Synthesis of MTBE

The fuel ether MTBE is synthesized by the liquid-phase reaction of isobutene (IB) and methanol (MeOH) using macroreticular sulfonic acid ion-exchange resins as catalysts. The stoichiometric equation is given by 

The microkinetics of this reaction were investigated in detail by Rehfinger and Hoffmann [7]. These authors proposed the following rate expression in terms of liquid-phase activities the derivation is described in Section 5.4.3 

r stands for the volumetric reaction rate, Ci represents the concentration of acid groups per unit volume of catalyst, and a, is the liquid-phase activity of component i. The temperature dependence of the reaction rate constant k can be expressed by the Arrhenius equation. All kinetic and thermodynamic parameters can be found elsewhere [7]. 

By increasing the Damkohler number, the influence of the chemical reaction is fortified. For Da = 10 (Fig. 5.16b) the shape of trajectories starting with a relatively high mole fraction of MeOH is still similar to those of distillation without reaction, so that pure MeOH remains a stable node in the system. Near the MTBE vertex, the conditions change remarkably. The reaction vector is pointed towards the chemical equilibrium line (dashed curve). As a consequence, the stable node moves from 

Further enhancement of Damkohler number to Da = 2 X 10 (Fig. 5.16c) leads to the situation in which the lower stable node coincides with the saddle point so that they extinguish each other. Hence the trajectories run into pure MeOH. At Da = 1 (Fig. 5.16d) the reaction vector is dominant in relation to the separation vector. Thus every residue curve is dominated by the stiochiometric restriction when moving towards the curve of chemical equilibrium. Because of the dominance of chemical reaction, the trajectories do not pass this line, but remain on it until they reach the pure MeOH vertex. 

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Typical feedstock composition and product properties for the synthesis of MTBE-ETBE. 

Synthesis of MIBK Synthesis of MTBE Removal of O2 from water ... 

Clay-supported heteropoly acids such as H3PW12O40 are more active and selective heterogeneous catalysts for the synthesis of MTBE from methanol and tert-butanol, etherification of phenethyl alcohols with alkanols, and alkylation of hydroquinone with MTBE and tert-butanoi (Yadav and Kirthivasan, 1995 Yadav and Bokade, 1996 Yadav and Doshi, 2000), and synthesis of bisphenol-A (Yadav and Kirthivasan, 1997). 

MTBE is used on a large scale as an octane number boosting additive in unleaded gasoline. Sulfonic acid resins are applied as efficient catalysts for the industrial production of MTBE from methanol and isobutylene (222). Since 1987, investigations of the synthesis of MTBE with reactants in the gas phase have been performed with zeolites HY (223-225), H-Beta (226), HZSM-5 (224,225), and H-BZSM-5 (227) as catalysts. 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/... 

Applying the equipment shown in Fig. 13 (Section III.B) the authors performed a simultaneous analysis of the reaction products leaving the MAS NMR rotor reactor by on-line gas chromatography and an NMR characterization of the compounds adsorbed on the catalyst under steady-state conditions. These investigations showed that the intensity of the signals at ca. 80 ppm correlates with the yields of MTBE determined by gas chromatography (60). An increase of the reaction temperature of the exothermic synthesis of MTBE from 333 to 353 K, led to a simultaneous... 

Fig. 24. MAS NMR spectra recorded in the steady state of the synthesis of MTBE by isobutylene and methanol on calcined zeolite H-Beta (nsi/tiAi = 16) (a—c) and after purging of the catalyst with dry nitrogen (d). Reproduced with permission from (230). Copyright 2000 Elsevier Science.

The two-film model representation can serve as a basis for more complicated models used to describe heterogeneously catalyzed RSPs or systems containing suspended solids. In these processes a third solid phase is present, and thus the two-film model is combined with the description of this third phase. This can be done using different levels of model complexity, from quasi-homogeneous description up to the four-film presentations that provide a very detailed description of both vapor/gas/liquid-liquid and solid/liquid interfaces (see, e.g., Refs. 62, 68 and 91). A comparative study of the modeling complexity is given in Ref. 64 for fuel ether synthesis of MTBE and TAME by CD. 

In this work, the triflic acid modified Y-zeolite catalyst has been investigated for the atmospheric synthesis of MTBE and ETBE. In particular, the apparent activation energy for MTBE was determined, and this value is compared with those reported in the literature [1,6]. In addition, for both syntheses, the product selectivities are reported as functions of the contact time at the temperature where the catalyst activity is the highest. The catalyst stability for the MTBE synthesis was also examined. 

The synthesis of MTBE is carried out in the liquid phase over a fixed bed of ion... 

Salomon MA, Coronas J, Menendez M, and Santamarfa J. Synthesis of MTBE in zeolite membrane reactors. Appl Catal A Gen 2000 200 201-210. 

These zirconium phosphate materials are being developed as replacements for ion exchange resin catalysts. The arylsulfonic acid MELS have been evaluated for butene isomerization, methanol dehydration, MTBE synthesis as well as cracking, and for the alkylation of aromatics. In the synthesis of MTBE this catalyst appears to out-perform the ion exchange resins, Amberlyst 15. 

The synthesis of MTBE is carried out in the liquid phase over a fixed bed of ion exchange resin in the form. The rate of reaction of isobutene with methanol is much higher than that of the n-butenes (isobutene forms a relatively stable tertiary carbenium ion in the first step), which enables the selective conversion of isobutene in the presence of the M-butenes. In fact, streams with an isobutene content as low as 5% can be converted. 

Processes based on these catalysts could provide isobutene and isopentene for the synthesis of MTBE (methyl tert-butyl ether) and TAME (tert-amyl methyl... 

The synthesis of MTBE also can be carried out using methanol and n-bu-tenes or mixed butanes, or n-butane as the C4 feed. These feeds are typical of Middle East situations, where there is an abundantly higher supply of LPG as compared to isobutene. Although these substitute C4 feeds are not commercially used for MTBE synthesis, their usage is feasible (Figure 3.27) [52]. 

In 1992, refiners began to choose a variety of routes to the synthesis of MTBE [51]. Valero Refining Marketing, in its MTBE synthesis plant, uses a butane/butylene mixture from the heavy oil cracker vapor recovery unit which on hydrogenation converts butadiene to butylene. This is then mixed with methanol in the MTBE synthesis unit, the MTBE product is separated and the butane/butene stream is charged to the alkylation unit. The butadiene is removed from the alkylation unit. This improves alkylate quality and reduces acid consumption. A block diagram of this unit is shown in Figure 3.29. 

Conventional raw materials in the synthesis of MTBE are methanol and isobutene. However, it is believed that there may not be enough supply of isobutene to meet the increasing MTBE demand. One of these alternatives is... 

The acid catalysis of MTBE plays an important role in many different areas of application. The key aspect is the synthesis of MTBE using solid acid catalysts since it has become the most important fuel oxygenate in the world. As this reaction is reversible, the cleavage of MTBE is used to gain pure isobutene, a basic chemical required for various products. Furthermore, the hydrolysis of MTBE has been investigated regarding its role in environmental chemistry. Besides its prominence in analysis, the use of this reaction in the treatment of contaminated water is discussed. 

MTBE synthesis from /-butanol and methanol in a membrane reactor has been reported by Salomon et al. [2.453]. Hydrophilic zeolite membranes (mordenite or NaA) were employed to selectively remove water from the reaction atmosphere during the gas-phase synthesis of MTBE. This reaction was carried out over a bed of Amberlyst 15 catalyst packed in the inside of a zeolite tubular membrane. Prior to reaction, the zeolite membranes were characterized by measuring their performance in the separation of the equilibrium mixture containing water, methanol, /-butanol, MTBE, and isobutene. The results obtained with zeolite membrane reactors were compared with those of a fixed-bed reactor (FBR) under the same operating conditions. MTBE yields obtained with the PBMR at 334 K reached 67.6 %, under conditions, where the equilibrium value without product removal (FBR) would be 60.9%. 

The application of the method for the synthesis of MTBE, TAME and other octane improvers for gasoline is proposed. An application of the method to branch alkenes synthesised by a selective Fischer-Tropsch catalyst is demonstrated. 

A particularly favourable application would be in the synthesis of MTBE and TAME. The selective reaction of methanol with the branched alkene would enable the straight chain alkenes to be recycled through the isomerization catalyst. Since the methanol for such a process would likely be synthesised from CO and Hg it would be possible to run this process in parallel with an alkene selective Fischer-Tropsch process to achieve a self contained conversion of CO and to a high octane fuel blend stock. 

Finally, integrating chemical reaction and separation in a single vessel offers opportunities for waste reduction. As an example of this strategy, consider the synthesis of methyl-tert-butyl ether (MTBE). Two processes are in common industrial use in the synthesis of MTBE from methanol and isobutylene. In one process, a series of fixed-bed catalytic reactors send a mix of product, unreacted methanol, and unreacted isobutylene to a series of separation devices. In an alternative process configuration, the feed materials are sent to a distillation column that contains a series of catalytic beds. The processes are contrasted in Fig. 17. There are several advantages to the catalytic distillation configuration ... 

P-ll - Influence of OH groups of Beta zeolites on the synthesis of MTBE... 

Vapor phase synthesis of MTBE over zeolite Beta is very efficient. For example. Beta zeolite is three times more active than Amberlyst-15 for MTBE vapor phase synthesis at 50°C. The better catalytic performance of H-Beta was verified in liquid phase. The external surface area, the amount of bridging AlOHSi, and silanol groups are important zeolite parameters for the ether synthesis. The reaction occurs on bridging AlOHSi acid sites. The highest yields are reached for low SiOH/AlOHSi ratios where methanol clusters bonded to silanol groups allow accessibility of isobutene to the active AlOHSi groups. 

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/ Mg = 80). The catalyst was calcined in a glass insert, which was sealed after the loading with MTBE. H MAS NMR spectra were recorded during the heating period of 100 s. Then the laser power was switched off and the temperature of the samples fell back to room temperature within about 60s. During the stop period of 1 h, when the reaction state was frozen, a C MAS NMR spectrum was recorded. By repetition of the stop-and-go periods for several times, the complete reaction could be measured by both H and MAS NMR spectroscopy. 

Fig. 24. MAS NMR spectra recorded in the steady state of the synthesis of MTBE by isobutylene...

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