Hydrogenation/hydrogenolysis of disulfides using sulfided Ni/Mo catalysts

The mechanism of the hydrogenation/hydrogenolysis of dinitrodiphenyldisulfides using sulfided NiMo/γAl₂O₃ catalysts has been examined in detail. Although two routes are possible, the major pathway involves an initial SS bond cleavage followed by reduction of the nitro group. Importantly, the disulfide hydrogenolysis occurs in the absence of the catalyst with the role of the catalyst thought to be to activate the hydrogen and trap the cleaved intermediate as well as facilitate the reduction of the nitro group. Monitoring the mass balance throughout the reaction demonstrates the difficulty in measuring intrinsic kinetics for gas–liquid–solid reactions. Although the mass balance is restored at the end of the reaction, up to 45% of the substrate/products is found to be adsorbed on the catalyst during the reaction.     

影响Claus尾气加氢催化剂性能的动力学研究

实验室通过对低温Claus尾气加氢催化剂动力学研究,考察了Claus尾气含硫化合物加氢反应的规律。通过对影响Claus尾气加氢催化剂性能的主要因素分析,阐述了过程气中烃类反应导致的催化剂积炭速率与烃含量、催化剂使用温度、催化剂运转时间的关系;通过使用XRD、SEM等技术手段,对热老化前后Claus尾气加氢催化剂晶相、金属分散、孔结构等性质进行测试和表征。从不同角度研究、探讨影响催化剂性能的因素,对于低温Claus尾气加氢催化剂及其配套工艺的开发和应用具有指导意义。     

Activity monitoring of Claus catalysts in sulfur recovery units

Methodical principles of catalyst activity monitoring in Claus reactors based on the determination of the rate constant of the reaction of hydrogen sulfide conversion at catalyst temperatures lower than 280°C are discussed. The procedure is justified by data from laboratory experiments (in the range of concentrations [H₂S]₀ = 1.5–7 vol %), pilot tests ([H₂S]₀ = 0.8–37.4 vol %) of an alumina-based catalyst AO-NKZ-2 produced by ZAO Novomichurinsk Catalyst Plant, and by the results of its test in the Claus reactor of the department for coke oven gas purification of by-product-coke plant at the OAO Magnitogorsk Integrated Iron-and-Steel Works. The procedure is recommended for reliable monitoring of the current activity and estimation of the residual life of catalysts in the Claus industrial reactors operating under conditions of substantial variations in the composition of the process gas, as well as for comparative estimates of catalyst activity in the Claus process.     

Sulphur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas II. Chemisorption of hydrogen sulphide

The effect of different components of gasification gas on sulphur poisoning of nickel catalysts were studied. In addition, the sulphur distribution and content of nickel catalyst beds were analysed to account the poisoning effect of sulphur on the activity of catalysts to decompose tar, ammonia and methane. The desorption behaviour of chemisorbed sulphur from the bed materials was monitored by temperature programmed hydrogenation (TPH). It was established that bulk nickel sulphide was active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The decomposing activity of methane was not affected by bulk nickel sulphide formation, but that of toluene was decreased. The activity of the catalyst regained rapidly when H₂S was removed from the gas. However, the conversion of ammonia was not regained at as high a level as before sulphur addition, most probably due to irreversible sulphur adsorption on the catalyst. The temperature increase could also be used to regenerate the catalyst performance especially in respect to methane and toluene. Sulphur adsorbed on nickel catalysts in different chemical states depends on the process conditions applied. At >900°C the sulphur adsorbed on the catalyst formed an irreversible monolayer on the catalyst surfaces, while at <900°C the adsorbed sulphur, probably composed of polysulphides (multilayer sulphur), was desorbed from the catalyst in sulphur-free hydrogen containing atmosphere. However, a monolayer of sulphur still remained on the catalyst after desorption. The enhanced effect of high total pressure on sulphur-poisoning of nickel catalysts could be accounted for the increased amount of sulphur, probably as a mode of polysulphides, adsorbed on the catalyst.     

掺海泡石原位晶化催化裂化催化剂的研究

用海泡石和高岭土混合物为原料,以原位晶化技术制备催化裂化(FCC)催化剂,考察了海泡石对结晶度、硅铝比和抗钒性能的影响。结果表明掺海泡石的原位晶化产物与未加海泡石相比,结晶度较低,硅铝比较高,海泡石含量在5%~30%范围时,结晶度和硅铝比变化不大。该催化剂水热活性(100%水蒸汽、800℃、17h)较未加海泡石低,但钒污染(质量分数5×10-3)后活性保留率却高出25%,抗钒能力较高。     

超级克劳斯装置的工艺和控制

介绍了超级克劳斯装置的工艺特点,阐述了燃烧炉控制系统和氧化空气控制系统的设计意图,将该装置与常规克劳斯工艺进行了比较。结果表明,超级克劳斯装置硫回收率超过99.5％;从化学反应的根本上实现了对催化剂活性的保护和对SO2、H2S的抑制。     

Activation of off site presulfided Cobalt---Molybdenum catalysts

An oxidic Co---Mo catalyst presulfided by the SULFICAT® process has been studied by XPS. Results indicate that the strong interaction of the alkylpolysulfide with the solid provokes a partial reduction of both the sulfur and molybdenum ions. Treated under hydrogen, the adsorbed species decompose at temperatures as low as 160–220°C converting the initial Mo⁶⁺species into sulfided Mo⁴⁺. The sulfidation state of the active phase increases with the hydrogen pressure. Comparison with the conventional sulfiding procedure indicates that the SULFICAT® process results in a higher dispersion of the sulfided active phase.     

Improvement of the method of obtaining gas sulfur

An improved method of obtaining gas sulfur using the Claus and Sulfren processes, which provides an increase in its yield to 99.6–99.8%, is suggested. To realize this method, new catalysts are developed, namely, the alumina catalyst for the Claus process, the catalyst for the reduction of SO₂, the catalyst for the Sulfren process, and the low-temperature catalyst for the direct oxidation of H₂S, which provided for the utilization of previously not used components of the gas medium H₂ and CO forming at the thermal stage. This method is recommended for introduction at the enterprises of OAO GAZPROM, Orenburg and Astrakhan, gas processing plants. No substantial changes in the hardware implementation of technological lines will be necessary; it will be sufficient to reconstruct the reactors of the Sulfren process.     

Reaction and characterization studies of an industrial Cr-free iron-based catalyst for high-temperature water gas shift reaction

Activity and stability of an industrial Cr-free iron-based catalyst (NBC-1) for high-temperature water gas shift (WGS) reaction were studied in a fixed-bed reactor under 350 °C, 1 atm, H₂O:gas = 1:1 and 3000 h⁻¹ (dry-gas basis). Physical properties of the NBC-1 catalyst before and after the WGS reaction, the desorption behavior of H₂O, CO, CO₂ and H₂, and surface reaction over the catalyst were characterized by BET, X-ray diffraction (XRD), Mössbauer emission spectroscopy (MES), temperature programmed desorption (TPD) and temperature programmed surface reaction (TPSR). The NBC-1 catalyst is active and has excellent thermo-stability even after pretreatment at a high temperature of 530 °C. Its activity and thermo-stability are comparable to those of an UCI commercial Fe-Cr catalyst, C12-4. XRD and MES studies show that iron in the fresh NBC-1 catalyst is present as γ-Fe₂O₃, most of which is converted to Fe₃O₄ during reduction and reaction. Results of TPD demonstrate that adsorbed CO₂ and CO cannot exist on the NBC-1 surface beyond the temperature of 300 °C while higher temperatures (>400 °C) are required to completely desorb H₂O. A redox mechanism of WGS on the NBC-1 surface is proposed based on the TPD and TPSR observations.     

Development and reactivity tests of Ce-Zr-based Claus catalysts for coal gas cleanup

Claus reaction (2H₂S + SO₂ ↔ 3/nS_n + 2H₂O) was used to clean the gasified coal gas and the reactivity of several metal oxide-based catalysts on Claus reaction was investigated at various operating conditions. In order to convert H₂S contained in the gasified coal gas to elemental sulfur during Claus reaction, the catalysts having the high activity under the highly reducing condition with the moisture should be developed. CeO₂, ZrO₂, and Ce_1−xZr_xO₂ catalysts were prepared for Claus reaction and their reactivity changes due to the existence of the reducing gases and H₂O in the fuel gas was investigated in this study. The Ce-based catalysts shows that their activity was deteriorated by the reduction of the catalyst due to the reducing gases at higher than 220 °C. Meanwhile, the effect of the reducing gases on the catalytic activity was not considerable at low temperature. The activities of all three catalysts were degraded on the condition that the moisture existed in the test gas. Specifically, the Ce-based catalysts were remarkably deactivated by their sulfation. The Ce-Zr-based catalyst had a high catalytic activity when the reducing gases and the moisture co-existed in the simulated fuel gas. The deactivation of the Ce-Zr-based catalyst was not observed in this study. The lattice oxygen of the Ce-based catalyst was used for the oxidation of H₂S and the lattice oxygen vacancy on the catalyst was contributed to the reduction of SO₂. ZrO₂ added to the Ce-Zr-based catalyst improved the redox properties of the catalyst in Claus reaction by increasing the mobility of the lattice oxygen of CeO₂.     

RCTI工艺——克劳斯尾气装置性能新标准

WorleyParsons公司开发了一种新的克劳斯尾气处理新工艺--RCTI工艺,作为其它尾气处理工艺的替代技术.在RCTI工艺中克劳斯尾气由高压蒸汽或导热油间接加热,然后依次在加氢催化剂、选择性氧化催化剂(如Selectox TM)上进行低温还原及低温H2S氧化,尾气最后放空.由于无需设置还原气发生器,RCTI工艺免除了天然气消耗并且减少了CO2排放,如有必要,所产生的SO2可利用非可再生苛性碱液或可再生溶剂捕集.在比较RCTI工艺及常规工艺的基础上论述了克劳斯尾气处理工艺的选择标准.     

Low temperature SCR of NO with NH3 over carbon nanotubes supported vanadium oxides

A novel multiwalled carbon nanotube (CNTs) supported vanadium catalyst was prepared. The structure of catalyst prepared was characterized by TEM, BET, FTIR, XRD and temperature-programmed desorption (TPD) methods. The results indicated that vanadium particles were highly dispersed on the wall of carbon nanotubes. The V₂O₅/CNT catalysts showed good activities in the SCR of NO with a temperature range of 373–523 K. The Lewis acid sites on the surface of V₂O₅/CNT are the active sites for the selective catalytic reduction (SCR) of NO with NH₃ at low temperatures. It was suggested that the reaction path might involve the adsorbed NH₃ species reacted with NO from gaseous phase and as well as the adsorbed NO₂ species. The diameter of CNTs showed positive effect on the activities of the catalysts. Under the reaction conditions of 463 K, 0.1 Mpa, NH₃/NO = 1, GHSV = 35,000 h⁻¹, and V₂O₅ loading of 2.35 wt%, the outer diameter of CNTs of 60–100 nm, the NO conversion was 92%.     

A study on the reactivity of Ce-based Claus catalysts and the mechanism of its catalysis for removal of H2S contained in coal gas

In this study, Claus reaction was applied for the selective removal of H₂S contained in the gasified coal gas, and the characteristics of Claus reaction over the Ce-based catalysts were investigated to propose the reaction mechanism. The Ce-based catalysts showed a high activity on Claus reaction. Specially, Ce_0.8Zr_0.2O₂ catalyst had a higher activity than CeO. On the basis of our experimental results, it was proposed that the selective oxidation of H₂S was carried out by the lattice oxygen in the Ce-based catalysts and that the reduction of SO₂ was performed by the lattice oxygen vacancy in the reduced catalyst. Since the mobility of the lattice oxygen in Ce_0.8Zr_0.2O₂ composite catalyst was better than the one in CeO₂, Ce_0.8Zr_0.2O₂ provided more lattice oxygen for the selective oxidation of H₂S. It was presumed that the reaction mechanism to convert H₂S and SO₂ into elemental sulphur over our prepared catalysts was different from the mechanism over the solid-acid catalysts. It is believed that Claus reaction over the Ce-based catalysts was carried out by the redox mechanism. Since the moisture was contained in the major components, CO and H, of the gasified fuel gas, the effects of CO and H₂O on the catalytic reaction were investigated over a Ce-based catalyst. The conversion of H₂S and SO₂ was decreased in Claus reaction over the Ce-based catalysts as the concentration of either H₂O or CO in the gasified coal gas was increased. Under the circumstances of the coexistence of both moisture and CO, however, the conversion was increased as the concentration of CO was increased. The reactivity of Claus reaction was varied in terms of the concentration ratio of CO to H₂O. The maximum conversion of H₂S and SO₂ was achieved in the condition of that the concentration of CO contained in the reacting gas was higher than the one of H₂O. The conversions of H₂S and SO₂ did not match to the stoichiometric ratios of Claus reaction. The higher conversion of H₂S was obtained in the higher concentration of H₂O, while the higher conversion of SO₂ was achieved in the higher concentration of CO. It was another evidence to indicate that the Claus reaction over the Ce-based catalysts was carried out by the redox mechanism.     

NOx选择催化还原用Au/海泡石催化剂的研究

以天然海泡石为原料,对其进行酸改性后作为催化剂载体。采用浸渍法制备了用于CO选择催化还原NOx的负载型Au/海泡石催化剂。设计正交实验对海泡石酸改性条件进行了研究,对催化剂催化还原NOx的活性进行了评价。实验结果表明,该催化剂对于NOx催化还原反应有一定活性。对酸改性前后的海泡石及制得的催化剂进行了TGA、IR和XRD分析,证实海泡石是一种较好的催化剂载体。     

The influences of the gas rate dissolution and mass-transfer limitation at the interfaces on selectivity of gas–liquid processes in stirred reactors with a suspended catalyst

A complex mathematical model accounting for the hydrogen dissolution process in suspensions and mass-transfer steps at the liquid–solid interface for the gas and liquid components is given. The calculated data according to the model for the reaction A→B→C shows, that the yield of an intermediate product B is very much affected by the relation of the gas component mass-transfer coefficient on the gas–liquid interface to that on the liquid–solid one. The hydrogenation of chlornitroaromatic compounds was analysed. The kinetics of the catalytic reduction of p-chlornitrobenzene to p-chloraniline via corresponding arylhydroxilamine on the Ir/C catalyst experimentally in a batch reactor has been studied. In this process the first reactions depend on the hydrogen concentration but the second ones are not dependent — this is a disproportion of the intermediate product to the final product — amine.     

Re-investigating the CO oxidation mechanism over unsupported MnO, Mn2O3 and MnO2 catalysts

Kinetic study of CO oxidation in combination with experiments of temperature-programmed oxidation (TPO) and reduction (TPR) have been performed on various unsupported crystalline manganese oxides (MnO_x); while the reactivity shows an order of MnO ≤ MnO₂ < Mn₂O₃ in a mixture of unit ratio of O₂/CO at/below 523 K. We propose that under the current conditions the interaction of adsorbed CO and O is mainly responsible for CO₂ formation on Mn₂O₃ and MnO₂ catalysts, following either the Langmuir–Hinshelwood mechanism or Eley–Rideal mechanism. Meanwhile, direct evidence from transient CO oxidation suggests that the Mars-van-Krevelen mechanism may occur for all catalysts simultaneously, especially, it is predominant for the MnO catalyst. The evidence of structural modifications during reaction was confirmed by Raman spectra obtained from used MnO.     

Liquid-phase methanol synthesis in apolar (squalane) and polar (tetraethylene glycol dimethylether) solvents

The kinetics of the three-phase methanol synthesis over a commercial Cu–Zn–Al₂O₃ catalyst were studied in an apolar solvent, squalane and a polar solvent, tetraethylene glycol dimethylether (TEGDME). Experimental conditions were varied as follows: P=3.0–5.3 MPa, T=488–533 K and Φ_vG/w=7.5×10⁻³–8×10⁻³ Nm³ s⁻¹kg⁻¹_cat. The nature of the slurry–liquid influences the activation energy and the kinetic rate constant by interaction between adsorbed species and solvent and by competitive adsorption of the solvent on the catalyst surface. The rate of reaction to methanol observed in TEGDME appeared to be about 10 times lower than in squalane. TEGDME reduces the reaction rate, which is a disadvantage for its use as a solvent.     

In situ FTIR study on NO reduction by C3H6 over Pd-based catalysts

The reaction mechanism of the reduction of NO by propene over Pd-based catalysts was studied by FTIR spectroscopy. It was observed that the reaction between NO and propene most probably goes via isocyanate (2256–2230 cm⁻¹), nitrate (1310–1250 cm⁻¹) and acetate (1560 and 1460 cm⁻¹) intermediates formation. Other possible intermediates such as partially oxidized hydrocarbons, NO₂, and formates were also detected. The reaction between nitrates and acetates or carbonates reduced nitrates to N₂ and oxidized carbon compounds to CO₂. In situ DRIFT provides quick and rather easily elucidated data from adsorbed compounds and reaction intermediates on the catalyst surface. The activity experiments were carried out to find out the possible reaction mechanism and furthermore the kinetic equation for NO reduction by propene.     

OXIDATIVE DEHYDROGENATION OF ETHANE OVER A MONOLITH COATED BY MOLYBDENUM-VANADIUM-NIOBIUM MIXED-OXIDE CATALYST

Oxidative dehydrogenation of ethane to ethylene was investigated using Mo 0.71 V 0.21 Nb 0.08 mixed-oxide catalyst, in powder form and coated over a monolith. At 570°C and with a feed stream containing an O 2 /C 2 H 6 mole ratio of one, ethylene selectivity value reaching to 96% was obtained at a conversion level of about 5% with the monolith-supported catalyst. DRIFTS studies indicated the presence of adsorbed ethoxide species. The proposed reaction scheme for the production of ethylene includes the elimination of β-hydrogen of adsorbed species by the lattice oxygen.     

K2CO3/γ-A12O3催化剂在棉籽油制备生物柴油中的应用

利用等体积浸渍法制备K₂CO₃/γ-A1₂O₃负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K₂CO₃/γ-Al₂O₃具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K₂CO₃/γ-A1₂O₃负载型固体碱催化剂经济实惠且催化效果良好。