Investigation of the selective production of ethylene from propylene over small-pore zeolites

Article abstract of DOI:10.1166/jnn.2019.15993

The selective production of ethylene from the direct conversion of propylene (propylene-to-ethylene, PTE) was examined for the first time using various types of 8-membered ring (8-MR) zeolite materials with different pore structures. Among these 8-MR zeolites, SSZ-13 zeolite with a threedimensional chabazite structure exhibited the highest ethylene yield. To increase the ethylene selectivity further, the PTE reactions were conducted over SSZ-13 zeolite external surface modifications with silylation or phosphorus. The external surface modifications enhanced the ethylene selectivity due to the passivation of external acid sites. The surface-modified SSZ-13 catalyst exhibited the highest selectivity to ethylene, at more than 90% at 450 °C, a WHSV of 0.33 h^-1, and a propylene particle pressure of 0.1 MPa.

Full text of DOI:10.1166/jnn.2019.15993

Article
Journal of
Nanoscience and Nanotechnology
Vol. 19, 2183–2188, 2019
Copyright © 2019 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Investigation of the Selective Production of Ethylene from
Propylene Over Small-Pore Zeolites
1
1ꢀ2ꢀ∗
, and Chul-Ung Kim1ꢀ2
Jong-Won Jun , Tae-Wan Kim
1Center for Convergent Chemical Process, Korea Research Institute of Chemical Technology,
41 Gjeong-ro, Yuseong, Daejeon 34114, Republic of Korea
Department of Advanced Materials and Chemical Engineering, University of Science and Technology (UST),
17 Gajeong-Ro, Daejeon 34114, Yuseong, Republic of Korea
1
2
2
The selective production of ethylene from the direct conversion of propylene (propylene-to-ethylene,
PTE) was examined for the first time using various types of 8-membered ring (8-MR) zeolite
materials with different pore structures. Among these 8-MR zeolites, SSZ-13 zeolite with a three-
dimensional chabazite structure exhibited the highest ethylene yield. To increase the ethylene selec-
tivity further, the PTE reactions were conducted over SSZ-13 zeolite external surface modifications
with silylation or phosphorus. The external surface modifications enhanced the ethylene selectivity
due to the passivation of external acid sites. The surface-modified SSZ-13 catalyst exhibited the
ꢀ
−1
highest selectivity to ethylene, at more than 90% at 450 C, a WHSV of 0.33 h , and a propylene
particle pressure of 0.1 MPa.
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
Keywords: Propylene-to-Ethylene, Olefin Interconversion, Surface-Modified SSZ-13.
Copyright: American Scientific Publishers
Delivered by Ingenta
1
. INTRODUCTION
of propylene from ethylene. The selective production of
propylene to ethylene was initially explored with various
types of zeolites in a continuous fixed-bed reactor. ZSM-5
has stable and low selectivity. However, small-pore zeolite
Zeolites are particularly useful catalysts in industrial
applications. Microcellular networks of zeolite materi-
als provide unique shape selectivity. In particular CHA
3
(
(
chabazite) zeolites with 3-dimensionally 8-membered ring
8-MR) have been used to produce light olefins from
shows high selectivity to ethylene. Therefore, a PTE reac-
tion was carried out using various types of 8-MR zeolite.
The CHA-based SSZ-13 zeolite was studied with regard to
the effect of ethylene selectivity on the PTE reaction. SSZ-
13 zeolite surface modifications of silylation and phospho-
rus have also been systematically studied to ascertain the
relationship between the PTE results and the characteris-
tics of the zeolite.
1
methanol. Light olefins such as ethylene and propy-
lene are the major bulk chemicals currently produced by
the petrochemical industry. These light olefins are used
2
as major petrochemical building blocks for the manu-
facturing of various industrial products, such as packag-
ing, rubber, construction, textiles and furniture, as well
as plastic products. Propylene is a very important raw
material for polypropylene, propylene oxide, and acry-
lonitrile, and is usually produced by means of the naph-
tha cracking process. However, the supply of ethylene
may be deficient (compared with the amounts needed)
in the near future owing to the rapid increase in the
supply of ethylene from ethane crackers and shale gas.
Therefore, the co-production of ethylene and propylene
through the PTE process as a post-process using the above
2
. EXPERIMENTAL DETAILS
2
.1. Preparation of the Catalysts
SSZ-13 was purchased from China Catal. Holding Co.
and SAPO-34, SAPO-17, SAPO-18, and Rho zeolite were
4
–5
prepared in our laboratory. An outer-surface passivat-
ing modification of the SSZ-13-T(X) (X refers to the
TEOS silylation time) catalyst was carried out using
6
1
TEOS (Si(OCH CH ꢀ , Aldrich, 99%) silylation. The
ethylene has attracted much attention recently. In recent
2
3 4
phosphorous-modified SSZ-13 samples were prepared by
the simple impregnation of phosphoric acid in an ethanol
and water mixture. This is referred to here as SSZ-13-
years, chabazite zeolites such as SAPO-34 and SSZ-13
have been reported in relation to the selective production
3
∗
Author to whom correspondence should be addressed.
P(Y) (with Y denoting the P loading amount).
J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 4
1533-4880/2019/19/2183/006
doi:10.1166/jnn.2019.15993
2183

Investigation of the Selective Production of Ethylene from Propylene Over Small-Pore Zeolites
.2. Characterization
Jun et al.
2
Powder X-ray diffraction (XRD) patterns were recorded
on a Rigaku Multiplex instrument using Cu-Kꢁ radia-
tion (ꢂ = 0.15406 nm) operated at 40 kV and 40 mA
(
1.6 kW). Nitrogen physisorption isotherms were mea-
ꢀ
sured at −196 C on a Micromeritics ASAP 2020 instru-
ment. The Si/Al ratios and P loading amounts were
2
determined by inductively coupled plasma-atomic emis-
sion spectroscopy (ICP-AES) using an Optima 4300 DV
instrument (Perkin Elmer). Acid sites were measured
by the temperature-programmed desorption of ammonia
(
NH -TPD) using a BELCAT-M (BEL Japan) instrument.
3
The degree of coke deposition of the catalyst was investi-
gated by recording weight changes on a thermogravimetric
analyzer (DTG-60, Shimadzu).
2
.3. Catalytic Test
The propylene-to-ethylene (PTE) reaction was conducted
in a lab-made fixed-bed reactor system. Pretreatment with
ꢀ
0
.5 g of the catalyst was carried out at 550 C under an N2
flow for 3 h (50 ml/min). The typical PTE reaction was
performed at a weight hourly space velocity (WHSV) of
−1
ꢀ
0
.33 h at 450 C under ambient pressure. The effluent
products were analyzed by an online gas chromatograph
6100GC, Young Lin Instruments, Co.). The conversion
Figure 1. Powder XRD patterns of the 8-MR zeolites with various
structures.
(
of propylene was calculated from the GC-TCD signal of
and their XRD patterns were found to be identical to the
desired zeolitic structures in a comparison with reference
XRD patterns in the IZA database. The specific BET sur-
face areas and total pore volumes of the zeolite materials
with different structures were determined by a nitrogen
physisorption analysis (Table I).
The zeolite materials with various structures underwent
PTE reactions as catalysts at a fixed reaction condition
nitrogen and propylene using an alumina column (50 m×
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
0
ꢃ53 mm I.D.). The light hydrocarbon (carbon number =
Copyright: American Scientific Publishers
C –C ꢀ and heavy hydrocarbon (C ꢀ products generated
1
4
5+
Delivered by Ingenta
from the reaction were analyzed by two GC-FID signals,
one from an alumina column (50 m ×0ꢃ53 mm I.D.) and
the other from a DHA column (100 m ×0ꢃ25 mm I.D.).
ꢀ
−1
of 450 C with a WHSV of 0.33 h . As shown in
Figure 2, the 8-MR zeolite with the 3-D CHA structure,
Rho, shows the steepest decrease in the propylene conver-
sion during the initial reaction period (<2 h). Compared
with SAPO-34, SSZ-13 has a high ethylene yield and high
ethylene selectivity (Figs. 2(b and c)). The 8-MR zeolite
showed relatively gradual deactivation of the catalyst from
3
. RESULTS AND DISCUSSION
3
.1. Effects of the Zeolite Pore Structure on the
PTE Activity
Five zeolite materials in total were prepared to evaluate the
effects of the zeolite pore structure on the PTE. As shown
in Table I, these zeolites are classified according to their
topologies. All of the 8-MR zeolite materials exhibited
distinct XRD peaks with high signal intensities (Fig. 1),
low C3 conversion in the initial reaction period, and the
=
propylene conversion eached a plateau (∼20%) after 7.5 h.
However, the ethylene selectivities of these 8-MR zeolites
exceeded 20% for the entire reaction time (Fig. 2). From
these PTE results of the 8-MR zeolites, the mass transfer
of the reactants and products may not arise, and the pores
may be blocked more easily by the formation of coke due
to the smaller pore channels (cage windows).
Table I. Physicochemical properties of the 8-MR zeolites with various
structures.
b
BET
c
tot
d
S
V
TA
a
2
−1
3
−1
−1
(mmol g )
Zeolites
Topology
Si/Al2
(m g
)
(cm g
)
SAPO-17
SAPO-18
SAPO-34
SSZ-13
Rho
ERI
AEI
CHA
CHA
RHO
0ꢃ03
0ꢃ21
0ꢃ32
27ꢃ8
4ꢃ51
480
532
456
668
552
0.19
0.22
0.42
0.64
0.26
0.42
0.37
1.32
0.95
0.55
3
.2. Effects of a Zeolite Surface Modification on the
PTE Activity
For the further improvement of the PTE activity, the SSZ-
3 zeolite was selected due to a relatively high ethylene
Notes: aSi/Al2 molar ratio obtained from ICP-AES elemental analysis. b BET
BET surface area obtained from N2 adsorption in a relative pressure range (P/P ꢀ
S
is the
1
0
c
d
yield compared to the other 8-MR zeolites. Especially,
to obtain the high ethylene selectivity, we applied the
of 0.05–0.20. Vtot is the total pore volume obtained at P/P0 = 0ꢃ95. TA is the
total acidity obtained from the NH -TPD analysis.
3
2184
J. Nanosci. Nanotechnol. 19, 2183–2188, 2019

Jun et al.
Investigation of the Selective Production of Ethylene from Propylene Over Small-Pore Zeolites
(
a)
(b)
(
c)
Figure 2. Propylene conversion (a), ethylene selectivity (b), and (c) ethylene yield of the 8-MR zeolites with the time-on-stream.
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
Copyright: American Scientific Publishers
passivation of external surface acid sites to theD Se Sl i Zv e- 1r 3e d byi nI n tgh ee nt twa o treated catalysts compared to the commercial
zeolite using treatments of phosphorous and TEOS, which
are typically used to remove acid sites of the outer surface
of small pore zeolites.
H-SSZ-13. These samples also exhibit a lower desorption
temperature at the strong acid sites, indicating the weak-
ened strengths of the acid sites after the TEOS and P treat-
ment. In particular, the significant decrease in the number
of strong acid sites on the catalyst during the TEOS and
P treatment can be attributed to a decrease in the frame-
work Al. The TEOS and P treatment is an effective means
The Si/Al ratios increased significantly after both mod-
2
ifications. Furthermore, from the variation of the BET sur-
face areas of the TEOS and P modified catalysts, as shown
in Table II, it was found that the total surface area of
the parent TEOS and the P-modified catalyst decreased
7
of decreasing the acid amount and acid strength.
2
2
sharply from 668 m /g to 613–633 m /g after the modifica-
tion. From the results shown in Figure 3, it was confirmed
that a decrease in the number of strong acid sites occurred
Table II. Physicochemical properties of surface-modified SSZ-13 zeo-
lites with silylation and phosphorus.
Acid concentration
d
(mmol/g)
a
c
p
S
2
Total
Weak Strong acid site
BET
b
−1
Catalysts
(wt%) Si/Al2 (m g )
H-SSZ-13
–
–
–
0.24
0.52
27.8
35.4
35.9
35.2
36.4
668
0.055 1.261
0.058 0.849
0.056 0.784
0.564 0.816
0.412 0.798
1.32
0.91
0.85
1.38
1.21
SSZ-13-T1
SSZ-13-T2
SSZ-13-P0.25
SSZ-13-P0.5
625
633
613
618
Notes: aꢄ bSi/Al2 molar ratio obtained from the ICP-AES elemental analysis. cSBET
is the BET surface area obtained from N2 adsorption in a relative pressure range
d
(
P/P ꢀ of 0.05–0.20. Acid concentration obtained from the NH -TPD analysis.
Figure 3. NH -TPD pattern of the modified SSZ-13s.
0
3
3
J. Nanosci. Nanotechnol. 19, 2183–2188, 2019
2185

Investigation of the Selective Production of Ethylene from Propylene Over Small-Pore Zeolites
a)
(b)
Jun et al.
(
Figure 4. Propylene conversion (a) and ethylene selectivity (b) of surface-modified SSZ-13 zeolites during the time-on-stream.
In order to investigate the effect of the surface modi-
fication, PTE reactions of the 0.25% and 0.5% P-SSZ-13
catalysts were carried out, as described below. As the con-
tent of P increased, the deactivation occurred more rapidly
at the initial stage of the reaction and at the point of the
maximum ethylene yield. Figure 4 shows the propylene
conversion and ethylene selectivity in the PTE reaction
as a function of time using the surface-modified SSZ-13
zeolites with TEOS and P. The modified SSZ-13 zeolites
exhibited lower propylene conversion and higher ethylene
selectivity than the original SSZ-13 over the entire reac-
tion time. Among these samples, the SSZ-13-T2 showed
the highest ethylene selectivity up to 90%.
As a result, the external surface passivation of SSZ-13
zeolites resulted in an enhanced selectivity towards ethy-
lene in the PTE reaction. In additional, an optimal passiva-
tion treatment could be set for each SSZ-13s zeolite under
investigation.
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
Copyright: American Scientific Publishers
Delivered by Ingenta
Figure 5. Propylene conversion and product selectivities of the SSZ-13-T2 catalyst during the time-on-stream in the regeneration test with air:
Regeneration of (a) fully deactivated and (b) partially deactivated spent samples.
2186
J. Nanosci. Nanotechnol. 19, 2183–2188, 2019

Jun et al.
Investigation of the Selective Production of Ethylene from Propylene Over Small-Pore Zeolites
Figure 6. Propylene conversion and product selectivities of the SSZ-13-T2 catalyst during the time-on-stream in the regeneration test with hydrogen.
3
.3. Regeneration Test
regeneration of the partially deactivated catalyst by air
(dotted red-line), the propane selectivity was always higher
than ethylene selectivity at the initial reaction period
As shown in Figure 5(a) the fully deactivated catalyst
was completely regenerated by the removal of coke from
the cages of the SSZ-13 zeolite. The coke in the zeo-
(
Fig. 5(b)). Figure 6 shows the regeneration of partially
ꢀ
deactivated SSZ-13-T2 catalysts using a hydrogen flow
lite cages were burnt under an air flow 550 C. After
ꢀ
at 500 C. The H regeneration exhibited stable ethy-
2
lene selectivity of around 75∼80% throughout the reaction
time. This occurs because the H partially removed the
2
coke from the cage of the SSZ-13 zeolite. Moreover, there
was no initial induction period after the H regeneration
2
process.
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
For the study of reaction mechanism, three extracted
Copyright: American Scientific Publishers
coke samples from the spent catalysts with different reac-
Delivered by Ingenta
tion times (1.5, 2.5 and 12 h) were prepared for the
GC-MS analysis. As shown in Figure 7, naphthalene is
the main product at the beginning of the reaction (1.5 h);
however naphthalene derivatives and phenanthrene are pro-
duced at the reaction time of 2.5 h. Among the various
naphthalene derivatives produced in this stage, ethyl naph-
thalene would be a main precursor to produce ethylene
via bond cleavage reaction inside cages of the SSZ-13.
These coke analysis results are similar to these of the
spent SSZ-13 catalyst in the ethylene-to-propylene (ETP)
8
reaction. In the proposed reaction mechanism of ETP
reaction, ethylene is rapidly oligomerized and converted
to naphthalene-based intermediates in the cage of SSZ-13.
Among these reaction intermediates, propyl naphthalene
would be the main intermediate to selectively produce
propylene via bond cleavage between naphthalene and
propyl-group. In addition, poly-aromatic and heavier frac-
tions were also formed as the reaction times become
longer. It is due to that these large amount of organic
intermediates and coke formed inside the CHA cages, and
deactivated the catalyst rapidly.
4
. CONCLUSION
SSZ-13 showed the highest ethylene yield among the
-MR zeolites in the PTE reaction. Further surface modi-
8
Figure 7. GC-MS chromatograms (top) and magnified chromatograms
(down) of the extracts from the spent SSZ-13 catalysts.
fication with TEOS or P enhanced the ethylene selectivity
J. Nanosci. Nanotechnol. 19, 2183–2188, 2019
2187

Investigation of the Selective Production of Ethylene from Propylene Over Small-Pore Zeolites
Jun et al.
up to 90% due to the passivation of external acid sites.
Hydrogen regeneration was essential to maintain high
ethylene selectivity without initial induction period. The
analysis of the coke extraction might show the formation
of the ethyl naphthalene intermediate in the SSZ-13 cages,
which was converted to ethylene in the cage of SSZ-13
selectively.
References and Notes
1. J. W. Jun, N. A. Khan, P. W. Seo, C. U. Kim, H. J. Kim, and S. H.
Jhung, Chem. Eng. J. 303, 667 (2016).
2. S. M. Sadrameli, Fuel 173, 285 (2016).
3. J. W. Jun, T. W. Kim, S. I. Hong, J. W. Kim, S. H. Jhung, and C. U.
Kim, Catal. Today http://doi.org/10.1016/j.cattod.2017.10.004.
4. Y. Ji, J. Birmingham, M. A. Deimund, S. K. Brand, and M. E. Davis,
Micro. Meso. Mater. MM 232, 126 (2016).
5. US patent 4,440,871.
6
. P. Losch, M. Boltz, C. Bernardon, B. Louis, A. Pal cˇ i c´ , and
V. Valtchev, Appl. Catal. A: Gen. 509, 30 (2016).
. C. Zhang, X. Guo, C. Song, S. Zhao, and X. Wang, Catal. Today
Acknowledgment: This work was supported by the
National Research Council of Science and Technology
7
8
149, 196 (2010).
(
NST) grant by the Korea government (Ministry of Science
. W. Dai, X. Sun, B. Tang, G. Wu, L. Li, N. Guan, and M. Hunger,
J. Catal. 314, 10 (2014).
and ICT (MSIT)) (No. CRC-14-1-KRICT).
Received: 15 January 2018. Accepted: 13 February 2018.
IP: 5.188.216.173 On: Thu, 06 Dec 2018 12:31:29
Copyright: American Scientific Publishers
Delivered by Ingenta
2188
J. Nanosci. Nanotechnol. 19, 2183–2188, 2019