아스펜 모사기를 이용한 MEK 공정의 최적 설계

박 영 철 , 이 태 용

대전광역시 유성구 구성동 373-1 (우) 305-701

한국과학기술원 화학공학과

Optimal Design of MEK(Methyl Ethyl Ketone) Process Using Aspen Plus Steady-State Simulator

Young Cheol Park and Tai-yong Lee

Department of Chemical  Engineering

Korea Advanced Institute of  Science and Technology

373-1, Kusong-dong, Yusung-gu, Taejon, Korea, 305-701

Introduction

MEK process which is based on The Manufacture of Methyl Ethyl Ketone from 2-Butanol(SBA) written by D.G.Austin and G.V. Jeffreys[1] is simulated by Aspen Plus. There are several difficulties such as modeling of catalyst tubular reactor, material loss problem and convergence to perform simulation. In this study, Langmuir-Hinshelwood-Hougen-Watson(LHHW) model is used to simulate catalyst tubular reactor, In-line Fortran is used to solve material loss problem, and tearing streams and reordering calculation sequence are used to get a  good convergence. Finally, to perform optimal design of this process, Flowsheeting options such as Design Specification, Optimization, and Sensitivity Analysis in Aspen Plus are used.

Simulation by Aspen Plus

Based on the process design[1], PFD(Process Flow Diagram) is presented in Fig 1. There are major 8 blocks that is, Reactor and Vaporiser, Condenser and Flash column, Absorption column, Extract column, Solvent recovery still, and MEK product still and 4 recycle streams. To simulate this process, there are several techniques to overcome simulation difficulties.

First one is LHHW model which is used to implement catalyst reactor. LHHW (Langmuir-Hinshelwood-Hougen-Watson) kinetics for the reactor model expressed as

In this process, reaction rate of dehydrogenation reaction is[3]

where A is 2-butanol, K is MEK, and H is hydrogen. To implement LHHW model, several parameters are needed and the value is converted to Aspen format.

Second one is material loss problem in which the component water between the absorption column and the extraction column and the component TCE between the extraction column and the solvent recovery still since those components were out in the stream lines, 18, 3 for water and raffinat, 20 for TCE. Thus, the PFD resolved this problem is shown in Fig 2. In this process flow diagram, there are two mixers to make up water and TCE using In-line Fortran.

Third one is tearing streams and reordering computational sequence. 4 recycle streams which are product recycle stream between reactor and vaporiser, absorbent recycle stream between absorption column and extract column, solvent recycle stream between extract column and solvent recovery still, and 2-butanol recycle stream between feed storage tank and MEK product still should be tear streams. Tear streams generally need initial value to initiate simulation, thus put into initial value at absorbent, solvent, and 2-butanol recycle streams. To have a good convergence, there should be adequate simulation sequence. In this process, a new simulation sequence having a good convergence.

Optimal Design Using Flowsheeting Options

To perform optimal design, folwsheeting options[5] are very useful. Especially, Design Specification option acts like a simple feedback control and Optimization is used to maximize or minimize objective function with several constraints. In this study, 6 major design spec are present[2]. These 6 design spec are put into the Design Specification option and each Design Spec has manipulated variable whose value is decided by simulation. Based on Design Spec results, Optimization is performed to maximize the folwrate of product stream, especially, MEK component. The objective function and constraints are expressed as

Max {flowrates of MEK component in product stream}

s.t.   6 design specs

absorbentL ≤ absorbent ≤ absorbentU

solventL ≤ solvent ≤ solventU

In this formulation, the maximum MEK flowrate can be obtained and the absorbent and solvent flowrates are also determined. The maximized objective function and the manipulated variables are shown in Table 1.

Results and Discussion

The simulation results are tabulated in Table 2. The results are  slightly different from the values introduced in The Manufacture of Methyl Ethyl Ketone from 2-Butanol written by D.G.Austin and G.V. Jeffreys[1], but simulation results of each unit satisfy material balance and the process design specifications. For each design specification, each manipulated variable such as reflux ratio, solvent or absorbent flowrates is calculated during simulation. The optimization result shows that the change of design variable and absorbent and solvent flowrates make the final product rate maximized. After optimization, sensitivity analysis can be used to verify if the solution to a design specification lies within the range of the manipulated variable.

Conclusions

In the present study, the process simulation results using Aspen Plus show that it is possible to produce MEK more than 1×107kg/year and the calculated design specs of each unit can be accepted. Through Flowsheeting options, optimal design structure and maximum product flowrate can be obtained.

Acknowledgement

This work was also partially supported by the Brain Korea 21 Project.

References

[1] D.G. Austin and G.V.Jeffreys "The Manufacture of Methyl Ethyl Ketone from 2-Butanol" Warwick (1979).

[2] Young Cheol Park, Tai-youg Lee "Computer-Aided Synthesis of MEK Process" The 12th Symposium on Chemical Engineering Chungnam-Kyushu (1999)

[3] Joseph J. Perona and George Thodos "Reaction Konetic Studies: Catalytic Dehydrogenation of Sec-butyl Alcohol to Methyl Ethyl Ketone" AIChE journal (1957)

[4] Copper A.R. & G.V.Jefferys "Chemical Kinetics and Reactor Design" Prentice Hall (1973).

[5] Aspen Plus 10 User Guide Volume 1, Volume 2

Fig 1. Process Flow Diagram

Table 1. Optimized values

Fig 2. In-Line Fortran

Table 2. MEK product still      inlet & outlet streams