Vol. 26, No. 24 (2014)
An Effective Process for Removing Acrylonitrile from Wastewater 8573
The purpose of the present study was to investigate the
performance of the catalytic wet air oxidation to acrylonitrile
wastewater and to examine the feasibility of the technology
as a pre-treatment for biological remediation to reduce toxic
organic compound. The effect of the operating conditions on
chemical oxygen demand, total organic carbon and acrylo-
nitrile as well as removal of the acrylonitrile wastewater, inclu-
ding temperature, the concentration of catalyst, time of reaction
and O2 dose were studied. Based on the experimental results,
optimal operating conditions will also be offered.
thymolphthalein to indicate the end, carried out reagent blank
experiment for correction at the same time. acrylonitrile content
is defined as eqn. 1.
Vvitriol − Vblank
X =
× cvitriol × 53000
(1)
Vmaterial
Vvitriol represents the volume of vitriol standard solution during
titration;Vblank represents the volume of vitriol standard solution
used in reagent blank experiment titration;Vmaterial is the volume
of water sample and cvitriol is the concentration of vitriol standard
solution.
EXPERIMENTAL
RESULTS AND DISCUSSION
Characteristics of the acrylonitrile wastewater: Acrylo-
nitrile wastewater used in the experiments was obtained in a
cesspit from the Sinopec Daqing Ltd., China. The wastewater
contains 4000 mg acrylonitrile per liter. The other ingredient
is pure water.
Selection of homogeneous catalyst: Eight metal nitrates
(include no catalyst) used as homogeneous catalyst under the
same reaction condition (523 K, ion concentration 200 mg/L
and O2 dose = 0) after 9 min reaction and their chemical oxygen
demand removal are shown in Table-1. It can be observed from
Table-1 that Cu2+ has the most catalytic efficiency among 8
metal salt solutions. That is because Cu2+ have more catalytic
activity than other metal ions.
The catalytic wet air oxidation of the acrylonitrile waste-
water was carried out in a 0.5 L high pressure batch reactor
(Fig. 1). The reactor was equipped with a magnetically driven
stirrer ensuring good mass transfer from the gas to the liquid
phase and to a catalyst. Firstly, we injected acrylonitrile waste-
water with a given mass of homogeneous catalyst into the
reactor. Secondly, nitrogen flowed through the system to remove
the air within the system; the valves around the reactor were
closed when the air was removed entirely and began to heat.
Finally, pure O2 was introduced into the reactor until the
estimated pressure was reached and the reaction started at the
point called "zero time". Liquid samples (about 50 mL) were
periodically withdrawn from the reactor and analyzed.
TABLE-1
METAL ION AND CHEMICAL
OXYGEN DEMAND REMOVAL (%)
Metal ion
COD removal (%)
76.02
Without catalyst
Cu2+
Ni2+
Fe3+
Zn2+
Mn2+
Co3+
La3+
Ce3+
86.07
79.73
82.71
85.17
76.06
75.67
Safety
valve
Deionied
water tank
Oxidant
tank
79.00
Stirrer
P
76.10
Feed inlet
T
High pressure
pump
Former transition metal ions, such as Ti(IV), Mo(VI),
Fe(IV), Mn(V) take part in the Lewis acid mechanism, during
which the oxidation state of the transition metal ions does not
change and its role as a Lewis acid activated oxidant assist
transfer of active oxygen atom. Key active intermediate of Lewis
acid catalyst include hydrogen peroxide of transition metal
compound (Mn+-OOH), alkyl peroxide compound (Mn+-OOR)
and dioxo compound [Mn+(O2)], where O2 from [Mn+(O2)]
bonding side on the transition metals.
Gas
product
Cooling
water out
Electric
fumace
Heating
wire
Reactor
Cooler
Gas-liquid
Nitrogen separator
cylinder
Cooling
water in
Liquid
product
Temperature
controller
Fig. 1. Schematic diagram of the experimental setup
Latter transition metal ions, especially Cu(II) participate
in oxygen rebound mechanism during catalytic oxidation
process. The oxidation state of transition metal ions changed
and involved in the transfer of active oxygen atoms directly and
its key active intermediate is high-charged transition metal oxo
species, such as Mn+ = O.
Analytical: The chemical oxygen demand of the collected
liquid is measured by potassium dichromate method ofAPHA.
Standard methods for the examination of water and wastewater.
edn 20. Washington, 200013.
The total organic carbon is measured by total organic
carbon determinator "SHIMADZU TOC-L CPN-CN200".
Acrylonitrile content is measured by the sodium sulfite
addition method: Due to the effect of cyano electron-with-
drawing, the double bond of acrylonitrile present high response
performance to nucleophilic reagents. Therefore acrylonitrile
can react with sodium sulfite in water solution, separate out
sodium hydroxide at the same amount of substance, then titrate
the generated sodium hydroxide with 0.1 mol/L vitriol standard
solution and use the indicator mixed by alizarin yellow and
This high-charged species have more catalytic activity
than several compounds above during catalytic oxidation
process, especially oxidation of double and triple bond. Since
the main structures of acrylonitrile being oxidated are C=C
and C=N, therefore, Cu2+ can be used as the homogeneous
catalyst to the reaction.
Catalytic wet air oxidation of the acrylonitrile
Effect of the temperature: Temperature is an important
element affecting the catalytic wet air oxidation of acrylonitrile