ETBE Reactors

Owing to thermodynamic and kinetic constraints it is very important in the ETBE process to choose the right reactor. 

Adiabatic and tubular reactors are the standard solutions employed as front-end reactor (the first reactor where most of the reaction takes place). 

Up flow operation makes the pressure drop across the reactor almost negligible and avoids catalyst plugging, making catalyst unloading even easier. 

WCTR couples all the advantages of a drum reactor in terms of catalyst loading and unloading with the advantages of a tubular reactor with respect to minimum catalyst inventory and optimum temperature control. 

This different temperature profile also has an impact on by-product production the lower mean temperature achievable in WCTR allows us to maintain at lower extent by-product formation. 

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The most important application of RD today seems to be the production of ethers such as methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME), which are widely used as modem gasoline components. Figure 7, upper part, shows a traditional process for MTBE production, which is a strongly exothermic reaction. The disadvantages of that process can be avoided if the reaction and separation take place within the same zone of the reactor (Figure 7, lower part). 

The reactor inlet temperature ranges from 50°C at start-of-run to about 65°C at end-of-run conditions. One important feature of the two-stage system is that the catalyst can be replaced in each reactor separately, without shutting down the ETBE unit. 

ETBE is recovered as the bottoms product of the distillation unit. The ethanol-rich C4 distillate is sent to the ethanol recovery section. Water is used to extract excess ethanol and recycle it back to process. At the top of the ethanol/water separation column, an ethanol/water azeotrope is recycled to the reactor section. The isobutene-depleted C4 stream may be sent to a raffinate stripper or to a molsieve-based unit to remove oxygenates such as DEE, ETBE, ethanol and tert-butanol. 

Kinetic tests were carried out In a fixed-bed tubular reactor described elsewhere (ref.10). Reaction conditions were catalyst weight = 5 g total pressure 3 MPa molar ratio Kj/ethylbenzene - 10 liquid space velocity > 3 h and reaction temperature > 523 K. Liquid ethylbenzene (ETB) was diluted with decal in (70 wtX) and 100 ppm of thiophene were added. Reactants and products were analyzed by GLC. 

ETBE is produced by the liquid-phase addition of ethanol (EtOH) to isobutene (IB) in presence of an acid catalyst. Since the reaction is exothermic and limited by the chemical equilibrium, the reactor outlet temperature is maintained as low as allowed by the catalyst activity in order to maximize the isobutene conversion. Operating temperatures range between 40 and 80 °C. 

Figure 3.33 shows a schematic of the CDTech MTBE/ETBE/TAME process. This is essentially the same as the CDTech MTBE process presented earlier. The process is unique in the sense of using a boiling point reactor and catalytic distillation (CD) [61]. The C4 feed and methanol is fed to the boiling point reactor (1). This is a fixed-bed downflow adiabatic reactor, in which the liquid is heated to its boiling point by the heat of reaction and... 

Figure 3.32 Flowsheet of the ARCO MTBE/ETBE/TAME process. (1) preheater, (2,3) fixed-bed adiabatic reactors, (4) distillation column, (5) reactor, (6) alcohol stripper. Source. [9].

Figure 3.33 Flowsheet of the CDTech MTBE/ETBE/TAME process. (1) boiling point reactor, (2) CD column, (3) extraction column, (4) methanol recovery column. Source [61].

Literature investigations were used in order to address the six listed challenges these are considered to be some of the most important aspects related to the bioremoval of MTBE in reactors. The focus is on the use of aerobic bioreactors for aqueous phase MTBE removal by direct metabolism. The discussions on cometabolism are confined to its own section. The concepts and information provided are mainly applicable to the ex situ remediation of MTBE contaminated groundwater. The ideas presented, however, can also be applied to MTBE removal in drinking water treatment or industrial applications. Most of the discussions are equally valuable to TBA and other ethers used as fuel oxygenates. These are for example, ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE). 

Sutherland et al. [37] observed in a continuous plug flow reactor that other ethers (ETBE, DIPE, and TAME) are more efficiently removed than MTBE. Only tBA removal proved to be less efficient. These investigations resulted in lower calculated unit treatment costs for the alternative ethers (up to 64%) but higher costs for the treatment of fBA. 

Description A typical MTBE/ETBE unit using FCC cut is based on a single-stage scheme, with a tubular (1) and an adiabatic (2) reactor. The front-end reactor uses the proprietary water-cooled tubular reactor (WCTR). The WCTR Is a very flexible reactor and can treat all C cuts on a once-through basis. 

Kiatkittipong et al. (2002) investigated a PV membrane reactor for the synthesis of ethyl icri-butyl ether (ETBE) from a liquid phase reaction between EtOH and TEA. Supported p-zeolite and PVA membrane were used as catalyst and as membrane in the reactor, respectively. The permeation studies of water-EtOH binary system revealed that the membrane worked effectively for water removal for the mixtures containing water lower than 62 mol%. The permeation studies of quaternary mixtures (water-EtOH-TBA-ETBE) were performed at three temperature levels of 323, 333, and 343 K. It was found that the manbrane was preferentially permeable to water. 

ETBE Process. An article by Sneesby et al. provides a description of the conventional ETBE process. There are two reactors in series, the first operating at 90 °C and the second at 50-60 °C. The lower temperature in the second reactor gives a higher equilibrium constant because the reaction of ethanol and isobutene to produce ETBE is exothermic. 

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