Zeolites with additives of Nickel helped to purify ethylene from acetylene

Chemists
learned
clean
ethylene
from acetylene
using
zeolite material, doped
Nickel. Due to the ability of Nickel to form complexes with acetylene so it can be cheap and easy to obtain
ethylene of very high purity (impurity
acetylene is less than one ppm).
Results
research published
in the journal Science.

Every year
using
the steam cracking process
get
more
350 million tons of various low molecular
alkenes
— hydrocarbons with a double bond.
Synthesized
in this way alkenes usually
dirty
relevant
alkanes
and alkynes. For example,
ethylene (C2H4)
maybe
contain a small
impurities
ethane (C2H6)
and
acetylene (C2H2). The reaction
able alkyne (hydrocarbons
with a triple bond) — especially undesirable impurity: for example,
if
from
ethylene
in the future get polyethylene,
impurity
acetylene
maybe
not only be embedded in polymer
chain, but also to react with
the catalyst, reducing
its effectiveness.

Usually
for the purification of alkenes
from
alkynes use
selective
partial
hydrogenation on palladium catalyst

very
dear
and
energy
process
Among
alternative routes —
the use of metal-organic frame structures,
materials
which, thanks to
its
the fixed size of the pores can
selectively
to absorb
alcini. However,
due
high costs and inadequate
the stability of metal-organic
frames, this
method yet
not used in industry.

UCO Tea (Chai Yuchao) of Nankai University Xue and Han (Han Xue) from
University
Manchester, along with colleagues suggested
to share
mix
alkenes
and alkynes with
using zeolites—
porous
aluminosilicate
materials.
Zeolites
at
properties similar to
metal-organic
frames (for example, the pores in them are also have
a fixed size), but much cheaper and easier to
receipt. Zeolites
already successfully applied for the separation
various
liquid and gaseous mixtures, but that effectively
to share
alkyne and alkenes with their help, anyone
not
could. Case
that
division
mainly occurs due to the difference
the size and volatility of the molecules,
and these parameters in acetylene and ethylene
enough
close.

Below
to improve the separation selectivity, the authors
the work was placed in the pores of the zeolite
metals that can form
metastable
complexes
with acetylene — zinc
Nickel
and copper.
In
as a basis they chose zeolite
material faujasite
(FAU),
which
synthesized by hydrothermal method
from the aluminate
sodium NaAlO2,
hydrated
silicon dioxide
SiO2,
and
complexes
operauser metal
actually
it
substituted faujasite
part
of sodium ions.
For
that metal was on the inside
surface pores,
used coordinating
ligand
TAPTS.
When
subsequent heating
material
to
544
degrees Celsius
TAPTS
evaporates
and the metal inside the pores forms a connection with
oxygen. Structure
received
materials
was installed
by x-ray
diffraction and
neutron
powder diffraction,
and with the help of x-ray
photoelectron spectroscopy authors
confirmed
that zinc,
copper and Nickel
have
the degree of oxidation
plus
two.

All
three
material
demonstrated good
ability
to absorb acetylene: [email protected],
[email protected] and [email protected]
0,91, respectively, of 1.26 and 1.72 millimol
acetylene per gram.
Absorption
the ability of [email protected]
was not
worse
than that of the metal-organic frameworks —
the most effective of them
the same conditions absorbed
1.7 millimol
acetylene
per gram.
In addition
also, [email protected]
showed
good selectivity: its absorption
capacity in relation to ethylene was
is much lower, at only 0.51 millimol/gram,
due to
lower heat of adsorption of this
connection (25,8
vs. 48.6 kilojoule/mol
for acetylene). Therefore, in the case
passing the mixture of ethylene and acetylene
using [email protected] can be expected that
material
will mainly be adsorbed
acetylene. In addition,
method
temperature-programmed
desorption
shows
during a long transmission mix
gases previously absorbed ethylene is
to decarbonate
from the pores and gradually replaced by
for acetylene.

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