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Reactive Distillation Columns (reactive + distillation_column)

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Chemistry100%

Selected Abstracts

Effects of Liquid Holdup in Condensers on the Start-Up of Reactive Distillation Columns

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2006
H.-X. Wu
Abstract Compared with start-ups in conventional distillation columns, those in reactive distillation (RD) columns are much more time and energy consuming, and generate a large amount of by-products which are not easy to deal with together. For several years, researchers have been trying out different methods to shorten the time required to lower the cost of the start-up. In this work, a rigorous dynamic model in the ChemCAD simulator is applied to model the start-up process for the esterification of ethyl acetate in a reactive distillation column. In the model, two sets of equations are employed: one for the fill-up and heating stage and the other for the equilibration process which follows. In the fill-up and heating stage, fluctuation curves of the reboiler temperatures with respect to time which are similar to those for conventional distillation columns are observed, while in the equilibration process it is found that the increase of the liquid holdup volume in the condenser reduces the time required to reach steady state for the reactive column and decreases the liquid holdup volume in the reboiler at the equilibrium state. This shows that the liquid holdup volume in the condenser has an important effect on the start-up of reactive distillation columns. [source]

Control of a high-purity ethylene glycol reactive distillation column with insights of process dynamics

AICHE JOURNAL, Issue 8 2009
Kejin Huang
Abstract Inventory control is often regarded as less important than product quality control in the operation of reactive and nonreactive distillation columns (i.e., often detuned considerably in control system design). For the high-purity ethylene glycol reactive distillation column, the inventory control of top condenser is, however, an exception and plays actually a crucial role in the stable and effective process operation, reminding the necessity to thoroughly investigate the intricate dynamic mechanism and its complicated implications on control system synthesis and design. In this article, the dynamics of a high-purity ethylene glycol reactive distillation column is examined, and it is found that the complicated dynamics, for example, the nonminimum phase behavior and process nonlinearity, can be suppressed considerably with the tight inventory control of the top condenser. Moreover, an extremely low controllability is detected, implying the potential difficulties in process operation and thus the need of process design modification. In terms of these insights obtained, two control schemes are devised and studied. It is demonstrated that sharp improvement could be acquired in control system performance when the tight inventory control has been implemented in the top condenser. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Effect of number of fractionating trays on reactive distillation performance

AICHE JOURNAL, Issue 12 2000
Muhammad A. Al-Arfaj
Sneesby et al. recently suggested that adding trays in the stripping and rectifying sections of a reactive distillation column can degrade performance. This effect, if true, is not only counterintuitive, but very disturbing because it suggests that the design of reactive distillation columns cannot use conservative estimates of tray numbers, that is, we cannot simply add excess trays, as in conventional distillation. The problem is compounded by the uncertainty in vapor,liquid equilibrium data and tray efficiencies. This implies that developing reactive distillation columns would require extensive experimental work at the pilot-plant and plant stages to find the numbers of stages offering the best performance. Such a scenario would mean long and expensive development programs. This article explores the effect of the number of trays in the rectifying and/or stripping sections of reactive (catalytic) distillation columns. Three reactive distillation systems are used: an ideal hypothetical system, the ETBE system, and the methyl acetate system. Contrary to the published results, it is demonstrated that additional trays do not degrade performance. Two degrees of freedom available in all cases must be carefully chosen for fair comparisons. [source]

Effects of Liquid Holdup in Condensers on the Start-Up of Reactive Distillation Columns

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2006
H.-X. Wu
Abstract Compared with start-ups in conventional distillation columns, those in reactive distillation (RD) columns are much more time and energy consuming, and generate a large amount of by-products which are not easy to deal with together. For several years, researchers have been trying out different methods to shorten the time required to lower the cost of the start-up. In this work, a rigorous dynamic model in the ChemCAD simulator is applied to model the start-up process for the esterification of ethyl acetate in a reactive distillation column. In the model, two sets of equations are employed: one for the fill-up and heating stage and the other for the equilibration process which follows. In the fill-up and heating stage, fluctuation curves of the reboiler temperatures with respect to time which are similar to those for conventional distillation columns are observed, while in the equilibration process it is found that the increase of the liquid holdup volume in the condenser reduces the time required to reach steady state for the reactive column and decreases the liquid holdup volume in the reboiler at the equilibrium state. This shows that the liquid holdup volume in the condenser has an important effect on the start-up of reactive distillation columns. [source]

Using feasible regions to design and optimize reactive distillation columns with ideal VLE

AICHE JOURNAL, Issue 5 2006
Warren R. Hoffmaster
Abstract The design and optimization of reactive distillation columns using feasibility analysis is addressed. Based on the feasible regions identified in previous work, we present two examples to illustrate the benefits of having feasibility information when locating design alternatives for systems with ideal vapor,liquid equilibrium. The examples include a reactive column for the metathesis of 2-pentene and a multifeed reactive column with a constant volatility mixture. In the first example, we use the feasible regions to initialize an optimization-based design strategy. For the second example, we characterize the feasible regions to determine feasible placement strategies for side streams and reactive stages. The design insights gained from feasibility analysis are highlighted for each example. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Interaction of separation and reactive stages on ETBE reactive distillation columns

AICHE JOURNAL, Issue 3 2004
Budi H. Bisowarno
Abstract Reactive distillation is a favorable alternative to conventional series of reactor-distillation processes for ether productions. However, the design of such columns is complicated due to the interaction between vapor-liquid equilibrium and reaction rates. There are conflicting reports on whether adding excessive separation stages degrade the column performance. A comparison is made of several designs of single and double feed reactive distillation columns for ETBE production to investigate the effects of separation and reaction stages on the overall performance. The explanations are presented using simulation results, whose mathematical models are written in the Aspen Plus environment. The results confirm that a conservative approach by adding extra separation and reaction stages can be applied to reactive distillation design. However, output multiplicity may be observed for longer column and should be considered in the early design phase. © 2004 American Institute of Chemical Engineers AIChE J, 50: 646,653, 2004 [source]

Graphical design applied to MTBE and methyl acetate reactive distillation processes

AICHE JOURNAL, Issue 6 2001
Jae W. Lee
Graphical tray-by-tray methods for reactive distillation columns we developed previously are extended to study two industrial processes: MTBE production and methyl acetate production. As both processes involve four components, projection was used to obtain ternary diagrams by ignoring the inert (n-butane) for MTBE production and by projecting onto planes of constant acetic acid concentrations for methyl acetate production. These projected methods clearly explain the placing that industry uses for the reaction zones in these processes. Further, it can be visualized why there is an optimum reflux ratio for the methyl acetate process and a value can be quantitatively predicted for it that lies within the range the literature reports. [source]

Effect of number of fractionating trays on reactive distillation performance

AICHE JOURNAL, Issue 12 2000
Muhammad A. Al-Arfaj
Sneesby et al. recently suggested that adding trays in the stripping and rectifying sections of a reactive distillation column can degrade performance. This effect, if true, is not only counterintuitive, but very disturbing because it suggests that the design of reactive distillation columns cannot use conservative estimates of tray numbers, that is, we cannot simply add excess trays, as in conventional distillation. The problem is compounded by the uncertainty in vapor,liquid equilibrium data and tray efficiencies. This implies that developing reactive distillation columns would require extensive experimental work at the pilot-plant and plant stages to find the numbers of stages offering the best performance. Such a scenario would mean long and expensive development programs. This article explores the effect of the number of trays in the rectifying and/or stripping sections of reactive (catalytic) distillation columns. Three reactive distillation systems are used: an ideal hypothetical system, the ETBE system, and the methyl acetate system. Contrary to the published results, it is demonstrated that additional trays do not degrade performance. Two degrees of freedom available in all cases must be carefully chosen for fair comparisons. [source]

Effects of Liquid Holdup in Condensers on the Start-Up of Reactive Distillation Columns

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2006
H.-X. Wu
Abstract Compared with start-ups in conventional distillation columns, those in reactive distillation (RD) columns are much more time and energy consuming, and generate a large amount of by-products which are not easy to deal with together. For several years, researchers have been trying out different methods to shorten the time required to lower the cost of the start-up. In this work, a rigorous dynamic model in the ChemCAD simulator is applied to model the start-up process for the esterification of ethyl acetate in a reactive distillation column. In the model, two sets of equations are employed: one for the fill-up and heating stage and the other for the equilibration process which follows. In the fill-up and heating stage, fluctuation curves of the reboiler temperatures with respect to time which are similar to those for conventional distillation columns are observed, while in the equilibration process it is found that the increase of the liquid holdup volume in the condenser reduces the time required to reach steady state for the reactive column and decreases the liquid holdup volume in the reboiler at the equilibrium state. This shows that the liquid holdup volume in the condenser has an important effect on the start-up of reactive distillation columns. [source]