Chemical Engineering August 2014 - 33

Extracting 1,3-Butadiene
from a C4 Stream
By Intratec Solutions
T
he organic compound 1,3-butadiene
is a petrochemical commodity used as
a raw material for the production of
rubbers and plastics, such as polybutadiene
rubber (PR), styrene butadiene rubber (SBR),
and acrylonitrile butadiene styrene (ABS).
These materials are mainly applied in the
manufacture of automotive parts, tires and
cables. Also, 1,3-butadiene is used as an
intermediate in the manufacture of several
chemicals, such as adiponitrile, the raw
material for nylon production.
1,3-Butadiene is generally recovered from
C4 streams that are generated as byproducts
of ethylene manufacture by naphthabased
steam cracking. These C4 mixtures
are composed mostly of butadiene and
butenes, with smaller amounts of butanes
and acetylenes. To obtain the 1,3-butadiene
product stream, it must be extracted from the
C4 mixture. This can be accomplished using
several technologies, such as separation by
solvent extraction.
The process
The process depicted in Figure 1 is similar
to BASF's (Ludwigshafen, Germany; www.
basf.com) process for butadiene extraction
using aqueous N-methylpyrrolidinone
(NMP) as a solvent.
Extractive distillation. The C4 mixture
containing butadiene, butenes, butanes
and acetylenes is fed to the first extractive
column, where recycled NMP solvent
is added to the top section. The column
overhead stream, which consists of butanes
and butenes (raffinate-1), is sent to storage.
The bottom stream, containing butadiene,
acetylenes and some butenes absorbed in
NMP, is fed to the top of the rectifier column.
In this column, remaining butenes are
separated in the top stream and recycled
to the first extractive column, while the
bottoms stream, containing mainly NMP,
is sent to the degassing section. Butadiene
and some acetylenes are separated as a
Raffinate-1
CW
4
1
C4
mixture
2
ST
CW
FigurE 1. This 1,3-butadiene extraction process is similar to BASF's NMP process
CW
3
ST
ST
Heavy
ends
6
8
7
ST
CW Cooling water
ST Steam
9
CW
Acetylenes
5
FigurE 2.
BASF's NMP process
plants around
the world. Each
mark in the map
corresponds to an
existing facility
side stream of the rectifier column, which
is fed to the second extractive column.
There, recycled NMP solvent is added to
the top to absorb the acetylenes, which
are recovered in the bottoms and returned
to the rectifier column. Crude butadiene is
recovered in the overheads and sent to the
butadiene-purification section.
Butadiene purification. In this section, the
crude butadiene stream is fed to the propyne
column, where propyne is separated
in the overheads. The bottoms stream of
this column is sent to the butadiene distillation
column, where 1,3-butadiene product
is obtained in the overhead stream and
heavy ends are separated in the bottoms.
Degassing. The NMP solvent from the
bottoms of the rectifier column is stripped
from the heavy hydrocarbons, which are
separated as the distillate stream of the
degassing column. These heavy hydrocarbons
are then sent to a cooling column,
where they are cooled by direct contact
with NMP solvent and fed to the rectifier
column through a gas compressor. In the
degassing column, the acetylenes are
separated as a side stream and washed in
a scrubber before being purged. The NMP
recovered in the bottom stream is recycled
to the extractive distillation columns.
Propyne
CW
1,3-Butadiene product
CW
Economic performance
An economic evaluation of the process
was conducted, taking into consideration
a unit processing a C4 stream to produce
100,000 ton/yr of 1,3-butadiene
erected on the U.S. Gulf Coast (the process
equipment is represented in the simplified
flowsheet below). The estimated total fixed
investment for the construction of this plant is
about $50 million.
An important feature of the presented
technology is its low susceptibility to impurities,
rendering it adequate to process any
C4 stream, regardless of the butadiene
content. Also, plants using this technology
have been shown to operate continuously
for more than four years.
In addition, the BASF NMP process technology
is currently applied in several plants
worldwide, as shown in Figure 2. n
Editor's Note: The content for this column is
supplied by Intratec Solutions LLC (Houston; www.
intratec.us) and edited by Chemical Engineering.
The analyses and models presented herein are
prepared on the basis of publicly available and
non-confidential information. The information and
analysis are the opinions of Intratec and do not
represent the point of view of any third parties.
More information about the methodology for
preparing this type of analysis can be found,
along with terms of use, at www.intratec.us/che.
1. First extractive column
2. Rectifier column
3. Second extractive
column
4. Propyne column
5. Butadiene distillation
column
6. Gas compressor
7. Cooling column
8. Degassing column
9. Scrubber
http://www.basf.com http://www.intratec.us http://www.intratec.us/che
Chemical Engineering August 2014

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