Hydrocarbon Processing - November 2021 - 58

Sustainability
reduced by ~20%, wastewater and solid
waste are reduced by more than 70%, and
no tail gas emissions are produced. The
slurry bed technology has obvious advantages
in economy, greenness, intrinsic
safety and productivity.
Green production technology for
CPL. As the monomer for nylon-6 fiber
and engineering plastics, CPL is an important
basic organic chemical that is
widely used in textile, automobile, electronics
and other industries. More than
90% of CPL worldwide is manufactured
by the rearrangement of cyclohexanone
oxime. This route mainly includes hydrogenation
of benzene to cyclohexane,
oxidation of cyclohexane to cyclohexanone,
ammoximation of cyclohexanone
to cyclohexanone oxime, rearrangement
of cyclohexanone oxime to CPL, and the
subsequent multi-step refining processes.
Traditional CPL production technology
drawbacks include:
1. Cyclohexanone oxime is
synthesized by cyclohexanone
hydroxylamine oxidation,
which involves the oxidation
of ammonia to NOx
, the
absorption and reduction of
NOx to hydroxylamine, and
the reaction of hydroxylamine
and cyclohexanone to produce
cyclohexanone oxime. This
process is complex with only 60%
utilization of ammonia. During
the whole process, noble metal
catalyst is consumed, and highly
toxic NOx
is produced.
2. Cyclohexanone oxime to
CPL adopts the liquid-phase
Beckmann rearrangement
technology. Fuming sulfuric acid
is used as the catalyst, resulting in
serious equipment corrosion and
a large production of low-valued
ammonium sulfate.
3. Unstable Raney nickel is used in
the CPL purification process. This
hydrogenation process is complex
with a high catalyst consumption
and low hydrogenation efficiency.
In view of the above deficiencies of
traditional CPL production technology,
the green CPL production technology
developed by the authors' company provides
solutions:
1. A direct cyclohexanone
ammoximation technology with
cyclohexanone, H2
O2 and NH3
,
in which hollow TS-1 zeolite is
used as the catalyst and H2
O is the
only byproduct. This technology
integrates micro-sized hollow
TS-1 zeolite with a slurry bed
reactor fitted with a membrane
separation component. A good
mass transfer performance of
the reaction system has been
developed. The micro-sized
hollow TS-1 zeolite is prepared
by hydrothermal synthesis
with secondary structural
modification technology,
and its stability is improved
by adding silicon-containing
additives.8,9,10
In this direct
cyclohexanone ammoximation
technology, the cyclohexanone
conversion is more than 99.9%,
and the cyclohexanone oxime
selectivity is more than 99.5%.
The new technology markedly
simplifies the cyclohexanone
ammoximation process, improves
the utilization of NH3
from 60%
to > 90%, decreases the plant
investment by > 70%, reduces
99.5% of exhaust emissions, and
eliminates the production or use
of corrosive NOx
. As a result, the
production cost of cyclohexanone
oxime is reduced by 800 CNY·t−1
.
2. A gas-phase Beckmann
rearrangement of cyclohexanone
oxime to CPL by integrating
silicalite-1 zeolite with a movingbed
reactor.11,12
The use of fuming
FIG. 2. A 400-kt·a-1
CPL industrial production plant. Source: Sinopec.
TABLE 1. Comparison of different technologies for H2
Technology
Working
liquid
Slurry bed (authors' company) AR+TOP+EAQ
Fixed-bed
AR+TOP+EAQ
O2 production
Hydrogenation
efficiency, g·L-1
12-13
7-8
Working liquid loss,
kg·tH2O2
-1
2.03
2.54
Energy consumption,
kWh·tH2O2
-1
600
742
Regeneration
Acid, safe
Al2
O3
,
explosion risk
Note: AR, heavy aromatics; TOP, trioctyl phosphate; TBU, tetrabutyl urea; 2-MCHA, o-methyl cyclohexyl acetate; EAQ, ethyl anthraquinone; AAQ, amyl anthraquinone
58 NOVEMBER 2021 | HydrocarbonProcessing.com
Capacity,
10 kt·a-1
12
5
sulfuric acid is avoided, and no
ammonium sulfate is produced.
As a result, there is no equipment
corrosion nor pollutant
emissions. The cyclohexanone
oxime conversion is higher than
99.9%, and the CPL selectivity
is around 96.5%. The nitrogen
atom utilization is increased
from 36% to near 100%. The
production cost can potentially
be reduced by 1,000 CNY·t−1
.

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Hydrocarbon Processing - November 2021

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