Effects of organic nitrogen compounds on hydrotreating and hydrocracking reactions

A major issue encountered in hydrotreating and hydrocracking reactions, as in many others fixed bed catalytic processes, is the decrease of catalytic activity with time on stream. The organic nitrogen compounds act as temporary poisons in hydroprocessing catalysts besides being coke precursors. The inhibiting effects of nitrogen compounds present in crude oil have been studied on SRGO hydrotreating reactions and VGO hydrocracking reactions. The results show that selective removal of nitrogen by adsorption using silica and alumina in varying proportions, would not only increase the HDS catalyst activity by more than 60%, but would also reduce hydrogen consumption. This step of nitrogen removal can be installed additionally in the upstream of an existing SRGO HDS reactor to achieve higher desulphurization or can be designed with the grass roots units.

The inhibition effects of nitrogen on VGO hydrocracking have been studied at different temperatures and the reaction has been found to be highly non-linear in nature and the conversion rapidly drops and the slope becomes less steep as the nitrogen level increases. At higher reaction temperature, the drop in activity or conversion with feed nitrogen is less than that in lower temperatures due to the higher rate of desorption of nitrogen compounds at elevated temperatures. The drop in conversion with nitrogen compounds present in VGO indicates the presence of organo nitrogen compounds having higher basicity compared to the nitrogen compounds by pyridine doping. The hysteresis exists in adsorption/desorption of nitrogen compounds and it indicates that desorption is a very slow process. With the increase of nitrogen compounds in the feed, the conversion drops rapidly and it takes long time to reach an equilibrium value. Similarly, with the step increase in reactor temperature, nitrogen desorption takes place at a slow rate and the conversion level comes to an equilibrium value after 8 days.

The observed effects of nitrogen inhibition on SRGO hydrotreating and VGO hydrocracking conversion are explained reasonably well by kinetic models.     

Catalytic wet oxidation of phenol using membrane reactors: A comparative study with slurry-type reactors

The wet air oxidation of phenol over cerium mixed oxides has been carried in autoclave slurry-type reactor and also in a contactor type membrane reactor to assist about the benefits provided by the employment of the mesoporous top layer of a ceramic tubular membrane as catalyst (Ce mixed oxides) support. The effect of mixed oxide composition and use of Pt as dopant onto the phenol removal rate and selectivity towards mineralization have been studied on both types of reactor. For slurry-type reactors, two different autoclave reactors were used: one mechanically stirred highly pressurized, and the other magnetically stirred containing a porous stainless steel membrane as gas diffuser in an attempt to attain higher gas–liquid interfacial area. The performances of these reactors have been compared under similar reaction conditions (i.e. catalyst loading/liquid volume, temperature, phenol concentration) although the way in which reactants are fed to the reaction vessel (different among each other configuration) is clearly affecting the CWO phenol degradation route. From the catalytic systems studied, Pt doped Ce–Zr mixed oxides exhibit the best reaction performance in spite of the achieved phenol conversion levels are below 50%. For autoclave reactors, the gas feeding to the liquid volume by a membrane diffuser has almost no effect on phenol removal for the reaction conditions tested; whereas the catalytic membrane contactor type reactor clearly outperform autoclave reactor provided with membrane diffuser.     

Analysis of a model for a nonisothermal continuous fluidized bed catalytic reactor

A three-phase model, consisting of a dilute or bubble phase, an interstitial gas phase and a solids phase, has been developed for a non-isothermal gas fluidized-bed catalytic reactor with continuous circulation of catalyst particles. The dilute phase is assumed to be in plug flow, the interstitial gas is considered to be either perfectly mixed or in plug flow, and the particles are assumed to be perfectly mixed.It is shown that the conversion in a reactor and steady state temperature and concentration profiles are the same irrespectively of the assumed flow pattern in the interstitial gas.The numerical computations were done for the case of a single irreversible reaction with or without catalyst decay and for the case of two consecutive irreversible reactions. In the case of an adiabatic reactor and ordinary exothermic reactions, or in the case of a cooled reactor with a highly exothermic reaction, multiple steady states may occur.     

Modeling and experimental studies of methyl methacrylate polymerization in a tubular reactor☆

In this study, rheological examination of the mixture of a tubular reactor in which methyl methacrylate was po-lymerized has been studied. The n (flow behavior index) value of Power Law Model of mixture contained in the reactor has been determined within the span of 0.3492 to 0.9889 by curve fitting. Employing these numerical data for velocity profile, the reactor has been modeled. Moreover, the functions of the reactor have been com-pared in the three modes of plug, mixed and laminar flow. The results obtained in this research indicate that the polymethyl methacrylate mixture contained in the reactor is pseudo-plastic. Moreover, as the conversion grows, the velocity profile starts as a parabolic profile and approaches the plug mode;although it never reaches the plug. The other conclusions borne in this study indicate that when the reactor's radius is decreased, the conversion rate grows. However, as decreasing the radius would also reduce the productions rate, this procedure is not economical. Finally, in this modeling, the amount of conversion is equal to 56.47%at the end and according to its laboratory proportion which is 55.88%, it has reached the conclusion that the modeling duly undertaken is applicable and valid.     

Experimental study on the optimum performance of an adiabatic MT reactor

The performance of an adiabatic MT reactor has been studied under various experimental conditions, using the reaction between hydrogen peroxide and sodium thiosulphate. Following the M-section, consisting of a CSTR, the T-section was made up of a large number of small stirred tanks in series. The same general condition for optimizing the MT model, that the reaction rate in the M-section be a maximum, is shown to apply when maximizing the conversion for a given residence time as it was shown previously to apply when minimizing the residence time for a given conversion. Very good agreement is shown between theoretical and experimental results, confirming the superior results often obtained with an MT combination as compared with those given by a stirred tank or a tubular reactor under similar conditions. Bi-stable steady states of conversion have been achieved and their effect shown on the performance of the combined reactor.     

Conversion Enhancement of Equilibrium-Limited Reactions in a Two-Membrane Reactor

Abstract

Analysis of two-membrane reactor performance is carried out on a simple, perfectly mixed reactor model. The influence of the design and operating parameters and physical properties of the system on conversion for equilibrium reactions of the type A ? B + C have been studied. Also, the effects of the presence of inerts at both the reaction and permeation sides of the reactor have been discussed. It has been shown that the two-membrane reactor exhibits superior performance as compared to the single-membrane reactor.     

厌氧氨氧化反应器的启动及其脱氮性能研究

采用添加多层多孔板的升流式厌氧污泥床接种混合污泥,于78 d内成功启动厌氧氨氧化反应器。第75天,反应器对NH4+-N和NO2--N的去除率达95%以上,容积氮去除负荷达0.525 kg/(m3·d)。启动后,快速提高进水基质浓度,反应器出现抑制现象,且抑制前后三氮之比具有显著变化。运行后期,底部出现红棕色污泥。与普通的升流式厌氧污泥床相比,其具有喷动床效应及水利筛分作用,有利于颗粒污泥的形成。     

Etude cinétique de la réaction de carburation du molybdène par le méthane

The kinetics of carburization of molybdenum by methane has been studied in a fluidized bed differential reactor. Scanning electron microphotographs of the reacting solids, at various conversion levels, have been analyzed. It has been shown that pore formation resulted in considerable increase in reaction rate. Initial rates are analyzed in terms of growth of superficial carbide nucleus. The rate of growth of the germs was found to decrease with time of reaction. A model is proposed to explain this decrease.     

Methane Steam Reforming in Hydrogen-permeable Membrane Reactor for Pure Hydrogen Production

Steam reforming of methane over a ruthenium catalyst has been carried out at 500 °C in a membrane reactor equipped with a palladium membrane supported on a porous stainless steel tube. Hydrogen and carbon dioxide are mainly produced in the reaction, while hydrogen is selectively permeated through the membrane. Since equilibrium-shift takes place by hydrogen separation from the reaction mixture, the methane conversion significantly exceeds the equilibrium value, which is low at 500 °C. The selectivity to carbon monoxide by-produced in the reaction is lower than that expected from the equilibrium. Although the equilibrium conversion decreases with an increase in the reaction pressure, the conversion with the membrane reactor can increase because the hydrogen separation is promoted by the pressure increase. The catalytic activity is an important factor to produce a sufficiently high methane conversion and it is enhanced at a high reaction pressure.     

气相三氧化硫磺化甲苯制备对甲苯磺酸——温度对磺化反应的影响

气相三氧化硫磺化甲苯制备对甲苯磺酸——温度对磺化反应的影响刘邦孚吴金川张德立汪宝和谈道（天津大学石油化工技术开发中心，天津３０００７２）关键词：甲苯三氧化硫磺化对甲苯磺酸１前言对甲苯磺酸是制备对甲酚的重要中间体，目前工业上主要是采用浓硫酸磺化甲苯来生...     

Nuclear magnetic resonance imaging of an operating gas–liquid–solid catalytic fixed bed reactor

This work reports our pioneering application of the nuclear magnetic resonance imaging (MRI) technique to the dynamic in situ studies of gas–liquid–solid reactions carried out in a catalytic trickle bed reactor at elevated temperature. The major advance of these studies is that MRI experiments are performed under reactive conditions. We have applied MRI to map the distribution of liquid phase inside a catalyst pellet as well as in a catalyst bed in an operating trickle-bed reactor. In particular, our studies have revealed the existence of the oscillating regimes of the heterogeneous catalytic hydrogenation reaction caused by the oscillations of the catalyst temperature and directly demonstrated the existence of the coupling of mass and heat transport and phase transitions with chemical reaction. The existence of the partially wetted pellets in a catalyst bed which are potentially responsible for the appearance of hot spots in the reactor has been also visualized. The combination of NMR spectroscopy with MRI has been used to visualize the spatial distribution of the reactant-to-product conversion within an operating reactor.     

Kinetics of cupric oxide catalysed oxidation of propylene in a stirred reactor

The catalytic air oxidation of propylene to acrolein over a supported copper oxide catalyst was investigated in a continuous stirred vessel reactor between 375° and 450°C at atmospheric pressure. The effect of temperature, ratio of oxygen to propylene in feed and total feed rate (or contact time) on the conversion of propylene and the yield of acrolein were determined. It was found that with an increase in temperature, ratio of oxygen to propylene and contact time, the yield drops considerably though conversion increases. A study of the mixing characteristics of the stirred vessel reactor was carried out by following the conversion at various stirrer speeds. The kinetic data obtained were tested to determine the most probable model by the Hougen-Watson method. The model that satisfactorily correlated the data describes the rate-controlling step as the surface reaction occurring between adsorbed propylene, a vacant site and oxygen in the gas phase. The following Hougen-Watson type rate equation has been proposed The constants in the rate equation have been expressed as a function of temperature.     

Performance characteristics of a cstr containing immobilised enzyme particles

The effects of internal and external substrate diffusion resistances on the performance of a continuous stirred tank reactor are analysed in this work. Both immobilised enzymatic reactions with and without substrate inhibitions are considered. The substrate conversion for the reaction without substrate inhibition is dependent on four dimensionless parameters: the Thiele modulus, the dimensionless Michaelis constant, the mass transfer Nusselt number and β, which represents a combination of particle hold-up, maximum reaction rate, input substrate concentration and substrate residence time in the continuous stirred tank reactor. For the corresponding reaction with substrate inhibition, the effect of the additional dimensionless inhibition constant on the substrate conversion is also very significant. The substrate conversion generally decreases with decrease in dimensionless parameter β, increase in Thiele modulus and decrease in mass transfer Nusselt number. For the reaction with small Thiele modulus, β and strong substrate diffusion resistances, a multireactor system may be needed if a certain desired substrate conversion is required. The single CSTR model can be extended to describe the multireactor system and the effect of the number of reactors on the substrate conversion for a two- or more reactor system is also examined.     

Experimental study on catalytic steam gasification of natural coke in a fluidized bed

The gasification characteristics of natural coke from Peicheng mine with steam were investigated in a fluidized bed reactor. The effects of catalyst type, composition and dosage of catalyst on the yield, components and heating value of product gas, and carbon conversion rate were examined. The results show that fluidized bed gasification technology is an effective way to gasify natural coke. Also the results indicate that individual addition of K-, Ca-, Fe-, Ni-based catalyst effectively increases the gasification reaction rate of the natural coke samples. With the increase in catalyst dosage, the yield and heating value of product gas per hour increase obviously, and carbon conversion rate is improved substantially. Each of aforementioned catalysts has similar catalytic effect and trend, among which the effect of Ca-based catalyst is a little weaker. The optimum metal atom ratio of mixed catalyst is Fe/Ni/others = 35/55/10, and the mixed catalyst displays maximum catalytic performance when the catalyst dosage in the natural coke is about 4%. The experimental findings provide an interesting reference for large-scale development and utilization of natural coke.     

Operability of an Industrial Methanol Synthesis Reactor with Mixtures of Fresh and Partially Deactivated Catalyst

Disposal of spent catalyst is a common practice in industrial methanol synthesis. However, the spent catalyst has, generally, a good level of activity and can be used if mixed with fresh catalyst. In this work the operation of an industrial methanol synthesis reactor with mixtures of fresh and partially deactivated catalyst was investigated using a one‐dimensional transient model. Analysis of the deactivation behavior of low‐pressure methanol synthesis catalyst shows there is an extremely sharp rate of deactivation in a small part of the catalyst life‐time, which is followed by a relatively slow rate of deactivation in the remaining catalyst cycle‐time. Different configurations were studied for catalyst recycling, and two limiting cases are discussed in detail in this paper, namely layered and homogeneous (mixed) bed models. In the first one, the catalyst was segregated into two alternate layers of fresh and partially deactivated catalyst, while in the second homogeneity of the catalyst bed was simulated by segregating a large number of alternate layers of fresh and partially deactivated catalyst. It was observed in both cases that when catalyst recycling is used, the process does not depart significantly from the standard operating conditions, and also that the mixed bed had less influence on the reactor performance than layered one.     

Synthesis Gas and Zinc Production in a Noncatalytic Packed‐Bed Reactor

A noncatalytic packed‐bed reactor has been constructed for management of the reduction of ZnO by methane, which leads to co‐production of synthesis gas and zinc. The reactor consisted of a simple vertical pipe filled with ZnO pellets. These pellets underwent reaction with a pure methane flow. Experimental tests were conducted in the temperature range 860–995 °C at atmospheric pressure in an electrically heated reactor. The results showed complete chemical conversion of methane to synthesis gas in the aforementioned temperature range. In addition, analysis of the product solids indicated that the collected solids in the outlet of the reactor were entirely zinc. The maximum methane flow rates (149–744 mL min^–1) were adjusted to ensure complete chemical conversion of methane. These adjustments were performed for different bed heights at various operating temperatures. Analysis of the product gases revealed high quality synthesis gas production without the influence of methane cracking or other undesired side reactions in the experimental tests. Finally, the governing partial differential equations of the reactor modeling were solved by the finite element method. Consequently, the gaseous profiles along the reactor and the breakthrough curves were predicted and compared with the experimental tests.     

Extremes of conversion in continuous-flow reactors

The strong bounding theorem of micromixing has been proved using Bellman's principle of optimality. If the reaction rate depends on the concentration of a single component and is either a concave-upward or concave-downward function of that concentration, the conversion will attain extreme values when the reactor is completely segregated or is in a state of maximum mixedness. The extreme is a maximum when the reaction is concave-down (e.g. order less than one) and the reactor is maximally mixed and a minimum when the reactor is completely segregated. Conversely, the extreme is a minimum when the reaction is concave-up (e.g. order greater than one) and the reactor is maximally mixed and a maximum when the reactor is completely segregated.The new proof eliminates the need for the restrictive assumption that molecules can mix only when they have the same residual life. This assumption is untrue for many reactor models that approximate real physical behaviour.     

Carbon nanotubes for catalytic applications

The unique properties of carbon nanotubes, a new class of nanomaterials, make them usable as catalyst supports for various reactions. A pilot reactor has been constructed for producing nanotubes. The nanotubes obtained in this reactor have displayed high performance in a number of catalytic processes. A continuous laboratory-scale reactor for the synthesis of binary and mixed oxide nanosized catalysts has been tested. Russia has everything necessary for organizing nanotube production.     

Thermolysis of methane in a solar reactor for mass-production of hydrogen and carbon nano-materials

Solar thermolysis of methane to produce hydrogen and carbon nano-materials in a volumetric reactor/receiver with carbon particles cloud either priory seeded or chemically produced in the reactor, has been developed and tested. The reactor is based on absorbing of the concentrated solar radiation by the carbon particles and maintaining a reaction core at high temperature while the reactor walls are kept at relatively low temperatures, compatible with existing ceramic materials. The main advantage of the volumetric approach lies in its excellent heat transfer effectiveness and scalability to larger scales. As a result of computational fluid dynamics (CFD) analysis a compound reactor was designed and tested. The reactor’s most important characteristics are: high reaction temperature, transparent window protection and directional streaming flow (tornado) without boundary layer separation. Experimentally, high temperatures (up to 1500 °C) in the reaction domain were achieved resulting in complete conversion of methane to hydrogen and solid carbon nano particles. Experiments were operated for periods of about 60 min with steady-state temperatures and reaction products. Organometallic catalysts were mixed together with the methane feed to produce multiwalled carbon nanotubes (MWCNT). In the catalytic experiments lower temperatures were maintained which, although resulted in lower methane conversion, enhanced the MWCNT production.