Isomerization of butenes

Similar to IFP s Dimersol process, the Alphabutol process uses a Ziegler-Natta type soluble catalyst based on a titanium complex, with triethyl aluminum as a co-catalyst. This soluble catalyst system avoids the isomerization of 1-butene to 2-butene and thus eliminates the need for removing the isomers from the 1-butene. The process is composed of four sections reaction, co-catalyst injection, catalyst removal, and distillation. Reaction takes place at 50—55°C and 2.4—2.8 MPa (350—400 psig) for 5—6 h. The catalyst is continuously fed to the reactor ethylene conversion is about 80—85% per pass with a selectivity to 1-butene of 93%. The catalyst is removed by vaporizing Hquid withdrawn from the reactor in two steps classical exchanger and thin-film evaporator. The purity of the butene produced with this technology is 99.90%. IFP has Hcensed this technology in areas where there is no local supply of 1-butene from other sources, such as Saudi Arabia and the Far East. 

The effect of butene isomer distribution on alkylate composition produced with HF catalyst (21) is shown in Table 1. The alkylate product octane is highest for 2-butene feedstock and lowest for 1-butene isobutylene is intermediate. The fact that the major product from 1-butene is trimethylpentane and not the expected primary product dimethylhexane indicates that significant isomerization of 1-butene has occurred before alkylation. 

The H2SO4 catalyst produces a high octane product of similar composition from either 2-butene or 1-butene. This fact suggests that the isomerization of 1-butene to 2-butene is more complete than in the HF system. Isobutylene produces a slightly lower product octane than do the / -butenes. The location of a methyl tert-huty ether [1634-04-4] (MTBE) process upstream of the H2SO4 alkylation unit has a favorable effect on performance because isobutylene is selectively removed from the alkylation feed. 

In the Institut Fransais du Petrc le process (62), ethylene is dimerized into polymer-grade 1-butene (99.5% purity) suitable for the manufacture of linear low density polyethylene. It uses a homogeneous catalyst system that eliminates some of the drawbacks of heterogeneous catalysts. It also inhibits the isomerization of 1-butene to 2-butene, thus eliminating the need for superfractionation of the product (63,64). The process also uses low operating temperatures, 50—60°C, and pressures (65). 

The isomerization of 1-butene to cis- and trans- 2-butene onPd/C/Nafion and Pd-Ru/Nafion electrodes is one of the most remarkable and astonishing electrochemical promotion studies which has appeared in the literature.39,40 Smotkin and coworkers39,40 were investigating the electrocatalytic reduction of 1-butene to butane on high surface area Pd/C and Pd-Ru cathodes deposited on Nafion 117 when, to their great surprise, they observed at slightly negative overpotentials (Fig. 9.31) the massive production of 1-butene isomerization, rather than reduction, products, i.e. cis- and trans-2-butenes. This is extremely important as it shows that electrochemical promotion can be used also to enhance nonredox catalytic reactions such as isomerization processes. 

Another difference between the two mechanisms is that the former involves 1,2 and the latter 1,3 shifts. The isomerization of 1-butene by rhodium(I) is an example of a reaction that takes place by the metal hydride mechanism, while an example of the TT-allyl complex mechanism is found in the Fe3(CO)i2 catalyzed isomerization of 3-ethyl-l-pentene. " A palladium acetate or palladium complex catalyst was used to convert alkynones RCOCSCCH2CH2R to 2,4-alkadien-l-ones RCOCH= CHCH = CHCHR. ... 

Isomerizations are another category of reaction where Co complexes act as catalysts. Mixed S,P donor complexes Co(SCN)2(PR3)2 catalyze the isomerization of 1-butene to 2-butene in the presence of NaBH4, with CoH(SCN)(PR3)2 proposed as the active species.1366 A cyclopentadienyl complex (272) is active in the isomerization of quadricyclene to norbornadiene. 

A convincing example of selectivity control in isomerization reactions is the formation of cis-2-butene from the isomerization of 1-butene using the catalyst [(C6H5)3P]2NiX2-P(CeH5)3-Zn-SnCl2 a ratio of c/i-2-bu-tene /ra .s-2-butene as high as 98 2 has been observed. Isomerization to the thermodynamically more stable /ra ns-olefin occurs only after conversion of all the 1-butene (98). Further examples of selective olefin isomerization will be discussed in Section IV,D. 

Worked Example 4.15 The isomerization of 1-butene (X) to form frans-2-butene (XI). The equilibrium constants of reaction are given below. Determine the enthalpy of reaction AH using a suitable graphical method. 

Figure 4.8 The equilibrium constant K for the isomerization of 1-butene depends on the temperature van t Hoff isochore plot of In K (as y) against 1 7 (as x) from which a value of A//°...

All the catalysts (ca.0.6 g) were progressively dehydrated and activated at temperatures 573-673 K and at a final pressure of 2.10 Torr. The adsorption for all the reactants was made at room temperature. The mixed tin-antimony oxide samples were rapidly cooled down to 77 K in order to avoid isomerization of 1-butene following adsorption. 

As an illustration, the isomerization of 1-butene adsorbed on NaGeX or mixed tin-antimony oxides has been carried out. In the methanol to hydrocarbon conversion on the shape selective H-ZSM-5 zeolite, the surface methylation could be observed, the role of... 

A high cisjtrans ratio of 4.4 was observed by Haag and Pines (95) in the isomerization of 1-butene over the same pure alumina (P) catalyst. Although the close agreement of the ratio in dehydration and isomerization may be coincidental, it was suggested that both reactions proceed through the same intermediate. 

To calculate L values using Table I we need forward reaction rates, the number of molecules converted per unit area per second. These reaction rates are most easily obtained at low conversions. But frequently—often for practical purposes—high conversions are reported. We have developed a method for the determination of site densities in a certain class of systems even though the conversion and back reaction are both large. Also, the method can be used under certain conditions even if product isomerization is involved. We shall describe the theory here and in Section III,B apply it to the isomerization of 1-butene to cis- and trans-2-butene over silica-alumina. Although in this article we do not use this method to analyze any other systems, we present it in some detail because it may have potential for further use. 

Lee, S.-H., Shin, C.-H., and Hong, S.B. (2004) Investigations into the origin of the remarkable catalytic performance of aged H-ferrierite for the skeletal isomerization of 1 -butene. J. Catal.,... 

The [Os3(CO)io( t-H)( t-OSi)]surface catalyzes the isomerization and hydrogenation of olefins. When the hydrogenation of ethylene is carried out at 90 °C the trinuclear framework of the initial cluster remains intact in all the proposed elementary steps of the catalytic cycle [133]. However, at higher reaction temperatures the stability of the [Os3(CO)io( t-H)( t-OSi)]sujface depends on the nature of the reactant molecule. It is moderately active in the isomerization of 1-butene at 115 °C but decomposes under reaction conditions to form surface oxidized osmium species that have a higher activity [134]. 

Alkaline earth metal oxides are active catalysts for double bond isomerization. For example, SrO exhibits high activity and selectivity for the isomerization of a-pinene to /1-pinene 110). MgO and CaO have excellent activities for isomerization of 1-butene and 1,4-pentadiene and, particularly, for isomerization of compounds containing heteroatoms, such as allylamine or 2-propenyl ethers 111-115). Recently... 

Froment and BischofT (19) report a study of the dehydrogenation of 1-butene to butadiene on a chromia-alumina catalyst. Neglecting isomerization of 1-butene, the following steps are postulated ... 

Another point illustrated by Table XXIII is the need to carefully consider the effect of lumping isomers for convenience, when mechanistic models are generated. Thus, in Example 4, isomerization of 1-butene is neglected in selecting the elementary steps for butadiene production. In effect, it is assumed that all intermediates are indistinguishable whether 1-butene or a mixture of n-butenes reacts. If that scheme were used in the present case, we could consider a model in which only s, s2, s3, s4, s6, and s j 3 were retained, which would correspond to only a single direct mechanism. However, if instead we chose to retain all the elementary steps as possibilities except Sj j and s12, we would obtain five direct mechanisms for a system producing only 1-butene (in which p — a = 0). 

Only a few attempts have been made to relate the catalytic activity to the properties of cations on the transition metal-exchanged zeolites. Cross, Kemball, and Leach (5) studied the isomerization of 1-butenes over a series of the ion-exchanged X zeolites. Their results with CeX zeolite and the majority of other zeolites indicated a carbonium ion mechanism however a radical mechanism was operative with NiX and in some cases with ZnX. 

Smectite-type materials containing transition metal divalent cations (Ni2+, Co2, and Zn2+) in octahedral sheets were synthesized. The synthetic smectites were thermally stable and had large surface areas and high pore volumes after evacuation at 873 K. Catalytic activities of synthetic smectites were investigated. The Ni2 -containing smectites were active for the isomerization of 1-butene and the oligomerization of ethylene. The Co2+-containing smectites were active for the hydrodesulfurization of thiophene. 

Figure 3 shows the initial activities of the isomerization of 1 -butene. The activities were evaluated from the formation of main products of /wwr-2-butene and cis-2-butene. The activities increased with increasing evacuation temperature and showed a maximum after pre-evacuation at 773- 873 K then the activity decreased to almost zero at 973 K. The selectivities of cis-2-butene/ trarw-2-butene on the Ni-481 and Ni-359 catalysts were found to be 0.6 and 0.7, respectively, meaning that the active sites should be solid acid sites[8]. Figure 4 shows the conversion of ethylene oligomerization on the Ni-481 catalysts. The conversions were evaluated from the formation of the main products of butene and hexene at 120 min. The conversion increased with increasing evacuation temperature and showed a maximum after pre-evacuation at 773- 873 K then decreased to almost zero at 973 K. 

The modification of mesoporous silicate FSM-16 by metal ion-exchange and sulfiding with hydrogen sulfide was studied through the isomerization of 1-butene, cis-2-butene and cyclopropane. It was revealed that the catalytic activities of MeFSM-16 were remarkably enhanced by sulfiding with hydrogen sulfide due to the formation of new Bronsted acid sites... 

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