ETBE Control

The two fresh feedstreams to the column arc ethanol and a C4 stream containing reactive isobutene and nomeactive n-butcne. The bottoms is mostly ETBE. The distillate is 

Two alternative control structures are evaluated. They differ only in which fresh feed-stream is selected to set the production rate. In the first, the C4 stream is flow controlled. In the second, the ethanol feedstream is flow controlled. 

---

Recent developments and concern over the control of fuel exhaust emissions have led to the increased use of combustion system detergents, oxygenates and cetane improvers in fuel. Oxygenated blend components such as ethanol, methyl t-butyl ether (MTBE), ethyl t-butyl ether (ETBE), and /-amylmethyl ether (TAME) are also used to help limit the exhaust emissions from fuel. 

There has been no field or epidemiological study of populations exposed to ETBE. This is in contrast to MTBE, which has seen a longer and more wide-spread usage. The health effects of MTBE exposure in small human populations and controlled inhalation chamber experiments with volunteers have been reviewed [5]. While there might be justification for an assumption that the outcome of studies on ETBE would not be very different, caution is always necessary before acceptance of this assiunption a minimum database for comparison is a basic requirement. 

Three well-conducted, controlled exposure studies have investigated the effect of pure MTBE on symptoms and objective measures of irritation and performance amongst healthy subjects, hi addition, there has been one similar study of effects of MTBE in gasoline on subjects that have reported themselves as being particularly sensitive to MTBE. There has also been one study of ETBE. 

NMen A, Lof A, Johanson G (1998c) Controlled ethyl tert-hutyl ether (ETBE) exposure of male volunteers (i) toxicokinetics. Toxicol Sci 46 1-10... 

Sundmacher and Qi (Chapter 5) discuss the role of chemical reaction kinetics on steady-state process behavior. First, they illustrate the importance of reaction kinetics for RD design considering ideal binary reactive mixtures. Then the feasible products of kinetically controlled catalytic distillation processes are analyzed based on residue curve maps. Ideal ternary as well as non-ideal systems are investigated including recent results on reaction systems that exhibit liquid-phase splitting. Recent results on the role of interfadal mass-transfer resistances on the attainable top and bottom products of RD processes are discussed. The third section of this contribution is dedicated to the determination and analysis of chemical reaction rates obtained with heterogeneous catalysts used in RD processes. The use of activity-based rate expressions is recommended for adequate and consistent description of reaction microkinetics. Since particles on the millimeter scale are used as catalysts, internal mass-transport resistances can play an important role in catalytic distillation processes. This is illustrated using the syntheses of the fuel ethers MTBE, TAME, and ETBE as important industrial examples. 

However, consider the case when there is only one product the reaction A + B C. Now the column temperature information is not rich enough to use to balance the stoichiometry. This means that the measurement and control of an internal column composition must be used in this neat operation. An example of this type of system is shown in Figure 9.6. The production of ethyl tcrt-butyl ether (ETBE) from ethanol and isobutene produces a heavy product, which goes out of the bottom of the column. The C4 feed stream contains inert components in addition to isobutene. These inerts go out of the top of the column. The production rate is set by the flow controller on the isobutene feed stream. The ethanol concentration on a suitable tray in the column is maintained by manipulating the ethanol fresh feed. ReboUer heat input controls a tray temperature in the stripping section to maintain ETBE product quality. 

Blending and Additives. In the end, all gasoline components are blended together. At a modern refinery, this is done in a computer-controlled process. Additives are used primarily to boost octane rating. Lead was widely used once but was banned in 1996 in the United States, as well as in many other nations. With the increasing prohibition of methyl-tert-butyl-ether (MTBE) in many U.S. states, use of alternatives such as tertiary amyl methyl ether (TAME) or ethyl tert-butyl ether (ETBE) increased. There are many... 

The design of two real reactive distillation systems was explored. Both the MTBE and ETBE systems are basically ternary systems with inerts. The control of these two systems will be studied in Chapter 15. 

If only one product is produced, the temperature profile does not display enough information to enable the use of inferential control for component inventory control purposes. There is only one product leaving the column, and information can be extracted from a limited region where the concentration of this product becomes large. Industrial examples of this type of system are MTBE, ETBE, and TAME. 

CONTROL OF MTBE AND ETBE REACTIVE DISTILLATION COLUMNS... 

In Chapter 9 we explored the steady-state designs of both the MTBE and the ETBE reactive distillation columns using Aspen Plus. In this chapter we export the files into Aspen Dynamics as pressure-driven dynamic simulations and then look at dynamics and control. The control structures evaluated on both systems are based on those developed in Chapter 12 for ternary systems with inerts. 

The temperarnre controller holds stage 22 at 383 K by manipulating the reboiler heat input. Note that the temperature profile in the ETBE system (Fig. 15.15) is much sharper than in the MTBE system (Fig. 15.3). Therefore, a larger temperature transmitter span was used. 

Figure 15.16 Control structure for ETBE with flow control of C4 stream.

---