Butenes Conversion

Reaction Cycle 2-Butene Conversion, % Selectivity to Saturated Cg, % TMP Selectivity Isoctanes Fraction,... 

Moreover, the catalyst deactivation must also be considered in order to use these solid materials in industrial processes. Figure 13.8 shows the variation of catal54ic activity (2-butene conversion) with the time on stream obtained under the same reaction conditions on different solid-acid catalysts. It can be seen how all the solid-acids catalysts studied generally suffer a relatively rapid catalyst deactivation, although both beta zeolite and nafion-sihca presented the lower catalyst decays. Since the regeneration of beta zeolite is more easy than of nafion, beta zeolite was considered to be an interesting alternative. ... 

The zeolite composition and structure, which can affect hydrogen transfer activity, are important parameters determining the activity, selectivity, and stability of the zeolite during isobutane alkylation. In the case of USY zeolites, a maximum initial 2-butene conversion was observed for a framework Si/Al ratio of about 6 (63). However, the TMP/DMH ratio, which can be taken as a measure of the alkylation/oligomerization ratio, continuously increased when decreasing the framework Si/Al ratio. On the other hand, the amount and nature of extraframework Al (EFAL) species also affected the alkylation properties of USY zeolites (64). 

Fig. 3. Influence of USY zeolite unit cell size on the initial (TOS= 1 min) 2-butene conversion and TMP/DMH ratio during isobutane/2-butene alkylation at 50°C, 2.5 MPa total pressure, i-C4/2-C4 molar ratio of 15, and W1ISV (referred to the olefin) of 1-4 h 1.

This mechanism therefore involves interconversion between trans- and cis-2-butene in accordance with their experimental results. The activation energy for the anti- to syn-Tr-allyl conversion is about 50 kJ moP higher than that for the conversion of cis-2-butene to 1-butene. The forbidding activation energy for cis trans-2-butene conversion therefore effectively eliminates the direct anti- to syn-iT-allyl transformation at lower temperatures. 

Initial 2-butene conversion during ieobutane/bulene alkylation (a) and relative surface acidity (b) of monovalent salts of 12-tungstopho phoric acid (HPW) as a function of cation content per keggin unit. Reproduced with permission from [33]. 

Fig. 9. Change of the initial 2-butene conversion (a) and initial TMP/DMH ratio (b) with the framework A1/(A1 -i- Si) ratio of USY zeolite. Reaction conditions T= 50°C, P = 20 bar, I/0 = 15,WHSV=lh-i.

Fig. 15. Change of 2-butene conversion with TOS for 864 /Zr02 (SZ) and H-beta zeolite during isobutane/2-butene alkylation in a fixed bed reactor at the reaction temperature of 50°C (closed S5mibols, solid lines) and 0°C (open s5mibols, dashed lines), 25 bar total pressure, I/O molar ratio of 15, and olefin WHSV of 1 h Data adapted from Ref (181).

Fig. 21. Initial 2-butene conversion as a function of cation content (x) and evolution of conversion with TOS for the most active catalysts during isobutane/2-butene alkylation over group B salts of HPW. Alkylation conditions fixed bed reactor, 80°C, 2.5 MPa, I/O = 15, olefin WHSV = Ih-i.

Mixed WOj/Al Oj/HY catalysts prepared by calcination of physically mixed WO3, Al Oj and HY zeolite showed unique behavior in the metathesis between ethene and 2-butene to produce propene [147]. Monomeric tetrahedrally coordinated surface tungstate species responsible for the metathesis activity were formed via the interaction with Bronsted acid sites of HY zeolite. Polytungstate clusters are supposed to be less active in the metathesis reaction. The best catalyst demonstrates the 2-butene conversion close to the thermodynamic equilibrium value ( 64%) at 453 K. The catalysts are bifunctional [148] they catalyze first isomerization of 1-butene to 2-butene and then cross-metathesis between 1-butene and 2-butene to produce propene and 2-pentene. 10%W03/Al203-70%HY exhibits the highest propene yield. 

This arrangement ensures more efficient overall catalyst utilization and a significant increase in the yield of octenes. As an example, dimer selectivity in the 90-92 % range with butene conversion in the 80-85 % range can be obtained with a C4 feed containing 60 % butenes. Thanks to the biphasic technique, the dimerization... 

TABLE 6.1. The 1-butene conversion and product distribution after 1 h of alkylation reaction of isobutane on as-prepared JML-I50 and zeobte Beta catalysts. 

The 1-butene conversion and product distribution obtained at 25°C after 1 h of alkylation reaction of isobutane on JML-I50 and Beta catalysts are summarized in Table 6.1. The conversion (97%) with JML-I50 catalyst is higher than that (86%) with zeolite Beta. The primary products with the above catalysts are Cs compounds (59.9% with JML-I50 and 62% with Beta). The Cg products mainly consist of trimethylpentanes (TMPs), 58.7% for JML-I50 and 73% for zeolite Beta. The TMP/DMH (dimethylhexane) ratios are 13.5 for JLM-I50 and 4.1 for Beta, demonstrating that the selectivity of JML-I50 is higher than that of zeolite Beta. The yields of alkylate are 6.6 mL and 5.2 mL for JML-I50 and Beta zeolite, respectively. The weights of alkylate produced per weight of butene fed to the reactor are 1.13 and 0.95 for JML-I50 and zeolite Beta, respectively. 

Rorvik, T., Mostad, H.B., Karlsson, A., and Ellestad, O.H. (1997) Isobutane/ 2-butene alkylation on fresh and regenerated La-EMT-51 compared with H-EMT. The catalysts selectivity changes at high butene conversion in a slurry reactor. Appl. Catal. A, 156, 257-283. 

In sill C MAS NMR spectroscopy has also been applied to characterize the scrambling in n-butene conversion on zeolite H-ferrierite (97), n-butane conversion on SZA (98), -butane isomerization on Cs2,5Ho.5PWi204o (99), n-pentane conversion on SZA (100), isopropylation of benzene by propene on HZSM-11 (101,102), and propane activation on HZSM-5 (103-105) and on Al2O3-promoted SZA (106,107). The existence of carbenium ions was proposed to rationalize the experimental scrambling results observed by in situ MAS NMR spectroscopy. 

Fig. 5. Dependence of butene conversion on temperature and composition of catalyst (Bi/Mo ratio).

Catalyst Temperature (°C) Feed (atm) Order Butene conversion (%) Butadiene selectivity (%) Reference... 

The 2-butanol feedstock is conventionally obtained by the sulfuric acid-catalyzed addition of water to -butenes. This is a two-step reaction involving sulfation and hydrolysis in which the conversion of -butenes is 90% and selectivity to 2-butanol is 95% (15). During operation the sulfuric acid becomes diluted and must be reconcentrated before reuse. In 1983 Deutsche Texaco commercialized a single-step route in which 2-butanol is formed by the hydration of -butenes in the presence of a strongly acidic ion-exchange resin containing sulfonic acid groups (16—18). The direct reaction is carried out at 150—160°C and 7 MPa. Virtually anhydrous 2-butanol is recovered in this process (19). Direct hydration requires lower utilities and investment costs, operates at 99% selectivity to 2-butanol, but is hindered by low (5—15%) -butene conversion per pass. 

The isobutane-1 -butene alkylation was studied in dense CO2 in both fixed-bed and slurry reactors.165-167 Both Nafion SAC-13 and Nation SAC-25 exhibited steady-state conversions and selectivities for 50 h. Enhanced Cg alkylate selectivity could be achieved at near total butene conversion. The maximum value attained, however, was only about 40%. The higher effective alkylation rate constant for SAC-25 compared to SAC-13 indicates improved accessibility of the acid sites. Nafion SAC-13 and SAC-25 applied in a study to test the effect of supercritical fluids on alkylation exhibited only modest activities.168... 

The isopentene was 82 per cent 3-methy 1-1-butene. ) Conversion of the higher olefm reactant. 

For all samples a marked decline of the 1-butene conversion is noted in the first 5 hours in time-on-stream (Fig. la), whereas for longer times-on-stream the activity declines at a much slower rate. The selectivity to MEK also changes considerably in the first 5 hours (Fig. lb). Initially, the selectivity of all samples is very low and significantly increases in the first 1-2 hours up to a maximum and then later declines further to a nearly constant value (activity and selectivity only decrease slightly) after around 5 hours. For the sample prepared from PdS04 (C), only an increase in the selectivity is ob-... 

The comparison of the results of MEK and water adsorption with those of IR characterization (Fig. 3) and of the effect of higher temperature treatment with 02 and N2 (Fig, 1) suggests that initially (clean surface) the supported catalysts are very active, but probably the MEK formed is rapidly consecutively converted to acetate species which remain on the surface together with the MEK formed. The progressive formation of a water layer on the surface as well as the effect of the catalytic reaction itself leads to an in-situ change in the surface reactivity with a decrease in the rate of 1-butene conversion, but an... 

The conversion and selectivity patterns of the catalyst with additional potassium is presented in Fig, 3. The activity of the promoted catalyst shows a rather featureless pattern. After displaying a small initial butene conversion, it decreases to the level of a deactivated catalyst. 

PFAS were obtained with 2 moles of water, for each mole of acid and they could not be dehydrated with physical methods. Hydrated acids, both as such and supported on silica using water as solvent, were not active in isobutane alkylation. Therefore the effect of different dehydrating solvent was studied, in order to remove residual water. The catalysts obtained by supporting perfluoroethanedisulphonic acid on Si02 (PFES-Si02) after dissolution in various dehydrating solvents were tested in the reaction and resulted active with high butene conversion (Table 1). 

Lowering reaction temperature, the selectivity to saturate octanes was highly increased reaching the value of 94%, while butene conversion remains complete. Selectivity to trimethylpentanes reaches very high values (always >85%). 

Figure 9 1-butene conversion versus Purge Gas Flow Rate... 

The example was chosen to illustrate pathway reduction and the resulting simplification of mathematics. So as not to distract from that message, complications encountered in practice with this particular reaction were disregarded. These include isomerization of 2-cis- to 2-tram- and 1-butene, conversion of 1-butene to 2-methyl butanal and n-pentanal, and aldol condensation of the latter (see also Example 11.1 in Section 11.2). 

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