Page 154 - Chemical and process design handbook

Speight_Part II_B 11/7/01 3:11 PM Page 2.95

BUTADIENE

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Butadiene (1,3-butadiene, boiling point: –4.4 C, density: 0.6211, flash
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point: –85 C) is made by steam cracking and by the dehydrogenation of
butane or the butenes using an iron oxide (Fe O ) catalyst.
2 3
CH CH CH CH → CH =CHCH=CH + 2H
3 2 2 3 2 2 2
CH CH CH=CH → CH =CHCH=CH + H
3 2 2 2 2 2
CH CH=CHCH → CH =CHCH=CH + H
3 3 2 2 2
In the process (Fig. 1), the crude C fraction is extracted with acetone,
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furfural, or other solvents to remove alkanes such as n-butane, iso-butane,
and small amounts of pentanes, leaving only 1- and 2-butenes and iso-
butene. The isobutene is removed by extraction with sulfuric acid because
it oligomerizes more easily.
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The straight-chain 1- and 2-butenes are preheated to 600 C in a furnace,
mixed with steam as a diluent to minimize carbon formation, and passed
through a 5-m-diameter reactor with a bed of iron oxide pellets (or calcium
nickel phosphate) 90 to 120 cm deep (contact time 0.2 second) at 620 to
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750 C. The material is cooled and purified by fractional distillation and
extraction with solvents such as furfural, acetonitrile, dimethylformamide
(DMF), and N-methylpyrollidone (NMP) (Fig. 2).
Extractive distillation (Fig. 3) is used where the C compounds other
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than butadiene are distilled while the butadiene is complexed with the sol-
vent. The solvent and butadiene pass from the bottom of the column and
are then separated by distillation.
Butadiene is a colorless, odorless, flammable gas, with a boiling point
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of –4.7 C and is used for the manufacture of polybutadiene, nitrile rubber,
chloroprene, and various other polymers. An important synthetic elas-
tomer is styrene-butadiene rubber (SBR) in the automobile tire industry.
Specialty elastomers are polychloroprene and nitrile rubber, and an impor-
tant plastic is acrylonitrile/butadiene/styrene (ABS) terpolymer. Butadiene
is made into adiponitrile, which is converted into hexamethylenediamine
(HMDA), one of the monomers for nylon.

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