撞击流反应器用于甲醇合成反应

撞击流反应器用于气液固三相甲醇合成反应可以充分发挥其优良的传热、传质性能。在撞击流反应器内,催化剂浆料经喷嘴雾化后成微米尺度的液滴,气液相间接触面积远大于其他三相合成反应器。考察了温度、压力、气体流量、浆料循环量以及喷嘴个数对甲醇合成反应的影响,结果表明,当压力从3.8 MPa上升到5 MPa时,反应器的时空产率增长了近1倍,气体流量达22.4 L·min^-1后时空产率几乎不再变化,增加浆料循环量以及在同一循环量下采用多喷嘴对置都可以增加催化剂时空产率。同时,与固定床、搅拌釜和浆态鼓泡床甲醇合成进行了对比,结果表明,在低空速下撞击流反应器与其他反应器时空产率相当,而在高空速下要优于其他反应器。     

低温液相甲醇合成鼓泡浆态反应器数学模拟

建立了经由甲酸甲酯的低温液相甲醇合成鼓泡浆态反应器的数学模型 ,模拟了实验室鼓泡浆态反应器的行为 ,并利用模型考察了工艺参数如表观气速、催化剂浓度对反应的影响 ,对改进和提高低温液相浆态床反应器甲醇合成提供了信息 ,以便对开发低温甲醇合成工艺提供参考和指导     

Assessment of micro-structured fixed-bed reactors for highly exothermic gas-phase reactions

The application of micro-structured fixed-bed reactors for highly exothermic partial oxidation reactions and their comparison to established multi-tubular fixed-bed reactors was investigated by numerical simulation. As examples, the partial oxidations of butane to maleic anhydride and of o-xylene to phthalic anhydride were chosen. The simulation results revealed that the reactor productivity, i.e. the amount of product per unit of reactor volume, achievable in micro-structured fixed-bed reactors is between 2.5 and 7 times higher than in conventional multi-tubular fixed-bed reactors without the danger of excessive pressure drop. For the partial oxidation of butane to maleic anhydride this can be explained by the increased reactor efficiency caused by lower efficiency losses through heat and mass transfer limitations. In addition, maleic anhydride selectivities and yields are higher in micro-structured fixed-bed reactors. In the case of o-xylene oxidation to phthalic anhydride the main advantage is that egg-shell catalysts in the conventional fixed-bed reactor can be replaced by bulk catalysts in the micro-structured fixed-bed reactor. For this reaction, product selectivities are very similar for all reactor configurations. Thus the catalyst inventory and reactor productivity are strongly increased. This study underlines, that micro-structured fixed-bed reactors exhibit the potential to intensify large scale industrial processes significantly.     

On the relevance of mass transfer limitations in the Fischer-Tropsch slurry process

Satterfield and Huff[1] reported recently on significant mass transfer resistances in the FT slurry process. However, their conclusions are at least partly based on a study with an unsuitable catalyst. In the present communication FT studies with 8 different catalysts and bubble columns, respectively, were analyzed using new and reliable results on hydrodynamic properties. In all cases, mass transfer resistances were found to be small compared to reaction resistances. As long as much more active catalysts are not developed significant mass transfer limitations cannot be expected in the bubble column if operated under appropriate conditions. The absence of mass transfer limitations is mainly a result of the high gas holdups attainable with molten paraffin as liquid phase.     

DIRECT OXIDATION OF ETHYLENE TO ACETALDEHYDE IN A HOLLOW FIBER MEMBRANE REACTOR†

A hollow fiber membrane reactor, which resembles a tube-and-shell heat exchanger, was developed for homogeneous catalytic reactions with gas reactants and products. The gas stream flows through the tube side while the reaction takes place in the catalyst solution which fills the shell side. The separation load of product from the catalyst solution can be reduced by using a hollow fiber membrane reactor instead of a conventional bubble column reactor. The reactor operates in a plug-flow pattern with a large mass transfer area per unit volume of catalyst solution

This concept was investigated experimentally using the direct oxidation of ethylene to acetaldehyde reaction in an aqueous solution of palladium (H) chloride-cupric chloride with a silicone rubber membrane reactor and a polypropylene membrane reactor. It was experimentally demonstrated that membrane reactors could achieve higher production rates per unit volume of catalyst than the conventional sparged reactor. The experimental data were in good agreement with the predictions by the mathematical model. The conditions under which the membrane reactor will be more advantageous than the conventional sparged reactors can be readily ascertained with the analytical solution of the simplified membrane reactor model.     

Simulation of structured catalytic reactors with enhanced thermal conductivity for selective oxidation reactions

The replacement of conventional-packed beds of pellets with “high conductivity” honeycomb catalysts in industrial externally cooled multitubular fixed-bed reactors is investigated by modeling and simulation for the oxidation of methanol to formaldehyde and for the epoxidation of ethylene to ethylene oxide, which involve a consecutive and a parallel reaction scheme, respectively. Results suggest that near-isothermal operation of the fixed-bed reactors can be achieved using monolithic catalyst supports based on relatively large volume fractions of highly conductive materials. Pressure drops are reduced to less than 1%. The selectivity is favored by the excellent control of the intraporous diffusional resistances resulting from the thin catalytic washcoats. Reactor designs based on larger tubes are feasible at the expense of greater volume fractions of catalyst support. A critical aspect is represented by the restrictions on the specific load of catalyst per reactor volume resulting from the poor adhesion of very thick catalyst layers onto metallic surfaces. Such a difficulty can be circumvented by maximizing the geometric surface area of the monolith (e.g. minimizing the honeycomb pitch), enhancing the catalytic activity (e.g. increasing the load of active components), and increasing the coolant temperature (if the selectivity is not adversely affected).     

A novel slurry bubble column membrane reactor concept for Fischer–Tropsch synthesis in GTL technology

Fischer–Tropsch synthesis (FTS) plays an important role in the production of ultra-clean transportation fuels, chemicals, and other hydrocarbon products. In this work, a novel combination of fixed-bed and slurry bubble column membrane reactor for Fischer–Tropsch synthesis has been proposed. In the first catalyst bed, the synthesis gas is partially converted to hydrocarbons in a water-cooled reactor which is fixed bed. In the second bed which is a membrane assisted slurry bubble column reactor, the heat of reaction is used to preheat the feed synthesis gas to the first reactor. Due to the decrease of H₂/CO to values far from optimum reactants ratio, the membrane concept is suggested to control hydrogen addition. A one-dimensional packed-bed model has been used for modeling of fixed-bed reactor. Also a one-dimensional model with plug flow pattern for gas phase and an axial dispersion pattern for liquid-solid suspension have been developed for modeling of slurry bubble column reactor. Proficiency of a membrane FTS reactor (MR) and a conventional FTS reactor (CR) at identical process conditions has been used as a basis for comparison in terms of temperature, gasoline yield, H₂ and CO conversion as well as selectivity. Results show a favorable temperature profile along the proposed concept, an enhancement in the gasoline yield and, thus a main decrease in undesirable product formation. The results suggest that utilizing this type of reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the proposed reactor.     

三相鼓泡淤浆床环氧乙烷合成反应器数学模拟及工程分析

建立了加压三相鼓泡淤浆床环氧乙烷合成反应器的数学模型 ,计入了催化剂颗粒在床层中沉降形成沿床高浓度分布对反应的影响以及由于惰性液相载体部分返混对传递的影响 ,进一步利用经实验验证的上述数学模型模拟不同表观气速、床高、反应器直径 (扣除传热元件截面积 )、进口乙烯摩尔分数等参数对床层中催化剂浓度随床高的分布、出口环氧乙烷摩尔分数、环氧乙烷选择率以及单位质量催化剂环氧乙烷年产量的影响 .通过模拟分析预示了工业三相床环氧乙烷反应器的合理尺寸、表观气速、环氧乙烷选择率以及时空产率 ,为工业化提供必要的设计依据     

Fast gas–liquid–solid reactions in monoliths: A case study of nitro-aromatic hydrogenation

Monolith catalyst supports are attractive as fixed bed reactors that, at the scale of the catalyst dimension, exhibit the mass transfer characteristics of slurry reactors. This paper presents a reactor design study for the single-pass conversion of dinitrotoluene in a loop configuration with an external heat exchanger. The advantage of such a loop system is the elimination of a solvent, which in turn allows more reaction heat to be recovered. The advantages of using a monolith are the low pressure drop at high recycle ratio, while maintaining good mass transfer characteristics. The modelling includes internal diffusion limitation, external mass transfer characteristics, heat effects, maldistribution and flow stability. The optimal design is found at the lowest hydrodynamic stable flow rates, where the mass transfer is fastest and the residence time in the column maximal.     

Hydrodynamics and mass transfer in an upward venturi/bubble column combination

The hydrodynamics and mass transfer characteristics of a venturi/bubble column combination were studied at high liquid superficial velocities of up to 0.35 m/s. The gas hold-up was increased by 50% to 150% and the overall volumetric mass transfer coefficient was tripled when the venturi was used as “gas distributor” instead of a porous distributor. A correlation of the overall volumetric mass transfer coefficient (K_La) with the gas hold-up, valid for gas hold-ups as high as 0.3, was proposed for the cylindrical bubble column section. The energy consumption per mole of oxygen transferred was lower than with most distributors and the oxygen transfer rate per unit of reactor volume was higher than in a bubble column with a porous distributor. The venturi/bubble column combination is a compact and efficient system which does not have the operating problems of systems which require internals.     

Similar effect of carbon and silica catalyst support on the hydrogenation reaction rate in organic slurry reactors

This paper investigates the influence of the catalyst support type on mass transport and reaction rate for the case of hydrogenation of α-methylstyrene to cumene in a gas inducing stirred slurry reactor and in a slurry bubble column. The reaction is carried out in the presence of 3% Pd/carbon and 3% Pd/silica catalyst particles. The lyophobicity of the two catalyst supports in the cumene slurry is found to be similar. The overall rate of the hydrogenation reaction is described by the classical transport and reaction resistances-in-series model. The rate of gas-to-liquid mass transfer is somewhat larger during reaction than without reaction. This enhanced mass transfer points to particle-to-bubble adhesion as a result of the relative affinity of both catalyst supports to the gas phase. The observed reaction enhancements are similar for both Pd/carbon and Pd/silica catalyst/cumene slurries.     

A new photocatalytic reactor for destruction of toxic water pollutants by advanced oxidation process

A new photocatalytic reactor design for water treatment is presented, characterized by the use of new extremely narrow diameter lamps, thus allowing for much higher surface area for catalyst coating per unit reactor volume and consequently for much higher specific reactor capacity. Experiments in a reactor containing 21 novel U-shaped lamps coated with the catalyst showed 695% increase in efficiency of the reactor performance when compared with classical annular reactor, 260% when compared with a slurry reactor, and 60% when compared with a multiple tube reactor. The classical annular reactor and slurry reactor cannot be scaled-up for large-scale applications due to the low values of an illuminated catalyst surface area per unit volume of liquid treated inside the reactor. In the multiple tube reactor the above problem could be eliminated, but it suffers from the disadvantage that uniform light intensity cannot be achieved. Development of a reactor using the new lamps will provide all the advantages of the multiple tube reactor, plus the additional advantage that the catalyst could be activated at its highest level. The present configuration is flexible enough for large-scale applications.     

浆态鼓泡床反应器气液传质特性的研究进展

本文总结了有关浆态鼓泡床反应器气液传质特性的研究成果。详细地阐述了主要影响因素如系统压力、温度、气体表观气速、液体性质,固体浓度及其物性等对传质特性的影响,并对浆态鼓泡床传质模型进行了归纳介绍,最后对反应器未来的研究方向进行了预测。     

Bubble Column Reactors and Fischer-Tropsch Synthesis

Three-phase slurry bubble column reactors have been used extensively in a number of chemical, petrochemical, and biochemical process engineering applications. For the success of these operations and their large scale industrial exploitation, it is essential that their transport and chemical characteristics be adequately understood on a mechanistic basis so that appropriate design criteria and optimum operating conditions can be established. It is the purpose of this review to present such available knowledge in relation to chemical catalytic operations. The mass transfer characteristics, catalytic activity, and mixing patterns of different phases necessitate a detailed understanding of the hydrodynamic behavior and catalyst dispersion in slurry bubble column reactors. The current status of these aspects is presented, discussed, and assessed in this review. Chemical and biochemical reactions are exothermic in nature and hence efficient heat removal devices must be installed in the reactor to preserve its isothermal behavior and chemical catalytic activity by avoiding temperature runaway. Extensive work recently conducted from this heat transfer viewpoint is reviewed and appraised. The bubble dynamics, and slurry mixing and movement characteristics of such baffled bubble columns are significantly different from those of unbaffled bubble columns. Very limited information is available on baffled bubble column operations and this is reviewed and critically examined. An important application of the slurry bubble column is in the synthesis of fuel gases on suspended catalyst particle surface to produce chemicals. One such example is the Fischer-Tropsch synthesis of hydrogen and carbon monoxide in what is referred to as indirect coal liquefaction technology. Pilot plant efforts of this nature and their successes are briefly mentioned. Mathematical details and models developed from time to time to characterize catalytic bubble column operations are briefly described and discussed. In the context of available information and its integration presented here, the specific needs for future experimental and theoretical research work are pointed out.     

Study on a catalytic distillation column with a novel internal

A novel internal for holding a catalyst in a catalytic distillation column was studied and its feasibility was verified by a model reaction, which is the alkylation of benzene with propylene over Hβ zeolite catalyst. The novel internal enlarges the void of the catalyst bed and provides the gas and liquid flow channels. It was proved that the catalytic distillation column with the novel internal has such advantages as simple structure, low operating cost, convenience for loading and unloading catalyst, and large catalyst loading fraction. It was found that the operational capability of the column with the novel internal whose volume fraction is about 30% is similar to that of a column filled with catalysts mixed with Cannon rings whose volume fraction is about 80%. It was also found that compared with the fixed-bed bubble reactor, the selectivity of cumene and the conversion of benzene are significantly improved in the CD (Catalytic Distillation) column with the internal.     

高固含率三相鼓泡淤浆反应器气液传质研究及其采用两种气体分布器的比较

以空气-水-黄沙以及空气-液体石蜡-黄沙两种系统为对象，在常压下用溶氧仪研究了采用小孔式及金属烧结板两种分布器的高固含率三相淤浆反应器的气液传质特性，以及固含率和表观气速等因素对容积气液传质系数kLa的影响，最后得到采用上述两种气体分布器的高固含率三相淤浆床关于容积气-液传质系数的经验关联式。实验证明，金属烧结板具有更好的气液传质特性。     

STUDY ON A CATALYTIC DISTILLATION COLUMN WITH A NOVEL INTERNAL

A novel internal for holding a catalyst in a catalytic distillation column was studied and its feasibility was verified by a model reaction, which is the alkylation of benzene with propylene over Hβ zeolite catalyst. The novel internal enlarges the void of the catalyst bed and provides the gas and liquid flow channels. It was proved that the catalytic distillation column with the novel internal has such advantages as simple structure, low operating cost, convenience for loading and unloading catalyst, and large catalyst loading fraction. It was found that the operational capability of the column with the novel internal whose volume fraction is about 30% is similar to that of a column filled with catalysts mixed with Cannon rings whose volume fraction is about 80%. It was also found that compared with the fixed-bed bubble reactor, the selectivity of cumene and the conversion of benzene are significantly improved in the CD (Catalytic Distillation) column with the internal.     

LIQUID-PHASE MASS TRANSFER COEFFICIENT IN SLURRY BUBBLE COLUMN REACTORS: THEORY AND EXPERIMENTAL DATA IN SIMULATED FERMENTATION MEDIA

Mass transfer in a slurry bubble column reactor was examined. A theoretical correlation for liquid-phase mass transfer coefficient was developed using a combination of Higbie's penetration theory and the Einstein-Li periodic viscous sublayer model. The proposed correlation predicts that the liquid-phase mass transfer coefficient decreases with an increase of the yield stress of slurries. The measurement of mass transfer rates was conducted in a 40-L bubble column reactor. The slurries containing low-density particles were simulated by aqueous carboxypolmethylene solutions. Satisfactory agreement was found between the proposed correlation and the experimental data.     

Low-temperature methanol synthesis in a circulating slurry bubble reactor

A circulating slurry bubble reactor was developed to synthesise methanol via methyl formate from the gas mixture of carbon monoxide and hydrogen at low temperature. The strategy for designing and scaling up the bubble reactor involved a preliminary understanding of fluid dynamics in a cold model, continuous operations under industrial conditions and a parallel experiment in an autoclave. Per-pass syngas conversion was investigated during 100-h operations. The axial profile of solid catalyst concentration was measured just before the shutdown and the composition of liquid product was analysed after the shutdown. These results show that the circulating slurry bubble column will become a potential reactor for the commercial process of low-temperature methanol synthesis after the catalyst system has been improved.     

高温高压浆态鼓泡床反应器中的气-液传质

The gas-liquid mass transfer of H2 and CO in a high temperature and high-pressure three-phase slurry bubble column reactor is studied. The gas-liquid volumetric mass transfer coefficients kLa are obtained by measuring the dissolution rate of H2 and CO. The influences of the main operation conditions, such as temperature, pressure,superficial gas velocity and solid concentration, are studied systematically. Two empirical correlations are proposed to predict kLa values for H2 and CO in liquid paraffln/solid particles slurry bubble column reactors.