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Journal ArticleDOI

Continuous and complete conversion of high concentration p-nitrophenol in a flow-through membrane reactor

01 Sep 2019-Aiche Journal (Wiley)-Vol. 65, Iss: 9

Abstract: Here, we report on a green and effective method for the continuous and complete conversion of high concentrations of p-nitrophenol (PNP) using a flow-through membrane reactor and less NaBH4 The catalytic membrane was successfully fabricated by loading Pd nanoparticles onto the surface of a branched TiO2 nanorod-functionalized ceramic membrane The modification with branched TiO2 nanorods can significantly improve the loading amount of Pd nanoparticles onto ceramic membranes, resulting in enhanced catalytic performance With 6 mg of Pd, 93 L m−2 hr−1 of flux density and 804 cm2 of membrane surface area in the flow-through membrane reactor, PNP at a concentration of 4,000 ppm can be converted to high-value p-aminophenol using less NaBH4 (using a molar ratio of NaBH4:PNP of 96) within 24 s at 30°C More importantly, the conversion can be continuously and stably performed for 240 min
Topics: Ceramic membrane (59%), Membrane reactor (57%), Membrane (56%)

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REACTION ENGINEERING, KINETICS AND
CATALYSIS
AIChE Journal
DOI10.1002/aic.16692
Continuous and complete conversion of high concentration p-nitrophenol
in a flow-through membrane reactor
Jianfeng Miao, Jia Lu, Hong Jiang, Yefei Liu and Weihong Xing
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University,
Nanjing 210009, P.R. China
Xuebin Ke*
School of Engineering and Computer Science, University of Hull, HU6 7RX, United
Kingdom
Rizhi Chen*
State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University,
Nanjing 210009, P.R. China
*Corresponding author. X.Ke@hull.ac.uk; rizhichen@njtech.edu.cn
This article has been accepted for publication and undergone full peer review but has not been through
the copyediting, typesetting, pagination and proofreading process which may lead to differences between
this version and the Version of Record. Please cite this article as doi: 10.1002/aic.16692
© 2019 American Institute of Chemical Engineers
Received: Jan 14, 2019;Revised: May
23, 2019;Accepted: Jun 04, 2019
This article is protected by copyright. All rights reserved.
This is the peer reviewed version of the following article: Miao, J, Lu, J, Jiang, H, et al. Continuous and complete
conversion of high concentration p-nitrophenol in a flow-through membrane reactor. AIChE J. 2019;e16692, which has
been published in final form at https://doi.org/10.1002/aic.16692. This article may be used for non-commercial
purposes in accordance With Wiley Terms and Conditions for self-archiving.

Abstract
Here, we report on a green and effective method for the continuous and complete
conversion of high concentrations of p-nitrophenol (PNP) using a flow-through membrane
reactor and less NaBH
4
. The catalytic membrane was successfully fabricated by loading Pd
nanoparticles onto the surface of a branched TiO
2
nanorod-functionalized ceramic membrane.
The modification with branched TiO
2
nanorods can significantly improve the loading amount
of Pd nanoparticles onto ceramic membranes, resulting in enhanced catalytic performance.
With 6 mg of Pd, 93 L·m
-2
·h
-1
of flux density and 8.04 cm
2
of membrane surface area in the
flow-through membrane reactor, PNP at a concentration of 4000 ppm can be converted to
high-value p-aminophenol using less NaBH
4
(using a molar ratio of NaBH
4
:PNP of 9.6)
within 24 seconds at 30
o
C. More importantly, the conversion can be continuously and stably
performed for 240 minutes.
Keywords: p-Nitrophenol, continuous and complete conversion, Pd nanoparticles, branched
TiO
2
nanorods, flow-through membrane reactor
This article is protected by copyright. All rights reserved.

Introduction
p-Nitrophenol (PNP) is a common environmental pollutant in water and is therefore a
great public concern.
1
It is usually used as a precursor or a synthetic intermediate in the
industrial manufacturing of analgesics, pharmaceuticals, insecticides, dyes and other
chemicals.
2-4
PNP may bring about significant health hazards because of its carcinogenic
toxicity. Short-term inhalation or ingestion in humans can cause headaches, drowsiness,
nausea and cyanosis, even at low concentrations.
5,6
The concentration of PNP in industrial
wastewater is usually much higher than 500 mg/L.
7
Therefore, the complete elimination of
this compound from industrial effluents is a matter of concern for environmental protection.
Various methods have been proposed for the treatment of PNP-contaminated wastewater.
8
The conventional physical methods (sedimentation, filtration, adsorption, etc.) transfer the
contaminants into other forms and cannot solve the waste disposal problem.
9
Biological
methods may require long treatment time, and complete degradation may be impossible,
This article is protected by copyright. All rights reserved.

especially for effluents containing PNP at a high concentration.
10-12
Thus, the development of
effective chemical methods to convert PNP to high-value products or to achieve complete
degradation is urgently needed.
Catalytic reduction of PNP to p-aminophenol, an important chemical intermediate, is a
feasible method for turning waste into a renewable resource.
13,14
In addition, aromatic amines
are less toxic and considerably easier to mineralize than their corresponding
nitroaromatics.
15,16
Conventional metal-acid reduction methods employ reagents such as
iron-acids or tin-acids.
The major disadvantage of such reduction processes is the generation
of large amounts of metal oxide sludge that is associated with severe pollution problems.
17
One-step hydrogenation of PNP in the presence of metal catalysts or supported metal
catalysts is considered to be the most promising process because of its high efficiency and
environmentally friendly properties.
18
As a strong reducing agent, NaBH
4
can effectively
reduce PNP to p-aminophenol under mild operation conditions (room temperature and
atmospheric pressure).
19
Thus, the direct reduction of PNP with NaBH
4
as a reducing agent is
considered to be an efficient and greener catalytic route for the conversion of PNP.
In the practical treatment of industrial wastewater, fixed-bed reactors and slurry reactors
inevitably develop problems. For a fixed-bed reactor, fine catalysts cannot be directly used,
and their inner surface cannot be fully utilized. In addition, the regeneration and replacement
of catalysts are inconvenient. In a slurry reactor, metal nanoparticles that are present on the
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powdered catalysts easily aggregate or leak, and it is difficult to separate them from the
reaction system.
20
Catalytic membranes exhibit good particle distribution, and no additional
separation is required.
21,22
Moreover, the porous membrane structure and flow-through mode
can enhance the catalytic efficiency by increasing mass transfer.
23
These advantages allow
flow-through catalytic membrane reactors to efficiently treat industrial wastewaters that
contain high concentrations of PNP. Wang et al.
24
developed a novel poly (vinylidene fluoride)
membrane with Pd/poly (methacrylic acid) microspheres immobilized inside the membrane
pores. Its use in the catalytic reduction of PNP indicated that a conversion of 99.8% could be
achieved in a cross-flow model. Domènech et al.
25
reported on the synthesis of Pd
nanoparticles in sulfonated polyethersulfone membranes. The catalytic performance was
evaluated by following the reduction of PNP in the presence of NaBH
4
. Greater than 90% of
the PNP was reduced within 4 hours using a single reaction step, and deactivation was
observed after consecutive catalytic cycles. Our group
26
successfully demonstrated that the
use of TiO
2
nanorod-functionalized ceramic membranes is an effective approach for
enhancing the loading amount of Pd and the corresponding catalytic activity. However, the
catalytic membranes obtained when used directly in a batch reactor could not achieve
continuous conversion of PNP. Furthermore, although complete conversion of PNP can be
achieved, a high molar ratio of NaBH
4
to PNP like 100 is required.
27,28
An excess of the
reductant NaBH
4
will increase the treatment cost significantly. Therefore, the efficient
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References
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Sheng-Peng Sun1, Ann T. Lemley1Institutions (1)
Abstract: Heterogeneous Fenton-like reactions on nano-magnetite (Fe 3 O 4 ) were investigated for the degradation of p-Nitrophenol (p-NP). A four factor central composite design (CCD) coupled with response surface methodology (RSM) was applied to evaluate and optimize the important variables. A significant quadratic model ( P -value R 2 = 0.9442) was derived using analysis of variance (ANOVA), which was adequate to perform the process variables optimization. Optimum conditions were determined to be 1.5 g L −1 Fe 3 O 4 , 620 mM H 2 O 2 , pH 7.0 and 25–45 mg L −1 p-NP. More than 90% of p-NP was experimentally degraded after 10 h of reaction time under the optimum conditions, which agreed well with the model predictions. The results demonstrated that the degradation of p-NP was due to the attack of hydroxyl radicals ( OH) generated by the surface-catalyzed decomposition of hydrogen peroxide on the nano-Fe 3 O 4 , i.e. heterogeneous Fenton-like reactions. Possible mechanisms of p-NP degradation in this system were proposed, based on intermediates identified by LC–MS and GC–MS and included benzoquinone, hydroquinone, 1,2,4-trihydroxybenzene and p-nitrocatechol. The kinetic analysis implied that the generation rate of OH ( V OH ) was increased along with the degradation of p-NP. This was attributed to the formation of acidic products, which decreased the solution pH and enhanced the decomposition of absorbed hydrogen peroxide via a radical producing pathway on the nano-Fe 3 O 4 surface.

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Abstract: Monodisperse spherical titania particles of variable sizes are produced in a sol−gel synthesis from Ti(EtO)4 in ethanol with addition of a salt or a polymer solution. The influence of different salt ions or polymer molecules on the size and the size distribution of the final particles was investigated. The amorphous hydrous titania particles were characterized by electron microscopy, thermogravimetry, 1H-MAS NMR, X-ray absorption spectroscopy, and electrophoresis. Nitrogen absorption measurements revealed that the addition of polymers yields hollow and porous titania colloids.

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Abstract: Nitrobenzene (NB) is a toxic compound that is often found as a pollutant in the environment. The present removal strategies suffer from high cost or slow conversion rate. Here, we investigated the conversion of NB to aniline (AN), a less toxic endproduct that can easily be mineralized, using a fed-batch bioelectrochemical system with microbially catalyzed cathode. When a voltage of 0.5 V was applied in the presence of glucose, 88.2 ± 0.60% of the supplied NB (0.5 mM) was transformed to AN within 24 h, which was 10.25 and 2.90 times higher than an abiotic cathode and open circuit controlled experiment, respectively. AN was the only product detected during bioelectrochemical reduction of NB (maximum efficiency 98.70 ± 0.87%), whereas in abiotic conditions nitrosobenzene was observed as intermediate of NB reduction to AN (decreased efficiency to 73.75 ± 3.2%). When glucose was replaced by NaHCO(3), the rate of NB degradation decreased about 10%, selective transformation of NB to AN was still achieved (98.93 ± 0.77%). Upon autoclaving the cathode electrode, nitrosobenzene was formed as an intermediate, leading to a decreased AN formation efficiency of 71.6%. Cyclic voltammetry highlighted higher peak currents as well as decreased overpotentials for NB reduction at the biocathode. 16S rRNA based analysis of the biofilm on the cathode indicated that the cathode was dominated by an Enterococcus species closely related to Enterococcus aquimarinus.

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Abstract: In this study, aerobic granules to treat wastewater containing p-nitrophenol (PNP) were successfully developed in a sequencing batch reactor (SBR) using activated sludge as inoculum. A key step was the conditioning of the activated sludge seed to enrich for biomass with improved settleability and higher PNP degradation activity by implementing progressive decreases in settling time and stepwise increases in PNP concentration. The aerobic granules were cultivated at a PNP loading rate of 0.6 kg/ m3 x day, with glucose to boost the growth of PNP-degrading biomass. The granules had a clearly defined shape and appearance, settled significantly faster than activated sludge, and were capable of nearly complete PNP removal. The granules had specific PNP degradation rates that increased with PNP concentration from 0 to 40.1 mg of PNP/L, peaked at 19.3 mg of PNP/(g of VSS) x h (VSS = volatile suspended solids), and declined with further increases in PNP concentration as substrate inhibition effects became significant. Batch incubation experiments show that the PNP-degrading granules could also degrade other phenolic compounds, such as hydroquinone, p-nitrocatechol, phenol, 2,4-dichlorophenol, and 2,6-dichlorophenol. The PNP-degrading granules contained diverse microbial morphotypes, and PNP-degrading bacteria accounted for 49% of the total culturable heterotrophic bacteria. Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments showed a gradual temporal shift in microbial community succession as the granules developed from the activated sludge seed. Specific oxygen utilization rates at 100 mg/L PNP were found to increase with the evolution of smaller granules to large granules, suggesting that the granulation process can enhance metabolic efficiency toward biodegradation of PNP. The results in this study demonstrate that it is possible to use aerobic granules for PNP biodegradation and broadens the benefits of using the SBR to target treatment of toxic and recalcitrant organic compounds.

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