2- Butene products from reducing butadiene

Refining and Isomerization. Whatever chlorination process is used, the cmde product is separated by distillation. In successive steps, residual butadiene is stripped for recycle, impurities boiling between butadiene (—5° C) and 3,4-dichloto-l-butene [760-23-6] (123°C) are separated and discarded, the 3,4 isomer is produced, and 1,4 isomers (140—150°C) are separated from higher boiling by-products. Distillation is typically carried out continuously at reduced pressure in corrosion-resistant columns. Ferrous materials are avoided because of catalytic effects of dissolved metal as well as unacceptable corrosion rates. Nickel is satisfactory as long as the process streams are kept extremely dry. 

Acetonitrile serves to greatly enlarge the spread of relative volatilities so that reasonably sized distillation equipment can be used to separate butadiene from the other components in the C4 fraction. The polar ACN acts as a very heavy component and is separated from the product without much difficulty.The feed stream is carefully hydrogenated to reduce the acetylene level rerun, and then fed to the single stage extractive distillation unit. Feed enters near the middle of the extractive distillation tower, while (lean) aqueous ACN is added near but not at the top. Butenes and butanes go overhead as distillate, with some being refluxed to the tower and the rest water washed for removal of entrained ACN. 

Some of the evidence for such structures comes from the change in product distribution of the butenes as a function of cyanide concentration when butadiene is hydrogenated with pentaeyanocobaltate(II) catalyst or when the a butenyl complex is reduced with the hydride complex [HCo(CN)5] . Thus 1-butene is the major product in the presence of excess CN, and major product in the absence of excess cyanide. The 1-butene presumably arises from the cleavage of a tr complex, and the 2-butene via an intermediate w-allyl complex. The Tr-allyl complexes of cobalt tricarbonyl are well-characterized and can be prepared either from butadiene and HCo(CO)4 or from methallyl halide and NaCo(CO)4 [49). 

The effect of nitric oxide or oxygen on the photolysis of cis- or trflnj-butene-2 was quite striking The yields of ethane, propene, -butane, butene-1, isobutane and Cj to Cg compounds were reduced sharply to levels well below those from corresponding runs with nitrogen. In contrast, allene, methane, ethylene, acetylene, butene-2 and butadiene were affected only to the same extent as the runs with nitrogen. It is concluded that the products in the latter group are primary while those of the former group are secondary and arise from free radicals produced in primary steps. 

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. 

Ni (II) phosphate, VSB-I, develops a unidimensional pore system which is delineated by 24 Ni06 and PO4 polyedra and the free diameter of the chaimel is estimated to be 8.8 A. It becomes microporous on calcination in air at 350°C. For cyclodimerization of 1,3-butadiene, VSB-1 itself shows excellent selectivity for ethylbenzene. Reduced Ni-VSB-1 yields good selectivity for hydrogenation of 1,3-butadiene to butenes and Pd-containing VSB-1 exhibit good catalyst performance for direct production of H2O2 from H2 and O2. 

Exploration of Basic Catalyst Components The study of direct oxidative acetoxyla-tion of 1,3-butadiene began with the use of Wacker-type homogeneous catalyst Pd(OAc)2-CuCl2 [10]. This catalyst system gave low l,4-diacetoxy-2-butene selectivity, and there was a problem in separating the catalyst. After that, liquid-and vapor-phase methods using a Pd-based catalyst were studied in parallel. Catalyst activity was greatly improved by the addition of Bi or Sb to the Pd catalyst in the gas-phase reaction [11]. However, catalyst activity was reduced by the adhesion of resin by-product derived from unsaturated aldehydes on the catalyst surface. Various improvements have been tried in the gas phase, but catalyst robustness has never met industrial requirements. 

A proposed expansion of the company s styrene-butadiene rubber production will require an additional 10,000 tons/yr of butadiene as a raw material. For many years, butadiene has been manufactured by dehydrogenating butene or butane over a catalyst at appropriate combinations of temperature and pressure. It is customary to dilute the butene feed with steam (10 to 20 mol HjO/mol butene) to stabilize the temperature during the endothermic reaction and to help shift the equilibrium conversion in the desired direction by reducing the partial pressures of hydrogen and butadiene. The current processes suffer from two major disadvantages ... 

Dehydrogenation—In general, hydrogenation catalysts can also remove hydrogen from organic compounds. The production of olefins and diolefins fiom paraffins is an important commercial process. Formation of butene from butane is favored at about atmospheric pressures while butadiene is favored at reduced pressures. 

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