MEK 공정의 컴퓨터-원용 합성

박 영 철 , 이 태 용

대전광역시 유성구 구성동 373-1 (우) 305-701

한국과학기술원 화학공학과

Computer-Aided Synthesis of MEK(Methyl Ethyl Ketone) Process

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

Rigorous process simulation has several advantages even though some other short-cut prediction methods are also available. First, it reduces plant design time; thus, it allows designer to quickly test various plant configurations. Second, it enables the designer to produce reliable design: it answers what if questions, determines optimal process conditions within given constraints, and assists in locating the constraining parts of a process. One of the powerful process simulation tools is Aspen Plus, and especially, it has several advantages to implement processes which is not present in Aspen Plus using user model by External Fortran or In-line Fortran. In this study, In-line Fortran is used to make up material loss problems in MEK synthesis process which was 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 as a case study.

Conceptual design of MEK manufacturing process

In this case study, the design objective is to produce 1107kg per annum of MEK. MFD can be constructed based on overall material balance. The material balance of each unit was calculated based on the hourly production rate and 8000h will be taken as the on stream time. Allowing 8.0% for spillage and other process losses the hourly production rate of MEK will be 1350kg/h. Total SBA consumed is 1401.14kg/h and the recycle rate will be 156.10kg/h.

(1) Reactor : In this case study, dehydrogenation from SBA was selected as a reaction type. Based on the general considerations for the design of the reactor[2], it was concluded that a shell-and-tube type reactor was the most suitable for the duty envisaged. Furthermore, it was decided that the heat of reaction would be supplied by flue gas and in order to achieve 90% conversion, the exit temperature must not fall below 400C.

(2) Condenser : The products of reaction are to be discharged from the reactor at 370C and passed to the shell side of the thermo-syphon reboiler type evaporator to the feed. The vapor temperature of the reaction products has been reduced to 125C, a suitable temperature to enter the condenser. The vapors enter the condenser at 125C and at a pressure of 1.0bar. They will be cooled until more than 80% of the condensables have been removed from the vapor. It is proposed to install a horizontal single pass shell-side, single pass tube-side heat exchanger operating under counter-current flow conditions.

(3) Absorption column : The gas phase discharged from the condenser at 62.7C is to be treated in an absorption column with a very dilute aqueous solution of MEK recycled from the extraction column. The unit is to be designed to absorb 98% by weight of the MEK and nearly all the alcohol.

(4) Solvent extraction unit : The effluent liquor discharged from the gas absorption column will be treated with 1,1,2-trichloroethane(TCE) to extract the MEK and SBA. The extract phase containing the MEK and SBA will be distilled to recover the products and the solvent will be recycled to the extraction column. All the MEK cannot be extracted from the aqueous solution, but examination of the phase diagram and the distribution diagram shows that it is possible to recover sufficient MEK to leave final raffinate containing only 0.5% weight MEK. Based on this idea, solvent rate is determined by the optimum solvent/feed ratio and the value is 898kg/h. The extracted phase will be discharged to a solvent recovery still and it contains four components. However, the amount of water and SBA present is so small that these will not be able to exert any affect on the transport processes occurring in the solvent recovery still. Therefore the design of this unit will be based on the binary mixture MEK/TCE and the equilibrium diagram for this binary was evaluated from Raoults law.

(5) Production distillation unit : The product distillation unit will be fed with a MEK/SBA mixture obtained from the condensate from the condenser and from the distillate of the solvent recovery still of the extraction plant. These two streams are to be mixed in an intermediate storage holding tank and then fed to the product distillation unit. This mixture is to be distilled to produce a top product containing 99.0% weight MEK and a bottom product containing 99.0% weight SBA. The SBA will be recycled and mixed with the feed to the reactor.

Simulation by Aspen Plus

Based on the above process design, PFD(Process Flow Diagram) is presented in Fig 1. However, there has been 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. It follows three steps; first, define Fortran variables, second, enter executable Fortran statements, third, choose Fortran block execution sequence. In this case, "Use read/write variables" is used to activate In-line Fortran during simulation. Thus, the amount of water at stream 18 and 3 is read and then written at stream AMAKEUP. The amount of TCE is also determined by the same way as above. Through complementing In-line Fortran, the MEK synthesis process is simulated by Aspen Plus.

Results and Discussion

The simulation results are tabulated in Table 1. The production rate of MEK is 1353.56kg/h and SBA in the recylcle stream is 158.78kg/h.  Those 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 specs. However, the problem present this simulation is product purity; that is, a small quantity of TCE, toxic material, is in the final product. Thus, several distillation columns are needed to get rid of TCE from the final product.

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. Most of all, material loss problem at recycle streams can be implemented by Aspen Plus using In-line Fortran.

Acknowledgement

This work was supported by the Korea Science and Engineering Foundation (KOSEF) through the Automation  Research Center at POSTECH.

References

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

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

Fig 1. MEK Synthesis Process Flow Diagram

Fig 2. Resolved PFD using In-line Fortran          Table 1. Simulation Results