K. D. Mohl

Steady-state multiplicities in reactive distillation columns for the production of fuel ethers MTBE and TAME: theoretical analysis and experimental verification

In this contribution, the nonlinear dynamic behaviour of reactive distillation columns for the production of MTBE and TAME is studied. The focus is on steady-state multiplicity and a rigorous bifurcation analysis of pilot plant reactive distillation columns for both processes is presented. The different sources and physical causes for the existence of multiple steady-states in MTBE and TAME synthesis are discussed. Further, a rigorous experimental verification of steady-state multiplicity in a pilot plant reactive distillation column for the production of TAME is presented. Finally, some remarks on the implications of multiple steady-states on column operation are made.

Nonlinear computation in DIVA — methods and applications

Methods for one-parameter continuation and stability analysis of periodic solutions as well as two-parameter continuation of Hopf and limit bifurcation points have been added to the dynamic flowsheet simulation environment DIVA. They are specially tailored for large sparse systems of differential algebraic equations with arbitrary structural properties usually arising in dynamic flowsheet simulation of chemical processes and plants. The application of these methods combined with the other capabilities of such an integrated tool for nonlinear system analysis is demonstrated for two different types of processes. The first is the so-called circulation-loop reactor, which has been used for catalytic combustion of waste air. Through periodic operation of the reactor, abatement of small amounts of volatile organic compounds (VOCs) in waste air is possible autothermally or with minimum supply of energy. Control strategies are studied for extending the region of desired periodic operating points, when the amount of VOCs is too small for autonomous periodic operation. The second application is concerned with the nonlinear dynamic behaviour of reactive distillation processes for the production of fuel ethers MTBE and TAME. In particular, the existence of multiple steady states is analyzed for the practical important case, when pre-reaction is carried out prior to the reactive distillation column. Further, these results are compared with the case without pre-reaction and a physical interpretation is given.

Nonlinear dynamics of reactive distillation processes for the production of fuel ethers

A rigorous numerical bifurcation and stability analysis of reactive distillation processes for the production of fuel ethers MTBE and TAME is presented. The bifurcation behaviour is studied in terms of operating conditions such as reflux ratio R and bottom flow rate B or the heating rate Q of the reboiler, respectively. Further domains of attraction and the transient behaviour towards different stable steady states are studied exemplarily using dynamic simulation. From the size and location of the multiplicity regions in the parameter space of the input variables some conclusions are drawn for process operation.

Multiple steady states in a reactive distillation column for the production of the fuel ether TAME. I. Theoretical analysis

Both Part I and Part II of this paper demonstrate how suitable operating conditions for an experimental verification for the TAME process were determined by the close interaction of theoretical analysis and experimental work. Afterwards dynamic simulation was used to develop suitable start-up procedures for the different steady states. Part I concentrates on the theoretical analysis, while Part II covers mainly the experimental results.

A theoretical study of kinetic instabilities in catalytic distillation processes: influence of transport limitations inside the catalyst

Abstract The influence of transport limitations on kinetic instabilities in heterogeneously catalyzed reactive distillation processes is analyzed by means of two different mathematical models with finite and infinite transport rates inside the porous catalyst. Different system configurations, such as a single catalyst pellet, an isothermal CSTR, and one-tray, multi-tray as well as packed reactive distillation columns are considered. This procedure allows detailed insight into the different sources and mechanisms leading to complex nonlinear behavior in catalytic distillation columns. As an example the well-known MTBE process is considered. In contrast to previous studies, focus is on the kinetic regime of the chemical reaction at column pressures of 6– 7 bar .

Optimization of a reactor network for ethylene glycol synthesis — An algorithmic approach*

Abstract This contribution is concerned with the energy optimal process design for ethylene glycol synthesis. A systematic approach is developed based on the optimization of a general network model. A rigorous non-isothermal model for different network constituents is derived. These constituents are a two-phase reactor condenser element and several mixer/splitters with which the elements are connected to form the network superstructure. As one special case the resulting superstructure includes a process scheme commonly used in industries where reaction and separation are carried out in different devices. A second special case is a reactive distillation column recently proposed in literature. The general reactor network model is optimized by nonlinear programming (NLP) methods in order to obtain an energy minimal network configuration.

Object-oriented modeling of distillation processes

Abstract The process modeling tool ProMoT supports the object-oriented and equation-based modeling of chemical processes for the process simulation environment Diva . This contribution demonstrates the modeling methodology of ProMoT and the advantages of object-oriented modeling by looking at the design of a knowledge base containing reusable modeling entities for modeling (reactive) distillation processes.

MTBE decomposition in a reactive distillation column

MTBE decomposition in reactive distillation columns is investigated based on numerical simulations. Special emphasis is on the undesired side reactions. Quasi-homogeneous as well as heterogeneous column models are applied for a packed column. In the latter, the multi-component intra-particle mass transport phenomena are accounted for. Continuation methods are used to study the influence of the design and operating parameters in order to determine optimal conditions. One finding is that the catalyst holdup should be very low in order to fully convert MTBE with high selectivity into the desired products isobutene and methanol. The results from the heterogeneous model illustrate the role of mass transport inside the catalyst particles, especially at larger size and higher pressure.

Nonlinear Analysis of gPROMS Models Using DIVA as via a CAPE ESO interface

Abstract The CAPE ESO interface of the process simulator gPROMS is used to pass model information to numerical methods contained in the simulation environment DIVA. By the interface, algorithms for the continuation of stable and unstable steady state and periodic solutions can be applied directly to gPROMS models. The use of the interface is illustrated by a detailed nonlinear model of an industrial reactive distillation column.