Nitrogen-Doped Carbon-Assisted One-pot Tandem Reaction for Vinyl Chloride Production via Ethylene Oxychlorination

Article abstract of DOI:10.1002/ange.202006729

A bifunctional catalyst comprising CuCl₂/Al₂O₃ and nitrogen-doped carbon was developed for an efficient one-pot ethylene oxychlorination process to produce vinyl chloride monomer (VCM) up to 76 % yield at 250 °C and under ambient pressure, which is higher than the conventional industrial two-step process (≈50 %) in a single pass. In the second bed, active sites containing N-functional groups on the metal-free N-doped carbon catalyzed both ethylene oxychlorination and ethylene dichloride (EDC) dehydrochlorination under the mild conditions. Benefitting from the bifunctionality of the N-doped carbon, VCM formation was intensified by the surface Cl*-looping of EDC dehydrochlorination and ethylene oxychlorination. Both reactions were enhanced by in situ consumption of surface Cl* by oxychlorination, in which Cl* was generated by EDC dehydrochlorination. This work offers a promising alternative pathway to VCM production via ethylene oxychlorination at mild conditions through a single pass reactor.

Full text of DOI:10.1002/ange.202006729

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Titel: N-doped Carbon Assisted One-pot Tandem Reaction for Vinyl
Chloride Production via Ethylene Oxychlorination
Autoren: Hongfei Ma, Guoyan Ma, Yanying Qi, Yalan Wang, Qingjun
Chen, Kumar Ranjan Rout, Terje Fuglerud, and De Chen
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Zitierweise: Angew. Chem. Int. Ed. 10.1002/anie.202006729
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10.1002/ange.202006729
Angewandte Chemie
RESEARCH ARTICLE
N-doped Carbon Assisted One-pot Tandem Reaction for Vinyl
Chloride Production via Ethylene Oxychlorination
Hongfei Ma,[a] Guoyan Ma,[b] Yanying Qi,[a] Yalan Wang,[a] Qingjun Chen,[a] Kumar R. Rout,[a, c] Terje
Fuglerud,[d] and De Chen*[a]
[a]
H. Ma, Dr. Y. Qi, Dr. Y. Wang, Dr. K. R. Rout, Prof. Dr. D. Chen
Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), Sem sælands vei 4, 7491, Trondheim, Norway.
E-mail: de.chen@ntnu.no
[b]
Dr. G. Ma
College of Chemistry and Chemical Engineering, Xi’an Shiyou University, Xi’an 710065, Shaanxi, China.
Shaanxi Key Laboratory of Carbon Dioxide Sequestration and Enhanced Oil Recovery (under planning), Xi’an 710065, Shaanxi, China.
Dr. K. R. Rout
Sintef Industry, Sem sælands vei 2A, 7491, Trondheim, Norway.
T. Fuglerud
[c]
[d]
INOVYN, Herøya Industrial Park, 3936, Porsgrunn, Norway
Supporting information for this article is given via a link at the end of the document.
Abstract: Herein, we demonstrated a bifunctional catalyst design
concept of CuCl2/Al2O3 and N-doped carbon for an efficient one-pot
ethylene oxychlorination process to produce VCM up to 76% yield at
250 °C and ambient pressure, higher than the conventional industrial
two-step process (~50%). In addition to the CuCl2/Al2O3-based
ethylene oxychlorination catalyst in the first bed, we demonstrated the
active sites containing N-functional groups on the metal-free N-doped
carbon in the second bed catalyzed both ethylene oxychlorination and
ethylene dichloride (EDC) dehydrochlorination at the mild conditions.
Benefit from the bi-function of the N-doped carbon, the VCM formation
was intensified by the surface Cl*−looping of EDC
dehydrochlorination and ethylene oxychlorination. Both reactions
were enhanced by in-situ consumption of surface Cl* by
oxychlorination, in which Cl* was generated by EDC
dehydrochlorination. This work paves a promising alternative way for
VCM production via ethylene oxychlorination at mild conditions
through a single pass reactor.
formation presented the main challenges in the EDC cracking for
the VCM production. The impurities such as butadiene and methyl
chloride etc. generated by high-temperature radicals’ reactions
must be controlled at a very low level due to the requirement of
plant operation. Coke formation at the high-temperature cracker
tubes is one key parameter influencing the production cost. The
complexity of the process drives a search for simplifying the
process to produce VCM directly from C2H4, O2, and HCl in a
single pass reactor.[1a, 2a, 3]
The ethylene oxychlorination is typically catalyzed by a
promoted CuCl2/Al2O3-based catalyst at relatively low
temperatures (ca. 220−250 °C) and 2−6 bar.[4] It is not feasible to
integrate the low-temperature oxychlorination and high-
temperature EDC thermal cracking together, which loses the
CuCl2/Al2O3-based catalyst stability at high temperatures or
reduces the activity of EDC dehydrochlorination at low
temperatures. Efforts have been devoted to developing new
catalysts such as lanthanum (oxy)chloride, and CeO2 with bi-
function of oxychlorination and dehydrochlorination for a high-
temperature process to directly produce VCM.[3, 5] However, these
catalysts are not active at low temperatures, the typical ethylene
oxychlorination conditions around 220−250 ˚C. Highly active bi-
functional catalysts at low temperatures are highly desired.
In the present work, we report an energy-efficient process to
produce VCM from ethylene oxychlorination at relatively low
temperatures on a metal-free carbon catalyst. To the best of our
knowledge, for the first time, a metal-free carbon-based catalyst
was reported having the catalytic activity for ethylene
oxychlorination to directly produce VCM at a relatively low
temperature of 250 °C. We found that the N-doped carbon
catalyst not only catalyzes the ethylene oxychlorination but also
facilitates the EDC dehydrochlorination reaction due to the
bifunctional ability. The oxychlorination−dehydrochlorination
process was integrated into one dual-bed single pass reactor,
where ethylene oxychlorination catalysts were followed by N-
doped carbon catalysts, at a low temperature (250 °C) to achieve
a high VCM yield up to 76%, even higher than the one in the
current industrial single-pass balanced VCM process. The one-
pot process has been remarkably intensified by a synergic effect
between the oxychlorination and dehydrochlorination reactions at
the same type of active site by the surface Cl* looping between
the two reactions.
Introduction
Polyvinyl chloride (PVC) is the most versatile of all thermoplastics
that can be used in a wide range of applications. It is the third-
highest volume polymer, slightly behind polyethylene and
polypropylene.[1] Vinyl chloride (VCM), the monomer of PVC is the
key building block for PVC production, which is mainly produced
from ethylene dichloride (EDC) through thermal cracking.
Currently, approximately 90% of VCM production plants
worldwide are using a balanced VCM process where Cl2 by first
chlorinating ethylene to produce EDC, the EDC is then thermally
converted to VCM by dehydrochlorination.[1a] The HCl produced
in the dehydrochlorination reactor is typically captured and
recycled to an oxychlorination reactor to convert C2H4, O2, and
HCl to EDC, which is again converted to VCM by
2]
dehydrochlorination.[1a,
The balanced VCM process is a
complex multi-process including three reaction sections,
separation and recycle Besides, EDC
unites.[2]
dehydrochlorination also called EDC cracking, is an energy-
intensive process, which is carried out at high temperatures
(500−550 °C), high pressures (15−20 bar), at a conversion of
approximately 50−60% leading to an overall VCM yield about
50% in a single pass.[1a, 3] The control of impurities and coke
1
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10.1002/ange.202006729
Angewandte Chemie
RESEARCH ARTICLE
Results and Discussion
C2H4Cl2 → C2H3Cl + HCl, ΔH=73.0 kJ/mol
C2H4 + 0.5O2 + HCl → C2H3Cl + H2O, ΔH= -166.7 kJ/mol
(2)
(3)
Inspired by the reported high activity in the acetylene
hydrochlorination and EDC dehydrochlorination reactions,[6] N-
doped carbon was chosen for testing the VCM synthesis. The N-
doped mesopores carbon was synthesized by polymerization with
melamine (M) as the nitrogen precursor, phenol (P), and
formaldehyde (F) as the carbon source, using SiO2 colloid as a
hard template following the carbonizations and removal of the
templates. To achieve different N contents, different precursor
compositions (Nx, x stands for the mol ratio of M/P) were used.
The morphologies of the N-doped mesopores carbon were
characterized by the high-resolution TEM, as shown in Figure1,
BET (Figure S1 and Table S1), and XRD (Figure S2). The very
broad diffraction peaks on the XRD patterns indicated the
amorphous structure and no obvious structural difference with the
different N-contents.[7] Raman spectra show typical characteristic
D and G bands of disordered graphitic materials (Figure S3), the
intensity ratios of ID/IG increased with increasing the N content,
indicating the increased defectiveness. Thus, from XRD and
Raman, it can be concluded that doping N can introduce disorder
in the graphitic structure. The mesopores with the diameters
range of 10−50 nm are observed on the N0.5 catalyst. From the
TEM-mappings of the carbon catalysts (Figure S4−S6), N was
introduced into the mesopores carbon, and it is highly dispersed
in the carbon, which contributed to the high specific surface area
and pore volume.[8] The introduction of N into the carbon was also
confirmed by the XPS analysis. A high-resolution XPS scan was
applied to shed light on the N species in the mesopores carbon,
as shown in Figure 1d and S7. The deconvolution of the N1s
spectra of N0.5 indicated that three N-species existed in the
mesopores carbon corresponding to pyridinic N, pyrrolic N,
graphitic N,[8] as shown in Table S2, and S3, where the pyridinic
N and pyrrolic N are the most portions.
Ethylene oxychlorination, EDC dehydrochlorination, and VCM
direct formation from ethylene oxychlorination are presented in
Eqs. 1−3. Thermodynamic calculations for the reactions 1-3 were
performed as shown in Figure S8. EDC dehydrochlorination
reaction (Eq. 2) is highly endothermic and Gibbs free energy is
negative only at higher temperatures (>~250 °C). The ΔrG is
highly negative for reaction Eq. 3 leading to direct VCM formation,
which is combined reactions of 1 and 2, suggesting the reaction
highly thermodynamically favorable.
The catalyst testing was performed in a fixed-bed reactor at
250 °C using the stoichiometric C2H4: O2: HCl ratio of 2:1:2
following the reaction (Eq. 3) on N-doped carbon catalysts (N0.5
and N3). The conversion and product distribution are presented
in Figure 2, compared to the carbon catalyst without N-doping
(N0). The carbon catalyst (N0) is almost inactive, while metal-free
N-doped carbon is highly active for ethylene oxychlorination direct
to EDC and VCM. Based on our best knowledge, this is the first
time to observe the metal-free N-doped carbon catalyst active for
C2H4 oxychlorination and make it possible for a one-pot synthesis
of VCM at low temperatures. The metal-free catalyst has a
remarkably higher low-temperature activity compared to
Lanthanide compounds which are typically active only at
temperatures higher than 400 °C.[5] The metal-free catalyst is
highly stable and no changes in the activity and selectivity were
observed during the 40 h time on stream (Figure S9). The main
products are VCM, EDC, byproducts of COx (CO and CO2), and
other chlorinated products, where VCM is dominating. The
selectivity depends on the N content and selectivity to VCM
(~50%) on N0.5 is highest among the catalysts tested.
(a)
(b)
(c)
(d)
Figure 2. Catalytic results of the N-doped carbon for ethylene
oxychlorination. Reaction conditions: C2H4/O2/HCl=2:1:2, 250 °C,
Wcat=0.8 g, gas hour space velocity: 4350 ml/h·gcat, FC 4 =4
H
2
ml/min, Ptotal=1 bar.
Given the unprecedented activity of N-doped carbon for both
oxychlorination and dehydrochlorination, kinetic study, and
various temperature-programmed desorption (TPD) and
temperature-programmed surface reactions (TPSR) were
performed to elucidate the reaction network, reaction mechanism,
and active sites.
Figure 1. a) TEM image and c) elemental mapping of N0.5; b)
XPS survey scan and d) high-resolution N1s spectra of N0.5.
C2H4 + 0.5O2 + 2HCl → C2H4Cl2 + H2O, ΔH= -239.7 kJ/mol
(1)
2
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10.1002/ange.202006729
Angewandte Chemie
RESEARCH ARTICLE
Figure 3. TP-X profiles for all the N-doped catalysts, Ptotal= 1 bar, Wcat=0.5 g, 10 °C/min. a) HCl-TPD, FAr=100 ml/min. b) C2H4/O2 TPSR
after saturated adsorbing of HCl. The signal of VCM was recorded, Ftotal=100 ml/min, FC 4=10 ml/min, C2H4/O2=2, diluted in Ar. c)
H
2
EDC-TPSR with HCl recorded by MS, FAr=100 ml/min.
The HCl−TPD (Figure 3a) illustrated the adsorbed amount of
HCl increases with increasing the N content. Without N-doping,
only a very weak desorption peak at 175 °C was observed. It
rationalizes that almost no activity observed on the neat carbon
surface. When it is doped with N, not only the desorbed amount
of HCl increased but also the desorption temperature shifts to
higher ones with increasing with N content, suggesting stronger
adsorption of HCl on catalysts with the higher content of N. DFT
calculation suggested chemisorption of HCl on N groups forming
N−H−Cl.[9] The acidic strength follows an order of pyridinic
>pyrrolic >graphitic N groups, and the graphitic N does almost not
contribute to the basicity of the catalyst.[10] The higher N content,
the more HCl was desorbed with higher desorption temperature,
possibly attributed to the higher number of the pyridinic N sites
(Table S4) with stronger basicity.[10a] Ethylene TPD (Figure S10)
suggests the ethylene can adsorb rather strongly on the carbon
surface. The literature suggests also that oxygen can be strongly
adsorbed on the carbon surface.[11]
the basicity. Combining the facts of more EDC adsorbed, more
VCM formed, and the lower starting temperature of the TPSR of
EDC on N3 compared to N0.5 and N0, the activity of EDC
dehydrochlorination follows the order of the N content. When
looking at the number of N species (Table S4), both pyridinic and
graphitic N contents increased with increasing N content. Owing
to the very weak basicity of graphitic N, it can be proposed that
pyridinic N groups with the highest basicity among the N groups
could be the main active sites for EDC dehydrochlorination.
The selectivity vs. conversion plot (Figure S11) suggests EDC is
an unstable primary product, while VCM is the primary product
plus the secondary product from EDC dehydrochlorination. The
possible contribution of Cl2 from the Deacon reaction (4HCl + O2=
2Cl2 + 2H2O) to EDC formation was excluded experimentally
(Section S5 in supporting information).
The reactivity of adsorbed HCl was checked by the TPSR of
C2H4/O2 on HCl saturated surfaces, as shown in Figures 3b, S12,
and S13. VCM was produced dominatingly on the N-doped
carbon catalyst in addition to HCl and ethyl chloride (Figure S12,
The active site requirement is further examined by analyzing
the contributions of different N groups to the catalytic performance. S13); while no VCM was detected on the N0 catalyst. Moreover,
Although, several methods have been reported for synthesis N-
doped carbon catalysts,[12] multiple types of N species were often
introduced simultaneously. It makes the identification of active
sites in N-doped carbon very challenging. However, the fact that
the higher N content (N3) yielded a lower reaction rate than N0.5
(Figures 2 and 3b) suggests that the ethylene oxychlorination is
not directly related to the total N content. As we discussed above,
three N groups exist and the distribution of the N groups varies
with the catalysts (Figure 1d, S7, Tables S3−5). We normalized
the reaction rate of ethylene oxychlorination based on the number
of three N-species, as shown in Table S5. Only the normalized
ethylene conversion rates based on the pyrrolic-N group are
similar, and others have almost two orders of magnitude
difference. It suggests that the pyrrolic N might be a highly
relevant active site for the ethylene oxychlorination, which is
similar to the previous reports[6a, 6d] that the pyrrolic N sites on N-
doped carbon catalysts contribute mainly to the acetylene
hydrochlorination.
TPSR of ethylene in the absence of oxygen on the HCl saturated
adsorbed surfaces produced only ethyl chloride (EC) (Figure S14).
EC is also an unstable primary product in ethylene oxychlorination
(Figure S11). However, the possible contribution in VCM
formation by the oxidative dehydrogenation of EC has been
excluded by the reaction of EC and oxygen, which formed mainly
ethylene instead of VCM (Figure S15). A comparison between
TPSR of C2H4/O2 and TPSR of C2H4 reveals that oxygen is
essential to provide the surface Cl* for chlorinating ethylene to
EDC, which is most likely obtained from the oxidative dissociation
of the adsorbed HCl*. The VCM is also a product of the catalytic
dehydrochlorination of EDC, which was evidenced by TPSR of
EDC where the adsorbed EDC was selectively converted to VCM,
(Figure 3c). By summarizing all the results, a reaction mechanism
is proposed, and a detailed discussion of the reaction mechanism
can be seen in the supporting information (section 5). The
catalytic cycle leading to EDC and VCM on the N-doped carbon
surface is presented in Figure 4.
The exact active site for catalytic EDC dichlorination on N-
doped carbon is still in debate, where pyridinic and pyrrolic N or
pyridinic and graphitic N groups as main active sites have been
reported.[13] The activity of EDC dehydrochlorination depends on
3
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10.1002/ange.202006729
Angewandte Chemie
RESEARCH ARTICLE
COx at the reaction conditions was eliminated by the temperature-
programmed oxidation of the N-doped carbon, no CO2 was
detected until 400 °C (Figure S16). It indicated that the catalyst
materials can be stable at the reaction condition (250 °C). It is well
known that certain surface oxygen groups on the carbon surface
can catalyze the deep oxidation to lead COx formation.[11, 15] The
challenge on selectivity to COx on carbon-based catalysts has
long been documented in a similar type of redox reaction such as
oxidative dehydrogenation of hydrocarbons. The oxygen
functional groups on N0.5 were characterized by the high-
resolution O1s XPS scan as shown in Figure S17. The peaks
were assigned to C−O with the binding energies of ~532.6 eV and
C=O with the binding energy of ~531.3 eV. The C=O surface
oxygen groups have been recognized as the main group
contributing to the overoxidation of the reactants and products in
the presence of oxygen molecules to form the COx.[15d] It should
be noted that N-doped carbon has not been optimized further and
the material could be modified by P or B to reduce the formation
of COx.[11]
Based on the above analysis, lowering the oxygen
concentration in the gas phase exposing to the carbon surface
could potentially reduce the COx formation. A tandem reaction on
a bi-functional catalyst strategy was then proposed and tested,
where the CuCl2/Al2O3-based oxychlorination catalyst and the N-
doped carbon are installed together. The promoted CuCl2/Al2O3
catalysts are typical industrial catalysts for EDC production.[1a]
The Ce-promoted CuCl2/Al2O3 catalyst has been reported to be
active and stable for the ethylene oxychlorination.[4e] Figure 5
shows very high selectivity to EDC of above 99%, and no VCM
on the Ce-promoted CuCl2/Al2O3 catalyst, which is consistent with
the previous report.[4e] The activity of CuCl2/Al2O3 catalysts is
higher compared to the N-doped carbon catalyst, N0.5 (Figure 5).
In addition to high activity for ethylene oxychlorination, N-doped
carbon showed also high activity, selectivity, and stability for EDC
dehydrochlorination (Figure S18), in good agreement with
literature observations.[6b, 13] No deactivation was observed during
the 12 h at 250 °C for EDC dehydrochlorination on the N0.5
catalyst.
Figure 4. Scheme of the reaction cycles in direct produce VCM in
a single step from ethylene oxychlorination on the N-doped
carbon catalyst.
The metal-free N-doped carbon catalyst has the redox activity
for ethylene oxychlorination as well as the activity for the
dehydrochlorination. The catalyst surface has bi-functionality and
both reactions can occur on the same type of active site. The
reaction follows a Langmuir−Hinshelwood mechanism. All the
reactants, C2H4, HCl, and O2 adsorbed on the surface. The
adsorbed HCl oxidatively dissociates to form the surface Cl*. The
surface Cl* chlorinated the adsorbed ethylene to form adsorbed
EDC, which can be desorbed to gas-phase EDC or further go to
dehydrochlorination. The EDC dehydrochlorination involves C−H
and C−Cl cleavage to form surface H* and Cl*.[14] Results of VCM
being the primary product of oxychlorination, full conversion to
VCM in TPSR of C2H4/O2, and VCM formed in TPSR of EDC
reveal a Cl* loop between the ethylene oxychlorination and EDC
dehydrochlorination, instead of a gas phase HCl loop. The surface
Cl* generated by EDC* dehydrochlorination directly participates
in the ethylene oxychlorination. Therefore, both EDC and VCM
are primary products.
Two bi-functional catalyst configurations, namely a physical
mixture of two catalysts and dual-bed with CuCl2/Al2O3 catalysts
at the top following the N0.5 catalyst, are tested for the tandem
reactions. As shown in Figure 5, the tandem reactions on the
physically mixed catalysts reduced significantly the COx
selectivity. However, only 23% selectivity of VCM was obtained,
and the EDC is still the main product. Moreover, the conversion
on the mixed bed lowered about 8% of the sum of the conversion
from the individual CuCl2/Al2O3 and N-doped carbon beds. It can
be ascribed by the strong adsorption of the chloride-containing
compounds such as VCM on the CuCl2-based catalyst surface,
suppressing the oxychlorination reaction, shown in Figure S19. In
the dual-bed configuration, the high selectivity of VCM of about
70% and low selectivity to COx (~6%) were obtained. Part of the
O2 was consumed in the oxychlorination reaction on CeCu/Al2O3,
and oxygen concentration is relatively low in the second catalyst
layer, confirmed the above hypothesis of decreasing the COx
formation by reducing the oxygen concentration exposed to the
carbon surface. A VCM yield of 45.6% at a C2H4 conversion of
63.7% was obtained at 250 °C and 1 bar, which is comparable to
the current industrial single-pass two-step process as discussed
above. Furthermore, the C2H4 conversion on the dual-bed
catalysts is much higher than that on the physical mixture of the
Figure 5. Catalytic results in comparison (CeCu/Al2O3 at the top,
N0.5 at the bottom) at the same flow rate. Reaction conditions:
C2H4/O2/HCl=2:1:2, 250 °C, CeCu: 0.2 g, N0.5: 0.8 g, for physical
and dual bed: catalysts mass 0.2 (CeCu) + 0.8 (N0.5) g, FC
4 ml/min, Ptotal=1 bar.
=
4
H
2
However, the N-doped carbon catalyst has a drawback with
relatively high selectivity of COx. The possible contribution of the
oxidation of the N-doped carbon catalyst itself in the formation of
4
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10.1002/ange.202006729
Angewandte Chemie
RESEARCH ARTICLE
catalysts, and even slightly higher than the sum of the conversion
on the neat CeCu/Al2O3 and the N-doped carbon catalysts.
Moreover, the VCM selectivity is much higher in the dual bed
compared to the physical mixture. The enhanced ethylene
conversion in the dual-bed is ascribed to the synergy of the EDC
dehydrochlorination and ethylene oxychlorination on the bi-
functional N-doped carbon surface. In the first catalyst bed, the
most of HCl was consumed by ethylene oxychlorination, while in
the second catalyst bed both the EDC dehydrochlorination and
ethylene oxychlorination were coupled together on the N-doped
carbon surface through the surface Cl* loop, generating a synergy
effect between the two reactions. The effects of the N species of
the N-doped carbon in the second layer on the performance of the
dual-bed catalysts are presented in Figures S20 and 21.
VCM/EDC ratio follows an order of N0.5 >N3 >N0, in good
agreement with the activity order of ethylene oxychlorination on
the same type of catalysts. The multifunctionality, relatively high
number of pyrrolic and pyridinic species of N0.5 makes it possible
to effectively combine both the ethylene oxychlorination and EDC
dehydrochlorination reactions on the surface to lead a high yield
of VCM.
VCM yield is expected to be further optimized through the
modification of N-doped carbon catalysts.
Conclusion
We report here a metal-free N-doped carbon as an efficient
bifunctional catalyst of ethylene oxychlorination and EDC
dehydrochlorination for the synthesis of VCM and EDC at low
temperatures (around 250 °C). The pyrrolic and pyridinic N were
proved to be the main active sites on the N-doped carbon for
ethylene oxychlorination and EDC dehydrochlorination,
respectively. A reaction mechanism with surface Cl* looping
between ethylene oxychlorination and EDC dehydrochlorination
was proposed to rationalize the observed synergy effect of the
two reactions. Moreover, we demonstrated an efficient one-pot
dual-bed bifunctional catalyst concept to produce VCM up to 76%
at mild conditions of 250 °C, 1 bar, and a stoichiometric C2H4: O2:
HCl ratio of 2: 1: 2, much higher (ca. 25%) than the one in the
current two-step industrial process. In the first bed, CuCl2/Al2O3-
based catalyst catalyzes the ethylene oxychlorination, while in the
second bed N-doped carbon coupled both ethylene
oxychlorination and EDC dehydrochlorination reactions together
on the surface. The metal-free N-doped carbon catalysts are
believed to have significant impacts on VCM-related studies for
both academia and industry toward a more cost and energy
effective VCM production process.
Acknowledgments
This work was supported by the iCSI (industrial Catalysis Science
and Innovation) center, which receives financial support from the
Research Council of Norway under the grant No. 237922. G. Ma
acknowledges the funding by Open Foundation of Shaanxi Key
Laboratory of Carbon Dioxide Sequestration and Enhanced Oil
Recovery (under planning) with the contract No. of
YJSYZX20SKF0002.
Figure 6. Catalytic results of the dual-bed method (CeCu/Al2O3 at
the top, N0.5 at the bottom) with different mass ratios at the same
conditions: (A) 1:1; (B) 1:4; (C) 1:9, (D) 1:2; (E) 1:5, with the total
mass of 1 g for A, B, C; 1.2 g for D and E. Reaction conditions:
Keywords: Carbon •Ethylene oxychlorination • Heterogeneous
catalysis • Industrial chemistry • Vinyl chloride
C2H4/O2/HCl=2:1:2, 250 °C, FC
= 4 ml/min, Ptotal=1 bar.
4
[1]
a) A. Boulamanti, J. Moya, Publications Office of the European Union
2017; b) A. Gamble, The Charleston Advisor 2019, 20, 46-50; c) H. Ma,
Y. Wang, Y. Qi, K. Rout, D. Chen, ACS Catal. 2020, 10, 9299-9319.
a) M. E. Jones, M. M. Olken, D. A. Hickman, US Patent, 6909024B1,
2005; b) M. R. Flid, Catal. Ind. 2010, 1, 285-293.
H
2
Moreover, the bi-functionality of the N-doped carbon leads to
the direct production of VCM from the ethylene oxychlorination. In
principle, it breaks down the constrain of the chemical equilibrium
of the EDC dehydrochlorination at low temperatures. Therefore,
the tandem reaction using bi-functional N-doped carbon can
intensify reactions toward VCM formation at relatively low
temperatures. The tandem reaction was then optimized to
enhance the yield of VCM by tuning the mass ratio of the two
catalysts in the dual-bed, as shown in Figure 6. Conditions A, B,
and C are varying the ratio with the total mass kept. The results
clearly showed that more N-doped carbon catalyst in the reactor,
the higher the VCM selectivity is. The higher VCM yield of 60%
due to a higher conversion of ethylene and selectivity to VCM at
the condition E was obtained. Further increase the residence time
the VCM yield increased up to 75.7% (Table S6), with the C2H4
conversion of 94.8%. The results revealed that the VCM yield
depends on the residence time and the ratio of the catalysts. The
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RESEARCH ARTICLE
Entry for the Table of Contents
VCM was directly produced by a metal-free N-doped carbon catalyst in one step via the ethylene oxychlorination process at 250 °C. It
integrates the ethylene oxychlorination and high temperature-dehydrochlorination reactions into one single pass with remarkable
conversion and selectivity. By efficiently design the combination of the tandem reaction, a VCM yield high as the current two-step
process can be obtained at the mild conditions.
7
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