropriate reduced models and tracking key sets of species. Ideally, a model order reduction algorithm should have broad applicability, enable analysis at several levels of detail, and provide an assessment of the modeling error.

http://depa.fquim.unam.mx/amyd//archivero/mODELOSDEcINETICA_3417.pdf

Simplification of mathematical models of chemical reaction systems

Process for gas-phase polymerization carried out in two interconnected polymerization zones, to which one or more α-olefins CH2=CHR are fed in the presence of catalyst under reaction conditions and from which the polymer product is discharged. The process is characterized in that the growing polymer flows through a first polymerization zone under fast fluidization conditions, leaves said first zone and enters a second polymerization zone through which it flows in a densified form under the action of gravity, leaves said second zone and is reintroduced into the first polymerization zone, thus establishing a circulation of polymer around the two polymerization zones. The novel process allows olefins to be polymerized in the gas phase with high productivity per unit volume of the reactor without incurring the problems of the fluidized-bed technologies of the known state of the art.

Process and apparatus for the gas-phase polymerization of alpha-olefins

A predictive kinetic model has been developed for fluid catalytic cracking (FCC). The kinetic scheme involves lumped species consisting of paraffins, naphthenes, aromatic rings, and aromatic substituent groups in light and heavy fuel oil fractions. The kinetic model also incorporates the effect of nitrogen poisoning, aromatic ring adsorption, and time dependent catalyst decay. The rate constants for these lumped species are invariant with respect to charge stock composition. The predictive capabilities of the model have been verified for wide ranges of charge stocks and process conditions.

A lumping and reaction scheme for catalytic cracking

A fluid catalytic cracking (FCC) process and apparatus using a riser and a reactor for cracking of petroleum feeds in the presence of a catalyst and a regenerator for regenerating the spent catalyst are improved by providing a downflow riser. The downflow riser assures uniform distribution of the catalyst throughout the feed, decreases contact time of the catalyst with the feed and decreases the amount of coke made in the process.

FCC Reactor with a downflow reactor riser

A hydrocarbon conversion-catalyst regeneration operation is described which relies upon a dense fluid catalyst bed superimposed by a dispersed catalyst phase operation to effect elevated temperature regeneration of the catalyst providing low CO levels less than 0.15 mol percent in the flue gas by mixing regenerated catalyst with spent catalyst to obtain an initial mix temperature of at least 1175° F. before contact with oxygen containing regeneration gas. The ratio of regenerated to spent catalyst is restricted to within the range of 0.5 to 1.5 and the oxygen content through the dense and dispersed catalyst phase is selected to provide a discharged dispersed catalyst phase temperature of at least 1350° F.

Method and system for regenerating fluidizable catalyst particles

In the fluid catalytic cracking process, improved adaptive behavior of the catalyst section with the regenerator operating in the complete CO-burning mode is achieved by including, as elements of control, variable preheat of the air feed and variable recycle of regenerated catalyst to spent catalyst. In response to excursions of the regenerated catalyst temperature, such as would be caused by change of feedstock, the air preheat temperature and recycle ratio are altered in a direction to restore the regenerated catalyst temperature to a predetermined value. The improved control system extends the useful control range, and it also diminishes counterproductive changes in severity induced by disturbances such as change of feedstock quality.

Fcc catalyst section control

In a fluid catalytic cracking (FCC) process and apparatus, the heat balance between the reactor and the regenerator of the FCC operation is partially uncoupled by transferring at least a portion of thermal energy from the reactor vessel downflow riser to the regenerator vessel. The transfer of thermal energy results in a higher regenerating temperature. The thermal energy is recirculated to the upstream section of the downflow reactor riser through a regenerated catalyst having higher temperature. Consequently, the outlet of the reactor vessel is maintained at a substantially constant temperature (e.g., 1000° F.) and the rate of conversion of the oil feed and the octane number of gasoline produced in the process are increased.

Benjamin Gross

Papers

A lumping and reaction scheme for catalytic cracking

FCC Reactor with a downflow reactor riser

Method and system for regenerating fluidizable catalyst particles

Fcc catalyst section control

Heat balance in FCC process and apparatus with downflow reactor riser