A study of the ageing and deactivation phenomena occurring during operation of an iron molybdate catalyst in formaldehyde production

Catalyst from a Perstorp Formox formaldehyde plant, operating with high inlet concentration of methanol (10.2 vol.%), was discharged from single tubes of a multi-tube reactor after half the expected lifetime of the catalyst and again after termination of the load. Each tube was filled with two different layers of catalyst. From the inlet of the reactor the first layer was a catalyst mixed with inert rings, which was followed by a second layer of pure catalyst extending from the middle to the outlet of the reactor. Catalyst fractions from the two layers were characterized with various techniques including BET, Fourier transform Raman (FT-Raman) spectroscopy, X-ray diffraction (XRD), elemental analysis with atomic absorption spectroscopy (AAS) and activity measurements. It was found that the surface area of the catalyst in the mixed layer increases during operation while a small decrease is noticeable for the catalyst below in the pure layer. Elemental analysis, XRD and FT-Raman show that during operation of the catalyst there is migration of Mo species from the upper part of the reactor towards the outlet. Activity measurements reveal severe deactivation of the catalyst in the mixed layer. It is concluded that the deactivation primarily is due to formation of volatile species formed by the MoO₃ surface reacting methanol, causing a decrease of the MoO₃/Fe₂(MoO₄)₃ mole ratio in the catalyst. Concerning the catalyst in the pure layer, the condensation of needle-like crystals of MoO₃ mainly occurs on the external surface of the catalyst ring.     

Methanol Selective Oxidation to Formaldehyde over Iron-Molybdate Catalysts

This review deals with the important industrial reaction of formaldehyde manufacture by methanol oxidation over iron molybdate catalysts. Detailed reference is made to the used catalyst, preparation techniques (coprecipitation, sol-gel like, mechanical mixing, etc.) including unsupported and supported catalysts, promoters and characterization methods. The controversial active phase assignment (stoichiometric versus Mo rich iron molybdate) is discussed. The proposed reaction mechanisms and kinetic laws for the main and side reactions are examined. The catalyst deactivation processes are reviewed and the role of Mo excess on these processes is underlined. Finally conclusions and perspectives are presented.     

大型甲醇合成反应器工况的数值分析

年产40万吨甲醇合成反应器由两个绝热-管壳复合型反应器并联组成,并共用一个汽包.以CO、CO2加氢合成甲醇的两个平行反应为独立反应,CO和CO2为关键组分建立一维拟均相数学模型,用龙格-库塔法求解,获得催化床内各组分的摩尔分率和床层温度随轴向的分布.针对以天然气为原料的甲醇生产装置,模拟计算了各操作参数,如沸腾水压力和温度、操作压力,对反应器性能的影响,讨论了催化剂不同时期的反应器操作条件.此模型计算预测值与实际生产数据吻合良好.     

Synthesis of Dimethyl Carbonate from Methyl Carbamate and Methanol Using a Fixed‐Bed Reactor

Several mixed oxide catalysts were prepared by coprecipitation for dimethyl carbonate (DMC) synthesis from methyl carbamate and methanol. During the batch process, the DMC yield was below 35 %. In order to minimize the unfavorable thermodynamic equilibrium and side reactions for the DMC synthesis, a fixed‐bed reactor was designed. A maximum DMC yield of ～ 73 % could be realized over a ZnO‐Al₂O₃ catalyst. The effects of reaction conditions for this type of reactor were investigated in detail.     

Effects of iron precursors on the structure and catalytic performance of iron molybdate prepared by mechanochemical route for methanol to formaldehyde

Mechanochemical synthesis has been applied for many novel material preparations and gained more and more attention due to green and high-efficiency recently. In order to explore the influences of iron precursors on structure and performance of iron molybdate catalyst prepared by mechanochemical route, three typical and cheap iron precursors have been used in preparation of iron molybdate catalyst. Many characterization methods have been employed to obtain the physical and chemical properties of iron molybdate catalyst. Results indicate that iron precursors have the significant impact on the phase composition, crystal morphology and catalytic performance in the conversion of methanol to formaldehyde. It is hard to regulate the phase composition by changing Mo/Fe mole ratios for Fe_2(SO_4)_3 as iron precursor. In addition, as for Fe_2(SO_4)_3, the formaldehyde yield is lower than that from iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O due to the reduction in Fe_2(MoO_4)_3 phase as active phase. Based on mechanochemical and coprecipitation method, the solvent water could be a key factor for the formation of MoO_3 and Fe_2(MoO_4) for FeCl_3·6H_2O and Fe_2(SO_4)_3 as precursors. Iron molybdate catalyst prepared with Fe(NO_3)_3·9H_2O by mechanochemical route, shows the best methanol conversion and formaldehyde yield in this reaction.     

Kinetics of Methanol Oxidation on Supported and Unsupported Pt/Ru Catalysts Bonded to PEM

The kinetics and mechanism of methanol adsorption and oxidation on real Pt/Ru (1:1) electrodes were investigated. In model electrode systems, the addition of supporting proton-conducting electrolyte is necessary. Therefore, the influence of sulphuric acid on the kinetics of methanol adsorption and oxidation was also investigated. It turns out that the steady state adsorption is not significantly affected by the addition of sulphuric acid. However, if sulphuric acid is used as an additional electrolyte, the rate of methanol adsorption and steady state oxidation decreases, whereas the active surface of the catalyst increases. The mechanism of methanol oxidation is not affected by the addition of sulphuric acid. At low potentials, the adsorption of methanol is found to be much faster than its oxidation. Hence, the oxidation of the methanol intermediate species is believed to be the rate-determining step under these conditions. This result is confirmed by apparent orders of reaction of about 0.5. At potentials in the range of 0.3–0.5 V, a mixed activation-adsorption control is supposed, whereas at potentials more positive than 0.5 V, the adsorption of methanol is probably the rds. This is supported by the apparent reaction orders and apparent activation energies of methanol oxidation.     

碱性条件下甲醇阳极氧化碳载催化剂的性能

用化学还原法制备了碳载镍、银、金三种金属单质催化剂,并研究其对甲醇电催化氧化的活性.用X射线衍射光谱(XRD)、X光电子能谱(XPS)表征催化剂的晶相结构、表面组成及价态形式.XRD测试表明均得到了纯度较高的金属单质,催化剂粒径大小在5～11 nm之间,颗粒分布均匀.用循环伏安法测定了不同催化剂对甲醇的电催化氧化的活性...     

甲醇氧化羟化合成碳酸二甲酯

利用氮肥厂生产的甲醇和ＣＯ,以Ｃｕ－Ｐｄ复合催化剂体系催化氧化生产碳酸二甲酯,产品的收率达６０％以上     

Modeling of a Methanol Synthesis Reactor for Storage of Renewable Energy and Conversion of CO2 – Comparison of Two Kinetic Models

The storage of renewable energy over a long time period, via methanol synthesis, will become very important to reach a greenhouse gas‐free energy supply. A steady‐state methanol synthesis flowsheet, containing a 2D pseudo‐homogeneous reactor, flash, and recycle, is modeled in MATLAB. With the kinetic models of Graaf and Bussche & Froment, two frequently used kinetic models for conventional methanol synthesis are compared and evaluated for applicability regarding methanol synthesis from CO₂/H₂. The results are presented for different cases of synthesis gas compositions. Both kinetic models produce similar results when the system is limited by thermodynamic equilibrium. However, differences in reaction rates are observable from the reactor axial molar component profiles of the reaction products.     

Ni-Cr-Co氧化物纳米催化剂对甲醇阳极氧化的电催化性能研究

采用了热分解法合成Ni-Cr-Co氧化物纳米粒子,并用作直接甲醇燃料电池(DMFC)的阳极电催化剂。通过X射线衍射(XRD)、透射电子显微镜(TEM)和扫描电子显微镜(SEM)对催化剂进行表征,制得的纳米催化剂均匀分散,且粒径为25~50 nm。利用循环伏安法(CV)对不同金属摩尔比和焙烧温度下的催化剂在甲醇氧化反应中的活性进行了研究。结果表明,Ni-Cr-Co(摩尔比为1∶1∶1.5)的纳米氧化物对甲醇氧化反应的起始电位、峰值氧化电流密度和If/Ib分别为0.38 V,19.3 mA/cm2和1.72,表现了很好的电催化性能。     

甲烷部分催化氧化合成甲醇和甲醛

本文综述了由甲烷部分催化氧化制甲醇和甲醛研究中所用催化剂的制备条件及催化反应条件,并对用于该反应的催化剂开发和最佳合成工艺条件的选择指出了方向。     

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M < FBR < PBMR-O.     

Influence of Particle Size and Single‐Tube Diameter on Thermal Behavior of Fischer‐Tropsch Reactors. Part II. Eggshell Catalysts and Optimal Reactor Performance

The optimal combination of particle and tube size for simulation of a single tube of a wall‐cooled multitubular Fischer‐Tropsch (FT) reactor with cobalt as catalyst was determined. The maximum size of the tubes, realized without temperature runaway, enhances with increasing particle size until an optimal value is reached, thereby improving the production rate of liquid fuels per tube. Reasons for this are that heat transfer to the cooled tube wall for a given tube size is considerably enhanced by increasing the particle size and that the influence of pore diffusion on the effective rate of FT synthesis gets stronger with rising particle size, which reduces the temperature sensitivity of the reactor and decreases the danger of a temperature runaway. The simulations indicate that the use of FT eggshell catalysts is not an option for fixed‐bed reactors. The temperature sensitivity of the reactor is strongly enhanced, which decreases the maximum tube size and with that the productivity per tube. All these effects are valid in general for wall‐cooled fixed‐bed reactors. Respective criteria are presented.     

Catalytic Oxidation of Methanol to Formaldehyde in a Continuous Fluidized‐Bed Reactor

Partial oxidation of methanol to formaldehyde by using a mixture of ferric and molybdenum oxides as the reaction catalyst at 280–330 °C has been studied in a continuous fluidized bed reactor. The reactor was a cylindrical tube of 20 mm in i.d. and 36 mm in o.d. placed vertically and connected to a truncated coneshaped cyclone separator. The catalyst was prepared by the precipitation method using aqueous solutions of ammonium heptamolybdate and ferric nitrate. The effect of certain parameters, such as temperature, superficial gas velocity and feed flow rates, on the extent of oxidation reaction has been investigated. The maximum size of the catalyst particles was 990 μm, therefore, neither external nor internal diffusion was expected to be effective in the process. The experimental data were correlated with three classes of hydrodynamic models presented for fluidized systems. The best correlation was obtained with compartment type models.     

Fe-5A催化亚甲基蓝溶液湿式H2O2氧化

以九水硝酸铁[Fe(NO3)3?9H2O]和柱状5A分子筛为原料采用湿法浸渍法制备Fe?5A催化剂,催化湿式H2O2氧化亚甲基蓝溶液,考察了间歇反应器中pH值和温度对亚甲基蓝转化率的影响及在连续固定床反应器中床层催化剂装填量、进料液流量、温度和亚甲基蓝入口浓度对亚甲基蓝降解性能的影响. 结果表明,在间歇反应中,在亚甲基蓝浓度50 mg/L、温度70℃、pH为2、反应20 min的条件下,亚甲基蓝的转化率为95.9%. 固定床反应中,随温度降低及进料液流量增加,亚甲基蓝转化率降低;随亚甲基蓝入口浓度增加,亚甲基蓝和化学需氧量(COD)的转化率变化幅度很小. 在温度70℃及pH=2、进料液流量4 mL/min、Fe?5A催化剂装填量1.25 g、亚甲基蓝浓度50?300 mg/L、固定床连续运转5 h的条件下,亚甲基蓝的转化率超过98%,COD转化率大于82%,铁浸出浓度低于3.5 mg/L,相同条件下,装填2.5 g 5A分子筛的固定床中50 mg/L亚甲基蓝的转化率仅为73.3%.     

Modeling of Multi‐Tubular Reactors for Fischer‐Tropsch Synthesis

The results of the simulation of multi‐tubular Fischer‐Tropsch reactors based on a two‐dimensional pseudo‐homogeneous model are presented. The model takes into account the intrinsic kinetics of two commercial iron and cobalt catalysts, intraparticle mass transfer limitations, and the radial heat transfer within the fixed bed and to the cooling medium (boiling water). The effective rate with Co is slightly higher than with Fe. Hence, a temperature level can be used for Co that is 20 °C lower compared to Fe. The conversion and product selectivies are then almost the same and the reactor can be operated safely without a temperature runaway. The results of the simulations are consistent with literature data and show that there is still room for improvement of fixed bed FT reactors, e.g., by an enhanced heat transfer.     

Contrasting the Behaviour of MoO3 and MoO2 for the Oxidation of Methanol

The oxidation of methanol has been measured on MoO₃ and MoO₂. The properties of these two materials are interchangeable, depending upon the conditions in which the reaction is run. MoO₃ produces high yields of formaldehyde, but MoO₂ does not, due to the importance of the Mo⁶⁺ state for the selective reaction. However, if the MoO₃ material is run in anaerobic conditions it behaves in a very similar way to MoO₂, due to the presence of Mo⁴⁺ in the surface layers. In complement to this MoO₂ converts to high yield behaviour when run in aerobic conditions, due to the conversion of the material to Mo⁶⁺ at the surface, and, ultimately to MoO₃ in the bulk. In TPD experiments MoO₃ yields formaldehyde, whereas MoO₂ yields CO. In both materials oxygen transport within the lattice becomes appreciable above 300 °C, and the reaction proceeds via the Mars-van Krevelen mechanism.     

Performance of catalytic reactors for the hydrogenation of CO2 to hydrocarbons

Fluidized bed and slurry reactors were employed to increase the CO₂ conversion and desirable product selectivity in the direct hydrogenation of CO₂ to hydrocarbons over K-promoted iron catalysts, as it is beneficial for the removal of heat generated due to highly exothermic nature of the reaction. The iron catalysts (Fe-K/Al₂O₃ and Fe-Cu-Al-K) were characterized by BET surface area, CO₂ and H₂ chemisorption, temperature-programmed reduction (TPR), X-ray diffraction (XRD) and temperature-programmed hydrogenation (TPH). The results of TPR and TPH study clearly indicated that co-precipitated Fe-Cu-Al-K catalyst has much higher reducibility and catalytic activity of CO₂ hydrogenation at low temperature than Fe-K/Al₂O₃. The performance of fluidized bed or slurry reactors was superior to that of fixed bed reactor for the CO₂ hydrogenation over Fe-Cu-Al-K catalyst in terms of CO₂ conversion and hydrocarbon productivity. Moreover, light olefins and heavy hydrocarbons were selectively synthesized in fluidized bed and slurry reactors, respectively. The optimum operation conditions and the effects of operating variables on the CO₂ conversion and its product distribution in these catalytic reactors were also discussed.     

载体对Au-Pd催化剂甲醇部分氧化制氢性能的影响

用PVP保护乙醇还原法制备了一系列Au-Pd/MOx(M=Zn、Ce、Fe、Ti、Cr和Al)双金属催化剂,考察了不同载体对Au-Pd催化剂甲醇部分氧化制氢性能的影响,用XRD、TG、TPD、TPR和TPH等对催化剂进行了表征。结果表明,载体对催化剂性能有较大影响,与钛、铬和铝氧化物载体相比,448K时偏碱性的锌、铈和铁氧化物载体负载的Au-Pd催化剂的甲醇转化率均在80.0%以上,催化剂积碳量降低。其中以Au-Pd/ZnO催化剂的效果最好,523K时甲醇转化率和氢气选择性分别为99.0%和45.6%,反应20h后积碳量仅为0.0232g/gcat.。     

Kinetics of Sulfite Oxidation in the Simultaneous Desulfurization and Denitrification of the Oxidation‐Absorption Process

The kinetics of sulfite oxidation in the simultaneous desulfurization and denitrification of the oxidation‐absorption process was investigated with a bubbling apparatus under the conditions of varying pH, sulfite concentration, nitrite concentration, temperature, and air flow. The results indicate that the oxidation of sulfite is promoted dramatically by mixing with nitrite, due to the decline of the apparent energy of activation and the initiation of nitric dioxide decomposition by nitrite. An increase of the nitrite concentration, the air flow, the reaction temperature, or the pH supports the decomposition of nitrite and the production of nitric dioxide, thus leading to an enhancement of the sulfite oxidation rate. A kinetic model is established according to the experimental results. A satisfactory agreement between the calculated and the experimental values is obtained.