Ethanol dehydration process

Although benzene is a more favorable entrainer for this separation or similar ethanol dehydration process, its use is prohibited because of the carcinogenic nature of this entrainer. Having insight into what constitutes a good entrainer will help to identify other potential candidates as entrainers. 

The production of ethylene by dehydration of ethanol is a proven technology and was demonstrated and implanented on large scale (Winter, 1976). Braskem started a full-scale plant in Brazil in 2010 (Braskem, 2012). The process consists of a dehydration reactor and several subsequent purification steps in order to obtain polymer-grade ethylene (composition 99.95 wt% ethylene, 0.05 wt% ethane, 5ppm CO and lOppm CO (Kochar et al., 1981)). Figure 4.6 iUustrates the ethanol dehydration process investigated in this study and lists the input data used for process simulation. 

The assumed running time of both the ethanol and the ethanol dehydration plants is 8500h/year. 73% of the total heat used in the ethanol dehydration process is consumed by the ethylene reactors which are by far the most energy-intensive part of the process. The reactors operate at high temperature (390-450 C) and therefore have to be heated by direct... 

Figure 4.8 CCC of the ethanol dehydration process direct steam injection of 25 MW steam to the ethylene reactor is considered a process requirement and therefore not included...

The GCC of the ethanol dehydration process is shown in Figure 4.8. The minimum heating and cooling demands are 19 and 48MW. The processes pinch temperature is 174°C and therefore considerably higher than the pinch temperature of the ethanol production process (96°C). The GCC below the pinch point is relatively flat and indicates large amounts... 

In order to illustrate heat integration opportunities and thus also to estimate the utility savings potential, a background/foreground (BF) analysis of the two processes was performed. Figure 4.9 shows the BF analysis of the combined processes. It can be seen that there is an opportunity to recover 44.5 MW of excess heat in the ethanol dehydration process and deliver it to the ethanol production process. As mentioned previously, most of the excess heat at higher temperatures originates from the ethylene reactor effluent. The hot ethylene reactor effluent stream is cooled from 428 to 84 C and has a relatively... 

Figure 4.9 Background/foreground analysis of the ethanol production and ethanol dehydration process direct delivery of ethanol between the processes is accounted for in the stream data...

Fowler CB, O Leary TJ, Mason JT. Modeling formalin fixation and histological processing with bovine ribonuclease A effects of ethanol dehydration on reversal of formaldehyde-induced cross-links. Lab. Invest. 2008 88 785-791. 

Most of the early solvent dehydration systems were installed for ethanol dehydration. More recently pervaporation has been applied to dehydration of other solvents, particularly isopropanol used as a cleaning solvent. Dehydration of other solvents, including glycols, acetone and methylene chloride, has been considered. Schematics of pervaporation processes for these separations are shown in Figure 9.13. 

Black, C., "Distillation Modelling of Ethanol Recovery and Dehydration Processes for Ethanol and Gasohol," Chem. Eng. 

The dehydrogenation of ethanol over copper catalysts is not complete at 300° C. when moderate times of contact are used but if the temperature is raised to 350° C. or higher, secondary reactions become more and more evident. At temperatures above 350° C., copper catalysts begin to activate the decomposition of acetaldehyde to methane and carbon monoxide, to induce polymerization of the aldehyde, to cause dehydration processes to set in, to cause hydrogenation of the ethylene, and, in general, to promote secondary decompositions and condensations which complicate the product and destroy the activity of the catalyst. Hence, for the production of aldehydes and ketones it is desirable to use moderate temperatures of about 300° C. and to obtain maximum yields from the decomposition rather than maximum decomposition of alcohol per pass over the catalyst. 

Hu, Y. C, Unconvenrional olefin processes. Part 2 Ethanol dehydration . Hydrocarbon Processors. 62 (4) 113-116(1983)... 

---