Continuous and complete conversion of high concentration p-nitrophenol in a flow-through membrane reactor
Summary (2 min read)
Introduction
- P-Nitrophenol (PNP) is a common environmental pollutant in water and is therefore a great public concern.
- It is usually used as a precursor or a synthetic intermediate in the industrial manufacturing of analgesics, pharmaceuticals, insecticides, dyes and other chemicals.
- Therefore, the complete elimination of this compound from industrial effluents is a matter of concern for environmental protection.
- The conventional physical methods (sedimentation, filtration, adsorption, etc.) transfer the contaminants into other forms and cannot solve the waste disposal problem.
- 15,16 Conventional metal-acid reduction methods employ reagents such as iron-acids or tin-acids.
Preparation of catalytic membranes
- Synthesis of TiO2 nanorods and branched TiO2 nanorods on ceramic membranes TiO2 nanorod arrays on sheet Al2O3 ceramic membranes (circular, 3.2 cm in diameter, 1.6 mm in thickness and 30% in porosity) were obtained via the following two-step hydrothermal method.
- 26 Twenty mL of concentrated hydrochloric acid (Analytical Reagent, This article is protected by copyright.
- Hydrothermal synthesis was initiated when the autoclave was placed in an electric oven and maintained at 150°C for 5 hours.
- Chloride ions can accelerate the growth of TiO2 in the direction of the top (001) crystal facet.29.
- The branched TiO2 nanorod-modified ceramic membranes were further modified with N-(β-aminoethyl)-γ-aminopropyl trimethoxy silane by immersing them in 50 mL of This article is protected by copyright.
Characterization of Catalytic Membranes
- The crystal structure of the catalytic membranes was determined by X-ray diffraction (XRD, Miniflex-600) analysis at a scan rate of 10° per min in the range of 5-70°.
- The surface morphology of the catalytic membranes was characterized using a field emission scanning electron microscope (FESEM, Hitachi S-4800II).
- Area of the catalytic membranes was measured by N2 physisorption using a physical adsorption apparatus (Micromeritics, ASAP 2020).
- The pore size of the catalytic membranes was determined using a mercury intrusion porosimeter (Poremaster GT-60).
Pd nanoparticles in catalytic membranes
- EDS mapping was performed on the three catalytic membranes to investigate the distribution of elemental Pd. In Figure 4, the red dots represent the Pd signal.
- The distribution of Pd on the surface of Pd/BTiO2-CM is particularly dense and uniform, confirming that modification with branched TiO2 nanorods can provide additional available surface for the loading of Pd nanoparticles.
- As expected, the total quantity of Pd in the reactor consisting of the Pd/BTiO2-CM is the highest (3 mg).
- Taking into account of the errors of measurement, the average diameters of Pd nanoparticles in the three catalytic membranes are almost the same (about 4.2 nm).
- The decline in the PNP conversion using Pd/CM and Pd/BTiO2-CM were 15.6% and 8.4%, which are less than the leaching percentage of Pd.
Evaluation of Catalytic Performance
- Reduction of PNP was performed in a flow-through membrane reactor system in two modes (cycle mode and continuous mode).
- Samples of the reaction mixture were taken from the sampling port in intervals of 5 minutes and were analyzed by high-performance liquid chromatography (HPLC, Agilent 1200 series).
- The flow rate of the reaction mixture through the reactor system was controlled by the peristaltic pump.
- Furthermore, in order to improve the catalytic efficiency, two membrane modules were connected in series.
Characterization of catalytic membranes
- As illustrated in Figure 2, the diffraction lines of Pd/TiO2-CM and Pd/BTiO2-CM show similar patterns.
- Compared to Pd/TiO2-CM, the diffraction peaks of TiO2 relative to the Al2O3 peaks are more intense with the Pd/BTiO2-CM due to the higher coverage density of TiO2 on the ceramic membrane after synthesis of branches.
- Pd in the XRD patterns, which may be attributed to the low content and high dispersion of Pd nanoparticles.
- The morphology of the branched TiO2 nanorods obtained after 16 hours of treatment is shown in the image of Pd/BTiO2-CM.
Conclusions
- In summary, a novel flow-through catalytic membrane reactor system was designed and constructed for the continuous complete conversion of high concentration p-nitrophenol.
- The This article is protected by copyright.
- Modification of ceramic membranes with branched TiO2 nanorods can enhance the Pd content but renders parts of the Pd nanoparticles unusable.
- High concentrations of p-nitrophenol can be completely converted with less consumption of NaBH4 in a short time in the flow-through catalytic membrane reactor, which can be attributed to the small Pd nanoparticles, a higher Pd content and rapid mass transfer.
- The conversion efficiency remained at 100% for 240 minutes, and no byproducts were detected.
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Frequently Asked Questions (17)
Q2. What have the authors contributed in "Continuous and complete conversion of high concentration p-nitrophenol in a flow-through membrane reactor" ?
Here, the authors 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.
Q3. What is the important chemical intermediate for the conversion of PNP?
Catalytic reduction of PNP to p-aminophenol, an important chemical intermediate, is afeasible method for turning waste into a renewable resource.
Q4. What is the promising process for the conversion of PNP?
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.
Q5. What is the potential of the catalytic membrane reactor?
The catalytic membrane reactor developed here provides a promising prospect for practical applications of industrial wastewater treatment.
Q6. How long did the membrane remain in ethanol?
Once the reaction process was completed (60 minutes for each run), the catalytic membrane was removed and immersed in ethanol for 1 hour, then applied to the next reaction.
Q7. What is the effect of the flow-through mode on the catalytic efficiency of the membrane?
In future work, the authors will attempt to further reduce the amount of NaBH4, enhance the catalytic efficiency of Pd and the stability of the catalytic membrane, and improve the economic efficiency of the catalytic membrane reactor.
Q8. How was the surface area of the catalytic membrane in contact with the reactant?
The surface area of the catalytic membrane in contact with the reactant solution was 8.04 cm2 and the thickness of the catalytic membrane was 0.16 cm.
Q9. What is the total residence time of the reaction solution in the two successive catalytic membranes?
The total residence time of the reaction solution in the two successive catalytic membranes is defined as:residence time (s) = pore volume of membranes (cm3)volumetric flow rate of reaction solution (cm3/s)This article is protected by copyright.
Q10. What is the reason for the improvement of catalytic activity?
the authors can deduce that modification with branched TiO2 nanorods can effectively increase the surface area, resulting in increased loading amounts of Pd, which is one of the reasons for the improvement of catalytic activity.
Q11. What are the features of the flow-through catalytic membrane reactor?
These features indicate that the reaction solution can more easily pass through the membrane and contact the active sites in the pores in their research, resulting in enhanced catalytic efficiency23.
Q12. What is the effect of the synthesis of TiO2 nanorods on the ceramic membrane?
In this work, the synthesis of TiO2 nanorods and branched TiO2 nanorods on the ceramic membranes makes the membrane pore size decrease (Table 1), leading to the reduced water flux.
Q13. How many particles were tested in a triplicate?
To obtain reproducible results, the particle size of the Pd was evaluated by counting more than 100 particles and samples were tested in triplicate.
Q14. What are the advantages of flow-through catalytic membrane reactors?
These advantages allow flow-through catalytic membrane reactors to efficiently treat industrial wastewaters that contain high concentrations of PNP.
Q15. What is the way to reduce PNP?
the direct reduction of PNP with NaBH4 as a reducing agent is considered to be an efficient and greener catalytic route for the conversion of PNP.
Q16. How much is the conversion efficiency of PNP in the first run?
For Pd/CM, after 5 cycles, the conversion efficiency of PNP was only 74.0%, which is significantly lower than that in the first run (87.7%).
Q17. How long can PNP be reduced in a flow-through membrane reactor?
it can be concluded that the contaminant PNP can be continuously and thoroughly reduced to p-aminophenol within 240 min in a flow-through membrane reactor.