Enhancing Phenol Conversion Rates in Saline Anaerobic Membrane Bioreactor Using Acetate and Butyrate as Additional Carbon and Energy Sources

Phenolic industrial wastewater, such as those from coal gasification, are considered a challenge for conventional anaerobic wastewater treatment systems because of its extreme characteristics such as presence of recalcitrant compounds, high toxicity, and salinity. However, anaerobic membrane bioreactors (AnMBRs) are considered of potential interest since they retain all micro-organism that are required for conversion of the complex organics. In this study, the degradation of phenol as main carbon and energy source (CES) in AnMBRs at high salinity (8.0 g Na+⋅L–1) was evaluated, as well as the effect of acetate and an acetate-butyrate mixture as additional CES on the specific phenol conversion rate and microbial community structure. Three different experiments in two lab-scale (6.5 L) AnMBRs (35°C) were conducted. The first reactor (R1) was fed with phenol as the main CES, the second reactor was fed with phenol and either acetate [2 g COD⋅L–1], or a 2:1 acetate-butyrate [2 g COD⋅L–1] mixture as additional CES. Results showed that phenol conversion could not be sustained when phenol was the sole CES. In contrast, when the reactor was fed with acetate or an acetate-butyrate mixture, specific phenol conversion rates of 115 and 210 mgPh⋅gVSS–1 d–1, were found, respectively. The syntrophic phenol degrader Syntrophorhabdus sp. and the acetoclastic methanogen Methanosaeta sp. were the dominant bacteria and archaea, respectively, with corresponding relative abundances of up to 63 and 26%. The findings showed that dosage of additional CES allowed the development of a highly active phenol-degrading biomass, potentially improving the treatment of industrial and chemical wastewaters.

In situ organic Fenton-like catalysis triggered by anodic polymeric intermediates for electrochemical water purification

Organic Fenton-like catalysis has been recently developed for water purification, but redox-active compounds have to be ex situ added as oxidant activators, causing secondary pollution problem. Electrochemical oxidation is widely used for pollutant degradation, but suffers from severe electrode fouling caused by high-resistance polymeric intermediates. Herein, we develop an in situ organic Fenton-like catalysis by using the redox-active polymeric intermediates, e.g., benzoquinone, hydroquinone, and quinhydrone, generated in electrochemical pollutant oxidation as H2O2activators. By taking phenol as a target pollutant, we demonstrate that the in situ organic Fenton-like catalysis not only improves pollutant degradation, but also refreshes working electrode with a better catalytic stability. Both1O2nonradical and ·OH radical are generated in the anodic phenol conversion in the in situ organic Fenton-like catalysis. Our findings might provide a new opportunity to develop a simple, efficient, and cost-effective strategy for electrochemical water purification.

The Stabilization of Liquid Smoke through Hydrodeoxygenation Over Nickel Catalyst Loaded on Sarulla Natural Zeolite

Constituents of liquid smoke possess a huge potential to be converted as value-added chemicals, such as flavoring, antiseptics, antioxidants, or even fossil oil substitutes. However, liquid smoke instability, led by the presence of oxygenate compounds, is an obstacle for further utilization and processing. On the other hand, catalyst efficiency in hydrodeoxygenation (HDO) remains challenging. Sarulla natural zeolite (Z), with abundant availability, has not been comprehensively investigated in the catalytic performance of HDO. In this study, Sarulla natural zeolite with different Si/Al ratios, which are activated by several concentrations of hydrochloric acid and nickel supported by Z (Ni-Z) synthesized by wet impregnation, were evaluated for HDO of liquid smoke, particularly in reducing oxygenate compounds. Catalyst morphology, surface area, pores, and crystallinity are investigated. Catalytic performances were evaluated, particularly on reducing oxygenate compounds and the shifting of phenol and its derivatives. Furthermore, the liquid smoke product of HDO was analyzed by gas chromatography-mass spectrometry (GC-MS). The data obtained reveal that the HDO process of liquid smoke with the Z3 catalyst shows the best activity compared to Z5 and Z7, with phenol conversion of 62.39% and 11.93% of alkoxy reduction. Meanwhile, the best Ni metal catalyst system activity was given by the Ni-Z5 catalyst compared to Ni-Z3 and Ni-Z7, where phenol conversion and alkoxy reduction were at 60.06% and 11.49%, respectively.

Enhanced Degradation of Phenol by a Fenton-Like System (Fe/EDTA/H2O2) at Circumneutral pH

This work deals with the degradation of phenol based on the classical Fenton process, which is enhanced by the presence of chelating agents. Several iron-chelating agents such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA), and ethylenediamine-N,N’-diacetic acid (EDDA) were explored, although particular attention was given to EDTA. The effect of the molar ligand to iron ratio, EDTA:Fe, initial pH, and temperature on the oxidation process was studied. The results demonstrate that the proposed alternative approach allows the capacity for degrading phenol to be extended from the usual acidic pH (around 3.0) to circumneutral pH range (6.5–7.5). The overall feasibility of the process depends on the concentration of the chelating agent and the initial pH of the solution. The maximum phenol conversion, over 95%, is achieved using a 0.3 to 1 molar ratio of EDTA:Fe, stoichiometric ratio of H2O2 at an initial pH of 7.0, and a temperature of 30 °C after 2 hours of reaction, whereas only 10% of phenol conversion is obtained without EDTA. However, in excess of ligand (EDTA:Fe > 1), the generation of radicals seems to be strongly suppressed. Improvement of the phenol removal efficiency at neutral pH also occurs for the other chelating agents tested.

Differences in the Catalytic Behavior of Au-Metalized TiO2 Systems During Phenol Photo-Degradation and CO Oxidation

For this present work, a series of Au-metallized TiO2 catalysts were synthesized and characterized in order to compare their performance in two different catalytic environments: the phenol degradation that occurs during the liquid phase and in the CO oxidation phase, which proceeds the gas phase. The obtained materials were analyzed by different techniques such as XRF, SBET, XRD, TEM, XPS, and UV-Vis DRS. Although the metallization was not totally efficient in all cases, the amount of noble metal loaded depended strongly on the deposition time. Furthermore, the differences in the amount of loaded gold were important factors influencing the physicochemical properties of the catalysts, and consequently, their performances in the studied reactors. The addition of gold represented a considerable increase in the phenol conversion when compared with that of the TiO2, despite the small amount of noble metal loaded. However, this was not the case in the CO oxidation reaction. Beyond the differences in the phase where the reaction occurred, the loss of catalytic activity during the CO oxidation reaction was directly related to the sintering of the gold nanoparticles.

Liquid Phase Selective Hydrogenation of Phenol to Cyclohexanone over Electrospun Pd/PVDF-HFP Catalyst

Cyclohexanone is an important industrial intermediate in the synthesis of materials such as nylons, but preparing it efficiently through one-step hydrogenation of phenol is hindered by over-reduction to cyclohexanol. Using an efficient catalyst can enhance the selectivity of cyclohexanone at high phenol conversion. In this study, catalysts comprised of palladium nanoparticles supported on electrospun PVDF-HFP (polyvinylidene fluoride-co-hexafluoropropylene) nanofibers were prepared using the electrospinning technique. The catalysts were characterized using thermogravimetric analyzer (TGA), scanning electron microscopy (SEM), transmission electron microscope (TEM), and drop shape analyzer (DSA). The prepared catalysts were used to hydrogenate phenol into cyclohexanone in a batch reactor. The Pd/PVDF-HFP catalyst showed a very high product selectivity and high phenol conversion. The conversion of phenol achieved was 98% with 97% cyclohexanone selectivity in 7 h using 15 wt% of palladium (0.0021 moles) relative to phenol (0.0159 moles). The turnover number (TON) and turnover frequency (TOF) values calculated were 7.38 and 1.05 h−1, respectively. This paper presents original research in heterogeneous catalysis using novel electrospun nanofibers. Multiphase hydrogenation of phenol to cyclohexanone over electrospun Pd/PVDF-HFP catalyst has not been reported by any researcher in the literature. This work will also provide a research window for the application of electrospun polymeric nanofibers in multiphase reactions.

Hierarchical ZSM-5 Zeolite with Enhanced Catalytic Activity for Alkylation of Phenol with Tert-Butanol

Using polyethylene glycol as a mesoporous soft template, a series of hierarchically porous ZSM-5 zeolites were prepared. X-ray diffraction, infrared spectroscopy, N2 adsorption–desorption, and transmission electron microscopy results demonstrated that the resultant materials contained a micro–mesoporous structure. Since the existence of mesoporous structure favors the diffusion of large molecular reactants and products, the phenol conversion and selectivity to 2,4-Di-TBP on the hierarchical ZSM-5 zeolite can be improved for the alkylation of phenol with tert-butanol.

Synthesis and characterization of binary and ternary hydrotalcites-like compounds for the hydroxylation of phenol

Hydrotalcites (HT) and hydrotalcites-like (HTLc) compounds were synthesized by the co-precipitation method under low supersaturation. The synthesized binary Mg-Al hydrotalcites and ternary Cu/Mg-Al hydrotalcite-like compounds were characterized by various physico-chemical techniques such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (XRD), Fourier transform- infrared spectroscopy (FT-IR), ultraviolet-visible (UV-VIS) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area analysis. Elemental composition generated from ICP-OES data revealed a value of x in the region of 0.25 to 0.33 for all the compounds except for the MgAl-11 sample which revealed an x value of 0.5 while XRD patterns exhibited characteristic features indicative of an ordered layered material. FT-IR spectra confirmed the presence of characteristic functional groups and interlayer anions. Only Cu2+ which has a d9 configuration was accountable for the bands identified in UV-VIS spectra, whereas both Mg and Al with their d0 electron configurations showed no absorptive bands in the UV-VIS spectra. During thermal treatment by TGA, typical weight loss of Cu-Mg/Al HTLcs with temperature elevation was observed. The SEM images clearly demonstrated that all the Cu-Mg/Al HTLcs retained their characteristically layered structure morphologies. The BET surface area measurements showed no trend, however the surface area decreased with an increase in the copper concentration in some cases. For the heterogeneous hydroxylation of phenol using H2O2 as an oxidant, several reaction parameters such as solvent systems, catalyst amount, temperature, substrate/oxidant ratio, time and solvent volume were investigated. The product stream, monitored by gas chromatography showed that catechol (CAT) and hydroquinone (HQ) were the main products. Non-catalytic (blank) experiments were investigated to determine whether the reactants and the internal standard contributes to the conversion of phenol without the use of a catalyst. All blank reactions showed very low phenol conversions which were less than 1%, whereas the Mg/Al HTs showed low phenol conversions as well. All the Cu-Mg/Al catalysts showed measurable phenol conversion with Cu-Mg/Al-51a giving the highest conversion of 29.9% and a 56 and 44% selectivity towards CAT and HQ, respectively. The Cu-Mg/Al-15b catalyst, which had the lowest copper concentration, showed the lowest phenol conversion of 8.3% with a 55 % CAT selectivity and 45% HQ selectivity. In general, the phenol conversion increased with an increase in copper concentration. This reinforced the hypothesis that copper was the active centre in this reaction, since no measurable conversion was observed with Mg/Al HTs.

Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts

<p>The ZSM-5, g-Al₂O₃, SiO₂ and MgO supported Pd-catalysts were prepared for the phenol hydrogenation to cyclohexanone in liquid-phase. The natures of these catalysts were characterized by XRD, N₂ adsorption-desorption analysis, H₂-TPR, CO₂-TPD and NH₃-TPD. The catalytic performance of the supported Pd-catalyst for phenol hydrogenation to cyclohexanone is closely related to nature of the support and the size of Pd nanoparticles. The Pd/MgO catalyst which possesses higher basicity shows higher cyclohexanone selectivity, but lower phenol conversion owing to the lower specific surface area. The Pd/SiO₂ catalyst prepared by precipitation gives higher cyclohexanone selectivity and phenol conversion, due to the moderate amount of Lewis acidic sites, and the smaller size and higher dispersion of Pd nanoparticles on the surface. Under the reaction temperature of 135 ^oC and H₂ pressure of 1 MPa, after reacting for 3.5 h, the phenol conversion of 71.62% and the cyclohexanone selectivity of 90.77% can be obtained over 0.5 wt% Pd/SiO₂ catalyst. Copyright © 2016 BCREC GROUP. All rights reserved</p><p><em>Received: 7^th March 2016; Revised: 13^rd May 2016; Accepted: 7^th June 2016</em></p><p><strong>How to Cite:</strong> Fan, L., Zhang, L., Shen, Y., Liu, D., Wahab, N., Hasan, M.M. (2016). Liquid-phase Hydrogenation of Phenol to Cyclohexanone over Supported Palladium Catalysts. <em>Bulletin of Chemical Reaction Engineering &amp; Catalysis</em>, 11 (3): 354-362 (doi: 10.9767/bcrec.11.3.575.354-362)</p><p><strong>Permalink/DOI</strong>: <a href="http://doi.org/10.9767/bcrec.11.3.575.354-362">http://doi.org/10.9767/bcrec.11.3.575.354-362</a></p>