Erik Stein

Reactive separation of isobutene from C4 crack fractions by catalytic distillation processes

Reactive distillation is a hybrid process where chemical reaction and distillative separation are performed in a single equipment. Even though reactive distillation could increase the selectivity of the desired product by the selective reaction this is not always true as shown in this work. A study on the MTBE reaction system using two coupled reactive distillation columns to separate a C4 crack mixture is carried out, where methanol acts as reactive entrainer and MTBE is the intermediate product. In the first column, isobutene and methanol react to form MTBE hence separating the inert C4 component, while in the second column MTBE splits back to methanol and isobutene. Methanol is recycled back to the MTBE formation column and isobutene is obtained as a product. This coupled process with direct recycle of methanol is possible only if no side reactions occur. When the side reactions are taken into account, byproducts such as diisobutene, dimethyl ether and water will be produced so that higher purity methanol can not be obtained at the bottom of the splitting column. The outlet of the splitting column must be firstly separated rather than being recycled directly to the formation column. Moreover, an attempt has been made to show how the selectivity of the desired product isobutene can be critically influenced by the operating parameters such as the reflux ratio. If the reflux ratio increases, a high quantity of diisobutene and dimethyl ether will be obtained which seriously affects the selectivity of isobutene. The influence of operating parameters is investigated by using a continuation method, which shows that bifurcation behavior can appear in both MTBE formation and decomposition process.

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.

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.