MTBE Synthesis

Production of maleic anhydride by oxidation of / -butane represents one of butane s largest markets. Butane and LPG are also used as feedstocks for ethylene production by thermal cracking. A relatively new use for butane of growing importance is isomerization to isobutane, followed by dehydrogenation to isobutylene for use in MTBE synthesis. Smaller chemical uses include production of acetic acid and by-products. Methyl ethyl ketone (MEK) is the principal by-product, though small amounts of formic, propionic, and butyric acid are also produced. / -Butane is also used as a solvent in Hquid—Hquid extraction of heavy oils in a deasphalting process. 

Acid catalysis by titanium silicate molecular sieves another area characterized by recent major progress. Whereas only two categories of acid-catalyzed reactions (the Beckmann rearrangement and MTBE synthesis) were included in the review by Notari in 1996 (33), the list has grown significantly since then. In view of the presence of weak Lewis acid sites on the surfaces of these catalysts, they can be used for reactions that require such weak acidity. 

B. MTBE Synthesis on Zeolite H-Beta Under CF Conditions... 

By characterizing various zeolite catalysts under the same reaction conditions, the authors found weaker MAS NMR signals of alkoxy species for the less active zeolites HY and HZSM-5 than for the more active zeolite H-beta (250). This observation suggests that the alkoxy species observed under steady-state conditions act as reactive surface species in the MTBE synthesis from isobutylene and methanol on acidic zeolite catalysts. 

Table XVII is a comparison of the catalytic activities for liquid-phase MTBE synthesis from isobutylene and methanol (179). The catalyst structure and composition have a strong effect on the activity. The highest activity per proton was obtained with a Dawson-type heteropolyacid, H6P2W 8062, although the acid strength of H WigO is lower than that of the Keggin-type H3PW12O40 (Section HI). Water added to the mixture has little effect on the reaction rate at water concentrations less that 2 wt%, but at 5 wt% the rate is less by a factor of 2.5. At the same time the selectivity is less due to the formation of (erf-butyl alcohol.

The skeletal isomerization of straight-chain paraffins is important for the enhancement of the octane numbers of light petroleum fractions. The isomerization of H-butane to isobutane has attracted much attention because isobutane is a feedstock for alkylation with olefins and MTBE synthesis. It is widely believed that the low-temperature transformation of n-alkanes can be catalyzed only by superacidic sites, and this reaction has often been used to test for the presence of these sites. 

Niiyama et al. (223) found that the reaction rate characterizing MTBE synthesis from methanol and tert-butyl alcohol catalyzed by HjPW 204o increases in proportion to the amount of methanol absorbed in the bulk of HjPW12O40. 

However, Pdi,5PWi204o is active for esterification and MTBE synthesis even in the absence of H2 (378). Therefore, it is concluded that this catalyst is not as simple as Ag3PWi2O40. The catalytic activity of PdrH3 tPW,2O40/SiO2 for hexane isomerization is plotted as a function of x in Fig. 67. The addition of a... 

The synthesis of methyl /-butyl ether (MTBE) from isobutylene and methanol on TS-1 has been investigated. This reaction is catalyzed by acids and the industrial production is carried out with sulfonic acid resin catalysts. It has been reported that at 363-383 K the reaction proceeds in the presence of the acidic HZSM-5, but also on TS-1, which is much more weakly acidic. However, the characterization of the catalysts used is not completely satisfactory for instance, the IR spectra reported do not show the 960-cm 1 band that is always present in titanium-containing silicas. It is therefore possible that the materials with which the reaction has been studied are not pufe-phase TS-1. The catalytic activity for MTBE synthesis is, in any case, an interesting result, and further investigations with fully characterized catalysts are expected to provide a satisfactory interpretation of these results (Chang et al., 1992). 

Methyl fert-butyl ether (MTBE) synthesis 69,70 SMBCR... 

Figure 7 MTBE synthesis conventional scheme (above) and reactive distillation scheme (below).

MTBE synthesis was investigated both theoretically and experimentally. Here, some results for a pilot-scale RD column at Neste Oy Engineering, Finland, are... 

Sundmacher K, Hoffmann U. Macrokinetic analysis of MTBE synthesis in chemical potentials. Chem Eng Sci 1994 49 3077-3089. 

Fig. 4.6. Potential singular point surface and chemical equilibrium surface for MTBE synthesis at 8.11 X 105 Pa.

Fig. 4.7. Reactive reboiler. Intersections of potential singular point surface with reaction kinetic surfaces at four different Damkohler numbers Da, MTBE synthesis at 8.11 x 105 Pa.

Z. Y. Zhang, K. Hidajat, A. K. Ray, Multiobjective optimization of simulated countercurrent moving bed chromatographic reactor (SCMCR) for MTBE synthesis. 

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. 

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 hydrogenation of carbon dioxide was studied using composite catalysts comprised of Fe-Zn-M (M= Cr, Al, Ga, Zr) catalysts and the HY zeolite, where the methanol synthesis and the methanol-to-gasoline(MTG) reaction are combined. The results show that light olefins are important intermediates for iso-butane formation. In all of the cases, the selectivity of isobutane, which can be used as a reactant in subsequent methyl-tert-butyl ether (MTBE) synthesis, was the highest in hydrocarbons. 

Fig. 28 MTBE-synthesis—optimized process with integrated pervaporation. (View this art in Pervaporatior color at www.dekker.com.)...

An unusual feature of the CD process for MTBE production is that it is recovered from the bottom of the CD column even though its normal boiling point (55°C) is less than the boiling point of methanol (64.5°C). This observation is attributed to the formation of a minimum boiling azeotrope from methanol and MTBE. Apparently, if sufficient quantities of MTBE were accumulated in the CD column, it would lift the methanol into the reaction zone of the column resulting in a higher methanol conversion. This unusual behavior is believed to be responsible for the multiple steady states observed in the MTBE synthesis shown in process simulation and optimization studies and verified experimentally. ... 

A large number of papers have been published on the process modeling and optimization of the etherification process. More details could be found in a handbook. The most important aspect of process improvement is catalyst improvement because the Amberlyst ion-exchange resin used in the MTBE synthesis has an upper thermal stability limit of less than 100°C and there is a need to develop other acidic catalysts with higher thermal stability. Some of the recent papers have described the use of zeolites. 

The conventional MTBE synthesis consists of a reaction of isobutene and methanol over an acidic sulfonated cation-exchange catalyst. This reaction is highly selective, equilibrium-limited, and exothermic in nature. Several types of industrial reactors such as tubular reactors, adiabatic reactors with recycle, and catalytic distillation configurations have been utilized to cany out the MTBE synthesis reaction. The factors considered in the optimal design of a MTBE unit include the following items [52]. 

Higher levels of conversions (> 99%) can be achieved by a two-stage MTBE synthesis process (Figure 3.26). The first reactor is a typical MTBE synthesis, using isobutene and methanol as feeds over a packed-bed ion-exchange reactor. The product is separated in a debutanizer tower and the overhead of this reactor is charged to another synthesis reactor to achieve higher conversion of isobutene. A secondary debutanizer is used to separate the additional MTBE produced in the secondary packed bed reactor. Methanol removed from the overhead stream is recycled back to the primary synthesis reactor [52]. 

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]. 

---