Catalysts For Catalytic Wet Oxidation Research Articles

Fracking wastewater treatment: Catalytic performance and life cycle environmental impacts of cerium-based mixed oxide catalysts for catalytic wet oxidation of organic compounds

Water scarcity and the consequent increase of freshwater prices are a cause for concern in regions where shale gas is being extracted via hydraulic fracturing. Wastewater treatment methods aimed at reuse/recycle of fracking wastewater can help reduce water stress of the fracking process. Accordingly, this study assessed the catalytic performance and life cycle environmental impacts of cerium-based mixed oxide catalysts for catalytic wet oxidation (CWO) of organic contaminants, in order to investigate their potential as catalysts for fracking wastewater treatment. For these purposes, MnCeOx and CuCeOx were tested for phenol removal in the presence of concentrated NaCl (200 g L−1), which represented a synthetic fracking wastewater. Removal of phenol in pure (“phenolic”) water without NaCl was also considered for comparison. Complete (100 %) phenol and a 94 % total organic carbon (TOC) removal were achieved in both the phenolic and fracking wastewaters by utilising MnCeOx (5 g L−1) and insignificant metal leaching was observed. However, a much lower activity was observed when the same amount of CuCeOx was utilised: 23.3 % and 20.5 % for phenol and TOC removals, respectively, in the phenolic, and 69.1 % and 63 % in the fracking wastewater. Furthermore, severe copper leaching from CuCeOx was observed during stability tests conducted in the fracking wastewater. A life cycle assessment (LCA) study carried out as part of this work showed that the production of MnCeOx had 12–98 % lower impacts than CuCeOx due to the higher impacts of copper than manganese precursors. Furthermore, the environmental impacts of CWO were found to be 94–99 % lower than those of ozonation due to lower energy and material requirements. Overall, the results of this study suggest that the adoption of catalytic treatment would improve both the efficiency and the environmental sustainability of both the fracking wastewater treatment and the fracking process as a whole.

Reusable Plasma‐Sprayed Transition Metal Oxide Catalyst for Catalytic Wet Oxidation of Organic Waste

AbstractCatalytic wet oxidation (CWO) is an efficient and environmentally friendly method for decomposing organic wastes. This work uses transition metal oxide powders of FeO, MnO2, NiO and the novel mixed oxide Co1.5Mn1.5O4, for plasma‐spraying on stainless‐steel substrates to prepare catalyst plates. These catalysts were used to treat d‐glucose as a model compound for organic waste, using CWO process reactions at temperatures from 150 °C to 170 °C and in the presence of oxygen (20 bar and 40 bar). The catalysts were pre‐oxidised to their suitable phases for better catalytic activity. The plasma‐sprayed Fe2O3 catalysts showed the highest chemical oxygen demand (COD) reduction of 72 %. At high reaction severity the catalyst performances were similar improving the overall performance compared to non‐catalytic wet oxidation reactions. Plasma‐sprayed Fe2O3 was found to be the best catalyst for future CWO trials due to its ability to withstand the reaction severity and acetic acid production.

Use of heterogeneous activated carbon supported copper catalyst for catalytic wet oxidation of biomethanated spent wash: Reaction kinetics, catalyst stability, catalyst deactivation kinetics and biochemical methane potential

In the present study, the potential of activated carbon (AC) supported copper catalyst was investigated during catalytic wet oxidation (CWO) of pretreated high strength biomethanated spent wash (BMSW) stream which is originated from alcohol distillery. Prior to wet oxidation (WO) treatment, the BMSW was centrifuged to remove suspended solids. During CWO treatment at 220 °C temperature, the chemical oxygen demand and color removals of 72% and 97%, respectively, were observed from the centrifuged BMSW (catalyst dose = 3.4 g L−1, reaction time = 3 h). The analysis of treated liquid samples confirmed the formation of acetic acid in large concentrations which is one of the major precursors of methane during post anaerobic treatment. The kinetic expressions for WO and CWO processes were also developed using initial rate method. However, the recovered and regenerated catalyst could only be reused twice in CWO runs. The biochemical methane potential (BMP) test results showed significant production of biogas from the treated BMSW. Based on the findings, it can be inferred that the CWO of BMSW can be a potential treatment method before its disposal in the environment.

Study on heterogeneous catalysts for catalytic wet oxidation

Catalytic wet oxidation is a powerful method for the treatment of high concentration refractory organic wastewater. the support and catalyst components constitute heterogeneous catalysts, and the main catalyst, co-catalyst and co-catalyst components. The main catalyst and co-catalyst are the main influencing factors of the catalyst. The preparation methods of catalyst include precipitation method, impregnation method and impregnation precipitation method. The performance evaluation indexes of heterogeneous catalysts include the activity, stability, selectivity and anti-toxic stability, mechanical stability of the catalysts. according to the principle of chemical transfer, the heterogeneous catalytic reaction process consists of seven steps.

Synthesis of highly active and stable Al/Zr pillared clay as catalyst for catalytic wet oxidation of phenol

Natural bentonite clay was used in the synthesis of single and mixed oxide Al/Zr pillared clay catalysts by means of ultrasonic treatment during the aging and intercalation steps. The raw bentonite and pillared clay catalysts were characterized using high resolution scanning electron microscopy with energy dispersive system (HRSEM-EDS), powder X-ray diffraction (PXRD), N2 adsorption/desorption, Fourier transform infrared spectroscopy, thermogravimetric analysis, cation exchange capacity, zeta potential and all the catalysts evaluated in the catalytic wet air oxidation (CWAO) of phenol. Calcination of the synthesized Al/Zr-PILCs at 500 °C for 120 min yielded optimum physical properties with BET surface area of 230 m2/g, pore volume of 0.115 cm3/g and basal spacing of 1.92 nm and with good thermal stability. Complete removal of phenol was obtained after 120 min and 88% TOC was removed after 180 min in aqueous solution under mild reaction conditions of 100 °C and 10 bar after. Catalyst reusability studies showed that the Al/Zr-PILCs catalyst demonstrated excellent chemical and structural stability with insignificant leaching of Zr4+ after six consecutive catalytic runs. The Al/Zr-PILCs catalyst therefore demonstrated excellent catalytic properties in the CWAO of phenol in aqueous solution.

Bimetallic Ru–Cu as a highly active, selective and stable catalyst for catalytic wet oxidation of aqueous ammonia to nitrogen

Ru/C, Cu/C and bimetallic Ru–Cu/C catalysts are prepared via chemical reduction methods and investigated for catalytic wet oxidation of aqueous ammonia to nitrogen. It is found that the as-prepared bimetallic Ru–Cu/C catalyst is very active and selective as well stable as for selective oxidation of aqueous ammonia toward nitrogen at rather mild conditions. The results show that the Ru–Cu/C catalyst is much more efficient especially stable than the corresponding monometallic Ru/C and Cu/C catalysts, indicating the synergistic effect of Cu and Ru. These catalysts are characterized by XRD, XPS, TEM, and H2-TPR, and the results are revealed that there is strong interaction between Ru and Cu over Ru–Cu/C catalysts and the co-presence of Ru and Cu can effectively adjust the reactivity and converge of oxygen species as well as protect the Ru and Cu from leaching. The strong interaction, synergistic effect, proper oxygen nature and ability against leaching could be attributed to the excellent catalytic property of Ru–Cu/C catalyst.

Catalytic hydrothermal treatment of pulping effluent using a mixture of Cu and Mn metals supported on activated carbon as catalyst.

The present study was performed to investigate the performance of activated carbon-supported copper and manganese base catalyst for catalytic wet oxidation (CWO) of pulping effluent. CWO reaction was performed in a high pressure reactor (capacity = 0.7l) at temperatures ranging from 120 to 190°C and oxygen partial pressures of 0.5 to 0.9MPa with the catalyst concentration of 3g/l for 3h duration. With Cu/Mn/AC catalyst at 190°C temperature and 0.9MPa oxygen partial pressures, the maximum chemical oxygen demand (COD), total organic carbon (TOC), lignin, and color removals of 73, 71, 86, and 85%, respectively, were achieved compared to only 52, 51, 53, and 54% removals during the non-catalytic process. Biodegradability (in terms of 5-day biochemical oxygen demand (BOD5) to COD ratio) of the pulping effluent was improved to 0.38 from an initial value of 0.16 after the catalytic reaction. The adsorbed carbonaceous fraction on the used catalyst was also determined which contributed meager TOC reduction of 3-4%. The leaching test showed dissolution of the metals (i.e., Cu and Mn) from the catalysts in the wastewater during CWO reaction at 190°C temperature and 0.9MPa oxygen partial pressures. In the future, the investigations should focus on the catalyst reusability.

Preparation and Application on High-Efficiency Catalyst for Catalytic Wet Oxidation

The Catalytic Wet Oxidation (CWO) method was investigated to treat phenol cleaning wastewater from chemical container which is difficult dispose with traditional biological methods. In this paper, high-efficiency catalysts were prepared, two methods were used to prepare the catalyst: impregnating, sol-gel. Effects of metal salts concentration, calcination temperature and calcination time on each catalysts performance were explored and optimal catalyst preparation condition was optimized. The results show that the optimum sol-gel condition: Cu / Mn / Ce ratio of 2:2:2, the calcination temperature is 700 °C, calcination time is 5h.; the optimum impregnating condition: Cu / Mn / Ce ratio of 2:2:2, impregnated carrier (AC) of 0.9g/L mixture, the calcination temperature is 300 °C, calcination time is 4h; the sol-gel catalyst has longer service life, the samples prepared by impregnating technique were more active than the samples prepared by sol-gel technique at given reaction conditions.

Catalytic Properties of Cu/13X Zeolite Based Catalyst in Catalytic Wet Peroxide Oxidation of Phenol

Copper bearing 13X zeolite was prepared from commercial 13X zeolite via ion-exchange with copper acetate solutions. After the incorporation of copper, Cu/13X catalyst was exposed to post synthesis thermal treatment at different temperatures. The prepared catalysts were characterized by XRD and FTIR, while the adsorption techniques were used for the measurement of the specific surface area and pore volume. The catalytic tests were carried out in a stainless steel Parr reactor in batch operation mode at atmospheric pressure in temperature range from 333 to 353 K. Influence of postsynthesis thermal treatment and reaction temperature on activity and stability of prepared catalysts in the catalytic wet oxidation process with hydrogen peroxide as oxidant was investigated. The experimental results showed that total degradation of phenol can be achieved under mild operating conditions at temperatures bellow 353 K. All catalysts exhibited higher activity in terms of hydrogen peroxide and phenol abatement with the increasing temperature of the reaction. The postsynthesis thermal treatment resulted in more stable catalyst with respect to stability of both catalysts’ active metal component (copper) and support, while the activity of catalysts in terms of TOC conversion remained unaltered.

Wet oxidation of phenol over transition metal oxide catalysts supported on Ce 0.65Zr 0.35O 2 prepared by continuous hydrothermal synthesis in supercritical water

The mixed oxide (Ce 0.65Zr 0.35O 2) prepared by supercritical synthesis was applied as a support of transition metal (Mn, Fe, Co, Ni, and Cu) oxide catalysts for catalytic wet oxidation (CWO) of phenol in view of their higher thermal stability, better oxygen storage capacity, and higher surface area. The prepared catalysts showed an enhanced catalytic activity for CWO of phenol due to the excellent redox properties of ceria-zirconia mixed oxide. Among the prepared catalysts, the CuO x /Ce 0.65Zr 0.35O 2 was the most effective catalyst in view of catalytic activity and CO 2 selectivity. The leached copper ions seem to contribute to the higher conversion of phenol over the CuO x /Ce 0.65Zr 0.35O 2 via homogeneous catalysis. The characterization with XPS, XANES, and TPR experiments confirmed that the active copper species in the CuO x /Ce 0.65Zr 0.35O 2 is highly dispersed Cu 2+ clusters. Although the MnO x /Ce 0.65Zr 0.35O 2 showed a high conversion of phenol and TOC, the converted phenol was mainly changed to carbon deposits on the surface of catalyst resulting in catalyst deactivation.

Magnesium oxide as an effective catalyst in catalytic wet oxidation of H2S to sulfur

Four different magnesium oxides were studied in the wet oxidation of H2S to sulfur. The H2S removal capacity of MgO in the catalytic wet oxidation strongly depends on the pore size distribution. The MgO with relatively large pores (>100 A) showed a high removal capacity of H2S. It is suggested that the large pore size favors H2S removal in the catalytic wet oxidation due to the limitation of diffusion.

Pd-based catalysts for catalytic wet oxidation of combined Kraft pulp mill effluents in a trickle bed reactor

Catalytic wet oxidation of combined pulp mill effluents was studied in a trickle bed reactor. Two types of supported Pd-based catalysts, eggshell and uniform catalysts, and a supported Pd–Pt uniform catalyst were employed. Supported Pd catalysts showed high activity for total organic carbon (TOC) and color removal at temperatures of 353–448 K and 1.84 MPa. Compared to uniform catalysts, the eggshell catalysts with a 0.2 wt.% Pd loading show promise for treatment of combined pulp mill effluents. High activity for TOC and color removal can be attributed to the high density of active Pd sites in the shell area and to the decrease of diffusion path for reactants and intermediates. No apparent deactivation of eggshell catalysts was observed after 40 h on stream. Potential application of the supported Pd catalysts for treatment of combined pulp mill effluents is discussed.