Hydrogenation of butadiene to butenes

Mo, W) decreases with the increase in basic strength of the framework oxygen of the host zeolite [32]. The M(CO)3(Oz)3 (Oz = zeolite framework oxygen) species generated by the thermal treatment are active in the stereoselective hydrogenation of butadiene to cis-2-butene [33, 34]. 

Proposed Mechanism for Butadiene Reduction. The above results are compatible with the reaction sequence illustrated below. In the absence of a hydrogen atmosphere, CoH, formed via the aging reaction of cyanocobaltate(II), reacts reversibly with butadiene to yield Co(C4H7) which reacts further with CoH and/ or undergoes hydrolysis to yield butenes. The over-all result is oxidation of cyano-cobaltate(II) to cyanocobaltate(III) with concomitant reduction of butadiene to butenes. 

Examination of the reaction products indicated that the primary products of reaction were probably butadiene and H2S. The rates of hydrogenation of butadiene and butene were found to be consistent with the amounts appearing in the reaction products (provided, in the case of cobalt molybdate catalyst, that H2S was present to simulate reaction conditions). The results support the view that C-S bond cleavage is the first step in thiophene desulfurization, rather than hydrogenation of the ring. 

The existence and formation of butadiene severely reduced the activity of the catalyst. However, in our experiments, the ratio of butadiene to butenes was always less than 0.01. Furthermore, as shown previously, the activity of the catalyst remains constant during the experiments. For these reasons it is assumed that butadiene had no profound effect on the kinetics of the dehydrogenation and hydrogenation. 

The oxygenation of olefines to form epoxides is also possible by means of Mn (salen) anchored in Y-zeolite [66]. Furthermore selective hydrogenations are known using Pd (salen) encapsulated in X- and Y-zeolite [71]. M. Ichikawa and coworkers used a special electron donor acceptor complex (Na )4(FePc )/NaY for the selective hydrogenation of butadien to 2-butene and found that the entrapped complex results in a higher trans/cis ratio of 2-butenes than the complex on the external surface of NaY [70]. 

Table 41.4 Comparison of the hydrogenation of 1,3-butadiene to butenes in different solvents [70].

The heavy lines in Figure 1 indicate reactions which were experimentally shown to occur—the conversion of thiophene to butadiene in one step, followed by hydrogenation of the butadiene to butene, for example. The results do not eliminate the possibility of two hydrogenation steps occurring on one site (see dashed lines in Figure 1). 

CDTECH Isobutylene Raffinate 1 Selective hydrogenation of butadiene and hydroisomerization of butene-1 to butene-2 via catalytic distilation to recover isobutylene 1 1994... 

Tables 3.10, 3.11 and 3.12 provide economic data on techniques for the selective hydrogenation of butadiene contained in a C4 cut, on the processes for the separation and manufacture of isobutene, and on those relative to the production of n-butenes.

The methylvinyl radical (IV) can abstract a hydrogen atom from a feed or product molecule to form propylene or it can lose a hydrogen atom to form allene or propadiene as products. For the 2-butenes, steric factors inhibit methyl radical addition thus C5 products are formed to a far lesser extent than from 1-butene. While ethylene may be formed by a sequential decomposition of propylene, this cannot be the only path for its formation, as the yield of ethylene in the high conversion region increases about twice as rapidly as does the methane yield. An additional source of ethylene is the symmetrical cleavage of butadiene to vinyl radicals. 

The selectivity into butenes, defined by the ratio [butenes] / [butenes + butane] is controlled by two parameters. One is kinetic and measures the butene hydrogenation rate relative to the butene desorption rate. The other one is thermodynamic and depends on the relative adsorption coefficients of butadiene and butenes. It will fix the relative coverages in butadiene and butenes on the surface as a function of their relative pressures. In practice the second parameter, the thermodynamical one, turns out to be preponderant and then fixes the selectivity into butenes as a function of the conversion percentage. A better selectivity will be observed if butadiene is more strongly adsorbed than butene, or in other words, if the ratio between adsorption coefficients bdiene/bbutenes is high. 

Table 3 Catalytic activity for the first reaction (butadiene to butenes) on (111) and (110) faces of Pd, Pt and Ni (at 293 K, 10 torr H2 and an hydrogen/hydrocarbon ratio of 5-10 [29, 33 ]. ...

The selectivity of metal catalysts improves in some reactions with alloying for example the alumina-supported Pd-Cu catalyst hydrogenales butadiene to 1-butene with 99% selectivity, i.e. the isomerization is less than lOli. The explanation is that hydrogen adsorption decreased on the Cu-containing catalysts . Similarly, better selectivities were observed with a polymer anchored Pd, or a Pd-Co catalyst in the gas-phase hydrogenation of butadiene and cyclopentadiene in a hollow-liber reactor 2 in the liquid-phase hydrogenation of 1,5-hexadiene with Pd-Ag catalyst. ... 

Not only metals but some oxide catalysts are active in diene hydrogenation ZnO modified by Sn(CH3)4 afforded 1-butene in hydrogenation of butadiene at room temperature. Reduced and sulfided moUbdena on alumina catalyst hydrogenated butadiene and cyclohexadiene selectively5 . When the transition metal complex Mo(CO)6 was encapsulated in NaY zeolite cages, it converted //wnv-l, 3-pcnladicnc to cA-2-pentene and 1,4-pentadiene to c -l,3-pentadiene at 150°C °. Cr(CO)3 encaged in LiX or NaX zeolite was efficient and selective in butadiene hydrogenation to cw-2-butene . ... 

Haruta and co-workers [437] have investigated the selective hydrogenation of 1,3-butadiene to butenes over AU/AI2O3, Au/Si02 and Au/Ti02 prepared by DP, GG and LG methods. All the Au catalysts were 100% selective to butenes, with 65-75% of selectivity to 1-butene. They found that the reaction was almost insensitive to the size of the Au particles (2.5-7 nm) and to the nature of the oxide support. 

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. 

The butanediol synthesis process developed by Mitsubishi in Japan comprises three steps acetoxyiation of butadiene to 1.4-diacetoxy 2-butenes, the hydrogenation of this compound to 1,4 diacctoxybutane. and, finally, hydrolysis to 1,4-butanedioL... 

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