17.2.3 Technical questions

1. What is Dowtherm ?

Ans: Dowtherm is an organic liquid that can attain to temperatures upto 300°C. These are special fluids used instead of steam/water. In this example, the operating temperature is about 250 - 300°C and therefore usage of Dowtherm fluid is perfect.

2. In what way compression is beneficial to the absorption ?

Ans: It is a known fact that absorption is most favoured at low temperature and high pressure. Therefore, compression of the cooled product gases will be very beneficial to maximize the dissolution of ethylene oxide in the water. Ofcourse, along with ethylene oxide other light ends and heavy ends also dissolve in water and we have no control over that.

3. Why again another compressor is used before the stripper ?

Ans: The second compressor aids to enhance the boiling points of the mixtures. Thereby, water can be used as a cooling fluid in the distillation columns, as the boiling point of the products is enhanced by compression. In this regard, it should be noted that ethylene oxide has a boiling point of 10.7°C which can be drastically enhanced by compression to 4 – 5 atms.

4.  Why ethylene and air are separately compressed ?

Ans: This is due to the danger of generating an explosive mixture during compression step of the mixture.

5. What process modifications are possible for the flowsheet ?

• • Using a fluidized bed instead of packed bed reactor

• Using oxygen instead of air

6. Discuss the energy integration capacity of the process ?

Ans: In this process, the heat integration drastically reduced process steam requirements. Steam is only required in the strippers and fractionators. This steam can be generated using waste heat recovery units using dowtherm fluid as the hot fluid to generate the steam. Thus in this process, it is observed that for 1 ton of ethylene oxide produced, only 0.1 ton of steam is required. This is all possible due to significant heat integration in the process.