湿式氧化催化剂的研究

摘要叙述了一型湿式氧化催化剂的研制情况和用于处理工业废水的效果,给出了有关小型试验结果。     

Catalytic wet air oxidation of low molecular weight carboxylic acids using a carbon supported platinum catalyst

Aqueous solutions of low molecular weight carboxylic acids, such as acetic, propionic and butyric acids, were treated by catalytic wet air oxidation (CWAO) using a carbon supported platinum catalyst. Oxidation in the presence of the catalyst, in a stirred reactor, was carried out at 200°C and 6.9 bar of oxygen partial pressure, with conversions (after 2 h) ranging from 59.4 to 75%, and selectivities to gaseous products of up to 100%. Initial rates for conversion varied from 184 (butyric acid) to 260 mmol h⁻¹ g_Pt⁻¹ (propionic acid). The activation energy for butyric acid conversion was found to be 56.7 kJ mol⁻¹.     

Reaction pathway of the catalytic wet air oxidation of phenol with a Fe/activated carbon catalyst

Catalytic wet air oxidation (CWAO) of phenol with molecular oxygen using a home-made Fe/activated carbon catalyst at mild operating conditions (100–127 °C; 8 atm) has been studied in a trickle-bed reactor. Ring compounds (hydroquinone, p-benzoquinone and p-hydroxybenzoic acid) and short-chain organic acids (maleic, malonic, oxalic, acetic and formic) have been identified as intermediate oxidation products. CWAO experiments using each one of these intermediates as starting compound have been carried out (at 127 °C and 8 atm) in order to elucidate the reaction pathway. It was found that phenol is oxidized through two different ways. It can be either para-hydroxylated to hydroquinone, which is instantaneously oxidized to p-benzoquinone or para-carboxylated to p-hydroxybenzoic acid. p-Benzoquinone is majorly mineralized to CO₂ and H₂O through oxalic acid formation whereas p-hydroxybenzoic acid gives rise to short-chain acids. Only acetic acid showed to be refractory to CWAO under the operating conditions used in this work. The catalyst avoids the presence of ring-condensation products in the reactor effluent which were formed in absence of it. This is an additional important feature because of the ecotoxicity of such compounds.     

Catalytic wet air oxidation of acetic acid over different ruthenium catalysts

Ruthenium catalysts were prepared by impregnation of different supports: ZrO₂, CeO₂, TiO₂, ZrO₂–CeO₂ and TiO₂–CeO₂. Their activities for acetic acid oxidation in aqueous solution were investigated in a stirred reactor at a reaction temperature of 200 °C and total pressure of 4 MPa. The order of the catalyst activity obtained was RuO₂/ZrO₂–CeO₂ > RuO₂/CeO₂ > RuO₂/TiO₂–CeO₂ > RuO₂/ZrO₂ > RuO₂/TiO₂, which corresponds to surface concentration of non-lattice oxygen (defect-oxide or hydroxyl-like group) of these catalysts. The non-lattice oxygen on the catalyst surface plays an important role in the catalytic activity.     

常温常压催化湿式氧化中Mo-Mn-Al-O催化剂的制备及活性

以Mn-Al-O为载体,钼酸盐为活性成分的前驱体,采用共沉淀-浸渍法制备出Mo-Mn-Al-O催化剂,使用ICP-OES、BET、XRD和XPS方法对其进行表征,研究其在常温常压下催化湿式氧化阳离子型染料废水的催化活性。实验结果表明,Mo的浸渍浓度为1.5 mol·L^-1、浸渍温度为55℃、焙烧时间为3 h和焙烧温度为400℃下制备出的Mo-Mn-Al-O催化剂对阳离子红GTL、阳离子红X-GRL、阳离子黄X-GL和阳离子蓝X-BL都有较好的催化性能。特别是,当催化剂投加量为2.72 g·L^-1时,反应1 h后对阳离子红GTL的脱色率和TOC去除率分别达到74.8%和64.5%。     

Characterizations of platinum catalysts supported on Ce, Zr, Pr-oxides and formation of carbonate species in catalytic wet air oxidation of acetic acid

Catalytic wet air oxidation (CWAO) of aqueous solution of acetic acid (78 mmol L⁻¹) was carried out with pure oxygen (2 MPa) at 200 °C in a stirred batch reactor on platinum supported oxide catalysts (Pt/oxide, oxide = CeO₂, Zr_0.1Ce_0.9O₂, Zr_0.1(Ce_0.75Pr_0.25)_0.9O₂ and ZrO₂). Platinum was loaded on oxides by impregnation (5 wt%), and then the catalysts were reduced under H₂. Homogenous dispersions of 2–3 nm metal crystallites were obtained. The catalytic activity depended on the ability of the support to resist to the formation of carbonates. Ce(CO₃)OH species, determined by FT-IR and XRD, were rapidly formed during the CWAO reaction especially on mixed oxides. These carbonates were responsible to a drastic drop in catalytic performances. Amounts of carbonate species increase with the ability of the catalyst to transfer oxygen.     

Rectorite as catalyst for wet air oxidation of phenol

Rectorite was characterized by XRF, BET, XRD, FT-IR, SEM and TPR, and investigated as catalyst for wet air oxidation of phenol in a batch reactor at 150 °C. The iron impurity, mainly presented as highly dispersed hematite, acted as active centers and showed good performance without significant iron leaching. The catalyst can be also used as adsorbent to remove leached iron in solution.     

湿式氧化-催化湿式氧化联用处理定影废水

采用湿式氧化(WAO)-催化湿式氧化(CWAO)两段工艺处理定影废水,重点考察了反应时间、温度、压力、pH等因素对WAO处理效果的影响,并进行了CWAO处理WAO出水氨氮的尝试,取得了较好的效果.实验确定WAO适宜的反应条件:温度为160℃、氧分压为1 MPa、反应时间为2 h、进水pH为4.8.该条件下的CODCr去除率达79%,出水pH为1.4.CWAO处理WAO出水时所选定的反应条件:pH为12.9、温度为250℃、氧分压为3 MPa、反应时间为2 h.采用CWAO和WAO联用的方法处理定影废水,CODCr去除率达99.8%,氨氮去除率达97.8%,pH为5.6.     

催化湿式氧化山梨酸生产废水催化剂的研究

以过渡金属氧化物CuO为主活性组分通过对Cr2O3的复合和掺入电子助剂La2O3的考察,研制出适用于催化湿式氧化处理山梨酸生产废水的复合催化剂。考察了各组分浸渍液浓度、焙烧温度和焙烧时间等制备条件对催化剂的催化活性和稳定性的影响,确定了最佳制备条件。结果表明:优化制备的CuO-Cr2O3-La2O3/TiO2催化剂,用于处理山梨酸生产废水时具有良好的催化活性和稳定性,在θ=220℃,p(O2)=2.5 MPa,反应时间t=120 min,山梨酸生产废水初始CODCr=10 030 mg/L条件下CODCr去除率达到96.6%,而在相同条件下未加催化剂的湿式氧化CODCr去除率只有60.8%。     

Carbon supported platinum catalysts for catalytic wet air oxidation of refractory carboxylic acids

Carbon supported platinum (1% wt) catalysts were prepared by the incipient wetness impregnation method and by organometallic chemical vapor deposition. Catalyst characterization was carried out by means of adsorption and thermogravimetric techniques, and by electron microscopy. The catalyst with higher metal dispersion was produced by incipient wetness impregnation. The catalysts were tested in the catalytic wet air oxidation (200°C and 6.9 bar of oxygen partial pressure) of aqueous solutions containing low molecular weight (C₂ to C₄) carboxylic acids. Significant conversions (greater than 60% over 2 h) and 100% selectivity towards water and non-carboxylic acid products were observed for both systems. The initial reaction rate was used to compare the performance of the two catalytic materials and direct correspondence to the metal dispersion was found. No metal leaching was observed during reaction and no significant deactivation occurred in three successive catalytic oxidation runs. A kinetic model based on the Langmuir–Hinshelwood formulation was applied and the results were analyzed in terms of a heterogeneously catalyzed free radical mechanism.     

Catalytic wet air oxidation of butyric acid solutions using carbon-supported iridium catalysts

Aqueous solutions of butyric acid were treated by catalytic wet air oxidation using carbon-supported iridium catalysts in a stirred reactor. Under the operating conditions of 6.9 bar of oxygen partial pressure and 200 °C of temperature, conversions up to 52.9% after 2 h were obtained depending on the type of catalyst used. The effects of butyric acid initial concentration, loading of catalyst, oxygen partial pressure and temperature were investigated and the empirical rate law for acid conversion is presented. Oxidation intermediates such as propionic and acetic acid were identified. The heterogeneous catalyzed free-radical oxidation of butyric acid is discussed.     

Catalytic wet air oxidation of carboxylic acids at atmospheric pressure

Catalytic wet air oxidation of carboxylic acids (maleic acid, oxalic acid and formic acid) was carried out in a batch reactor operated at 160 psi or atmospheric pressure. Pt/Al₂O₃ and the sulfonated poly(styrene-co-divinylbenzene) resin were used as catalysts. Maleic acid was proved to be a refractory substance which could not be oxidized on the Pt/Al₂O₃ catalyst at all atmoshperic pressure, and needed high pressure and high temperature operation for its oxidation. On the contrary, oxalic acid and formic acid were readily oxidized into carbon dioxide and water at 353 K and atmospheric pressure. The pathways of maleic acid oxidation were proposed, and the conversion of maleic acid into oxalic acid was the rate-determining step. When the sulfonated resin catalyst was present together with the Pt/Al₂O₃ catalyst, maleic acid could be oxidized at 353 K and atmospheric pressure. The sulfonated resin catalyst was suggested to hydrolyze maleic acid into readily oxidizable compounds.     

催化湿式氧化高浓度十二烷基苯磺酸钠废水催化剂的研究

以过渡金属氧化物CuO为主活性组分通过对Co3O4的复合和掺入电子助剂CeO2的考察,研制出适用于催化湿式氧化处理高浓度十二烷基苯磺酸钠(SDBS)废水的复合催化剂。考察了各组分浸渍液浓度、焙烧温度和焙烧时间等制备条件对催化剂的催化活性和稳定性的影响,确定了最佳制备条件。结果表明制备的催化剂在合适的条件使CODCr去除率达到88.4%。     

催化湿式氧化处理头孢氨苄废水

采用催化湿式氧化处理头孢氨苄废水,考察反应温度、进水pH及Cl-含量对RCT催化剂性能的影响,并对液体样品及催化剂进行了HPLC、TOC/TN、GC-MS、N2物理吸附-脱附及XRF表征。通过正交实验,得出最佳的工艺条件为:进水pH=4.8,Cl-浓度1 500 mg·L-1,反应温度260℃;对催化剂进行300 h连续寿命考察,废水TOC及TN去除率均超过90%,催化剂稳定性高,活性组分流失较少;废水经催化湿式氧化处理,水中残留的主要有机物均可生化降解。     

Design composite oxide supported Pt catalyst for catalytic wet air oxidation of ammonia with a high concentration in chloride system

Massive discharge of ammonia nitrogen wastewater not only causes eutrophication of the water body but also has a toxic effect on humans and living things. How to deal with ammonia nitrogen wastewater is a crucial topic for researchers. Here, a novel catalyst of Pt@Ti–Si where platinum was supported on a composite oxide of titanium oxide (TiO₂) and silicon oxide (SiO₂) via a one-pot method was successfully synthesized for catalytic wet air oxidation (CWAO) of ammonia with a high concentration (more than 2000 ppm). Due to the improved specific surface area of SiO₂ and the excellent acid-base resistance of TiO₂, the prepared composite oxide-supported platinum catalyst has excellent catalytic performance and good stability for CWAO with a high concentration of ammonia. At 200 °C and the O₂ pressure of 2 MPa for 2 h, the 1%Pt@Ti10–Si1 catalyst has a 96.32% conversion of 2470 ppm ammonia and 97.15% selectivity to N₂ and has good catalytic performance even after five cycles. Under the same reaction conditions, when the chloride concentration in the system is 3000–10000 ppm, the CWAO reaction can be inhibited at an early stage and promote conversion and selectivity at a later stage. The results show that the catalyst has good tolerance to chloride ions, and the treated ammonia nitrogen wastewater can be used for subsequent biochemical processes. Therefore, the developed novel catalyst in this study is effective for the CWAO of highly concentrated ammonia and has potential industrial application value.     

CO and H2 oxidation on a platinum monolith diesel oxidation catalyst

This paper presents experimental and modelling results for the oxidation of mixtures of hydrogen and carbon monoxide in a lean atmosphere. Transient light-off experiments over a platinum catalyst (80 g/ft³ loading) supported on a washcoated ceramic monolith were performed with a slow inlet temperature ramp. Results for CO alone agree with earlier results that predict self-inhibition of CO; that is an increasing light-off temperature with increasing CO concentration. Addition of hydrogen to the feed causes a reduction in light-off temperature for all concentrations of CO studied. The most significant shift in light-off temperature occurs with the addition of small amounts of hydrogen (500 ppm, v/v) with only minor marginal enhancement occurring at higher hydrogen concentrations. Hydrogen alone in a lean atmosphere will oxidise at room temperature. In mixtures of hydrogen and CO, the CO was observed to react first until a conversion of about 50% was observed, at which point the conversion of hydrogen rapidly went from 0 to 100%.

Simulations performed using literature mechanistic models for the oxidation of these mixtures predicted that hydrogen ignites first, followed by CO, a direct contradiction of the experimental evidence. Upon changing the activation energy between adsorbed hydrogen and oxygen, the CO was observed to oxidise first, however, no enhancement of light-off was predicted. The effect cannot be explained by the mechanistic model currently under discussion.     

Wet air oxidation of phenol using active carbon as catalyst

Catalytic wet air oxidation is a promising alternative for the treatment of phenolic waste water which cannot be treated in conventional sewage plants. Catalytic wet air oxidation of an aqueous phenol solution was conducted in a fixed bed reactor operating in trickle flow regime. Either active carbon or a commercial copper oxide supported over γ-alumina was used as catalyst. The performance of both materials was compared in terms of phenol conversion in 240 h tests. The results showed that the active carbon, without any active metal supported, gives the highest phenol conversion. The supported copper catalyst undergoes a rapid deactivation due to the dissolution of the metal active species in the acidic medium in which the reaction takes place. On the other hand, the active carbon maintains a higher activity throughout the test, although a decrease of the phenol conversion was also observed due to both the loss of active carbon by combustion and the reduction of its surface area. The phenol oxidation was proved to occur through a first order mechanism with respect to phenol. After the ten-day run, the catalytic activity of the active carbon was found to be about eight times higher than that of the commercial catalyst, also showing high selectivity to the production of carbon dioxide.     

湿式催化氧化/膜过滤组合工艺膜过滤机理

采用湿式催化氧化/膜过滤组合工艺,以Mo-Zn-Al-O粉末作为催化剂降解阳离子红GTL模拟染料废水,探讨在膜过滤过程中平均孔径为0.1 μm的微滤和0.022 μm的超滤聚偏氟乙烯(PVDF)中空纤维膜的过滤机理。实验结果表明,两种膜过滤组合工艺对染料的降解效果均优于单独湿式催化氧化,0.01 MPa恒压条件下运行120 min后微滤和超滤的膜通量分别衰减了26.63%和16.48%,其原因是粉末催化剂可在微滤膜孔内部沉积形成中间阻塞过滤,后在表面形成滤饼层;而在超滤膜表面仅形成滤饼层。通过实验结果对膜阻力进行计算,可知在相同反应过程后微滤膜产生的不可逆阻力大于超滤膜。在不同反应条件下,催化剂的沉积量与膜阻力呈现线性相关。     

Catalytic oxidation of maleic and oxalic acids under potential control of platinum catalysts

The oxidation of maleic and oxalic acids in diluted aqueous solutions and with platinum catalysts under potential control was studied with the purpose of defining the influence of potential on the catalytic activity. This control was achieved either by an external device or was spontaneously established in the presence of the reactants. The effect of the composition and of the pH was also investigated.

Oxalic acid can be oxidized in mild experimental conditions (T=333 K, P_O2≤1 bar) and at potential values of the catalyst comprised between 0.7<E<1.8 V/RHE with a maximum catalytic activity at 1.3 V/RHE. The catalytic oxidation of this compound under external control of catalyst potential occurs following the same mechanism as the electrocatalytic oxidation. Oxalic acid is weakly adsorbed and its oxidation is inhibited by strongly adsorbed anions.

Maleic acid needs more severe experimental condition to be oxidized (T=383 K, P_O2=1–5 bars) and catalyst potentials in the range of 0.4≤E<1.1 V/RHE. In the same potential range an active adsorbed species was detected.

The catalytic oxidation of maleic acid follows the same mechanism with and without external control of catalyst potential which should be different from the mechanism of the electrocatalytic oxidation.