Comparison of Vinyl Acetate - Butyl Acrylate Emulsion Copolymerizations Conducted in a Continuous Pulsed Sieve Plate Column Reactor and in a Batch Stirred Tank Reactor

In this work, vinyl acetate/butyl acrylate emulsion copolymerizations carried out in a continuous tubular reactor (pulsed sieve plate column, PSPC) were compared to those conducted in a semibatch stirred tank reactor under similar operational conditions. In order to minimize the compositional drift along the PSPC, reactions were carried out with different numbers (2, 3 and 4) of lateral feed streams of the more reactive monomer (butyl acrylate). For comparison, fed batch reactions were conducted with the same number of intermittent shot additions of butyl acrylate, at the corresponding batch times. Both systems (tubular and semibatch) with distributed feeding of more reactive monomer are able to reduce composition drift thus providing more uniformity in copolymer composition. In addition, the tubular reactor presents much better control of temperature than the tank reactor, which is important to achieve higher productivity.     

铈改性丝光沸石在甲醇胺化反应中的应用

研究了氨和甲醇以铈改性丝光沸石为催化剂,在常压固定床上选择性合成二甲胺的反应。考察了温度、氨醇比、甲醇液相空速等制备条件对催化剂的活性及二甲胺选择性的影响。     

Experimental investigations of liquid flow in pipe with flat internal baffles

Liquid flow in a tubular reactor with flat internal baffles of various widths was investigated. On the basis of the laser Doppler anemometry (LDA) measurements, the main flow parameters, i.e. the mean and fluctuating velocity components and turbulent kinetic energy (TKE) were determined. The investigations demonstrated that the insertion of baffles into a pipe and a change in their width caused a generation of liquid stream whirls, induced liquid recirculation loops and intensified the flow considerably. The results can be useful in describing turbulent flow in tubular reactors with baffles and in optimising their design.     

Production of porous suspension polymers using a continuous tubular reactor

The conventional method for the synthesis of porous cross-linked copolymer beads is by suspension polymerisation. Suspension polymerisation reactions are generally performed in a stirred tank, which generally results in a large size distribution. By careful control of the polymerisation conditions, polymer beads can be produced using a tubular poly(tetrafluoroethylene) continuous reactor. Such beads are produced with the same average pore size, but with a lower degree of polydispersity than analogous systems produced in a batch reactor (stirred tank). This is achieved by density-matching the droplet and continuous phases (by the use of a brominated monomer or a porogenic diluent) and increasing the viscosity of the monomer phase (with the addition of small amounts of polystyrene). Received: 26 June 1999/Accepted in revised form: 7 October 1999     

一种改进的脱水方式对费托合成铁基催化剂结构性质与催化性能的影响

研究了一种改进的脱水方式对费托(F-T)合成铁基催化剂结构性质与催化性能的影响.在n(H2)/n(CO)=0.67,WHSV=1000 h-1,p=1.5 MPa和t=250 ℃的条件下对催化剂进行了浆态床F-T合成反应性能评价实验,并采用低温N2物理吸附、X射线衍射、原子发射光谱、X射线光电子能谱、氨程序升温脱附、穆斯堡尔谱和高分辨透射电镜等技术对催化剂进行了表征.结果表明,水处理和二次干燥得到的催化剂比表面积增加,颗粒减小,铁氧化物的分散程度增大,其表面的SiO2/Fe比例明显减小;该催化剂F-T合成反应活性有所增加;表面酸性有所增强,导致烃产物选择性向低碳数方向偏移.     

The reaction kinetics of dimethyl ether. I: High‐temperature pyrolysis and oxidation in flow reactors

Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions. Pyrolysis of dimethyl ether was studied in a variable‐pressure flow reactor at 2.5 atm and 1118 K. Studies were also conducted in an atmospheric pressure flow reactor at about 1085 K. These experiments included trace‐oxygen‐assisted pyrolysis, as well as full oxidation experiments, with the equivalence ratio (ϕ) varying from 0.32 ≤ ϕ ≤ 3.4. On‐line, continuous, extractive sampling in conjunction with Fourier Transform Infra‐Red, Non‐Dispersive Infra‐Red (for CO and CO₂) and electrochemical (for O₂) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactors. Species concentrations were correlated against residence time in the reactor and species evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism. Some changes were made to the model in order to improve agreement with the present experimental data. However, the revised model continues to reproduce previously reported high‐temperature jet‐stirred reactor and shock tube results. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet: 32: 713–740, 2000     

RESEARCH AND DEVELOPMENT OF FUEL ALCOHOL SYNTHESIS FROM SYNGAS

The research and development of catalyst preparation and catalytic technology for fuel alcohol synthesis from syngas have been conducted. The laboratory research work includes the investigation on the effects of preparation method, the composition and K2O content on the catalyst performance. The influences of reaction temperature, pressure, GHSV and feed composition on higher alcohols synthesis have also been investigated. On the basis of laboratory results, the catalysts have been further tesied in micro-pilot reactor under the industrial condition to investigate the effects of commercial preparation of catalyst, the reactor scaling up and (he use of industrial coal based syngas on the fuel alcohol ( mixture of methanol and higher alcohols ) synthesis. The catalyst stability has been tested by a 1000 h continuous operation. These provide the fundamental for further commercial plant design.     

Intrinsic Kinetics of Dimethyl Ether Synthesis from Syngas

The intrinsic kinetics of dimethyl ether (DME) synthesis from syngas over a methanol synthesis catalyst mixed with methanol dehydration catalyst has been investigated in a tubular integral reactor at 3-7MPa and 220-260℃. The three reactions including methanol synthesis from CO and H2, CO2 and H2, and methanol dehydration were chosen as the independent reactions. The L-H kinetic model was presented for dimethyl ether synthesis and the parameters of the model were obtained by using simplex method combined with genetic algorithm. The model is reliable according to statistical analysis and residual error analysis. The synergy effect of the reactions over the bifunctional catalyst was compared with the effect for methanol synthesis catalyst under the same conditions based on the model. The effects of syngas containing N2 on the reactions were also simulated.     

Simulation of Polymer Reactors Using the Compartment Modeling Approach

A compartment modeling approach based on computational fluid dynamics (CFD) simulations is applied to a simplified static mixer geometry. Compartments are derived from velocity fields obtained from cold CFD simulations. This methodology is based on the definition of periodic flow zones (PFZ) derived from the recurrent flow profile within the static mixer. In general, PFZ can be characterized by two different compartments: flow zones with hydrodynamic behavior of a tubular reactor and dead zones exhibiting a more continuous stirred tank reactor‐like characteristic. In CFD studies the influence of changing fluid properties, for example viscosity, on flow profile due to polymerization progress is considered. In the deterministic compartment model, the continuous flow profile within the static mixer is transformed to basic reactor models interconnected via an exchange stream. To reduce model complexity and the number of model parameters, constant volumes of compartments are assumed. Changes in hydrodynamics are considered by a variable exchange flow rate as a function of Re manipulating residence time in compartments. Simulation studies show the influence of decreasing exchange flow rates with polymerization progress, as Re decreases, resulting in a greater increase of viscosity in dead zones. The reactor performance is qualitatively represented by the simulation results.     

Economic evaluation of the hydrolysis of lactose using immobilized β-galactosidase

A computer program for preliminary cost estimates of free and immobilized enzyme systems has been developed. The cost for the hydrolysis of lactose by β-galactosidase fromAspergillus oryzae has been calculated for a batch tank reactor, with free (BTRF) and immobilized (BTRI) enzymes, a continuously stirred tank reactor (CSTR) and a plug-flow tubular reactor (PFTR), considering the mass transfer behavior and deactivation of the enzyme.

Enzyme immobilization is economically feasible, compared with a system with free enzymes, despite a very high cost for the enzyme attachment. At a half-life time of 80 d, the PFTR gives the lowest cost (0.48 SEK/kg lactose), but the cost for the BTRI is just slightly higher (0.66 SEK/kg lactose) and still much lower than the BTRF (2.10 SEK/kg lactose).

     

Magnetic resonance imaging of flow-distributed oscillations

The formation of stationary concentration patterns in a packed-bed reactor (PBR), using a manganese-catalyzed Belousov-Zhabotinsky (BZ) reaction in a mixed sulfuric-phosphoric acid medium, was studied using magnetic resonance imaging (MRI). The PBR was composed of a column filled with glass beads, which was fed by a continuous stirred tank reactor (CSTR). As the reactor is optically opaque, investigation of the three-dimensional (3D) structure of these reaction-diffusion-advection waves is not possible using conventional image capture techniques. MRI has been used to probe this system and the formation, 3D structure, and development of these waves has been studied. At reactor startup, traveling waves were observed. After this initial period the waves stabilized and became stationary. Once fixed, they were found to be remarkably stable. There was significant heterogeneity of the reaction fronts, which were not flat, as would be expected from a plug-flow reactor. Instead, the reaction wave fronts were observed to be conical in shape due to the local hydrodynamics of the bed and specifically the higher velocities and therefore lower residence times close to the wall of the reactor.     

沸石与酸性水溶液反应的动力学机制

利用连续搅拌筒反应器(CSTR)对天然沸石与酸性水溶液的反应动力学进行研究, 通过改变流速、 pH值等参数, 对反应速率进行计算和比较. 同时利用二次离子质谱(SIMS)、扫描电镜(SEM)对反应后的沸石表面进行分析研究. 实验结果表明, 沸石中的Si、Al、Na的释放速率在多数情况下不相同, 沸石的溶解为不一致溶解作用. 25 ℃、1.01×10⁵ Pa条件下, 硅的释放速率为：在pH=2.45溶液中反应时, -rSi=kS(aH+)1.25/ (aSi)0.60；在pH=3.26溶液中反应时, -rSi=kS(aH+)1.50/(aSi)0.25(S为矿物材料的表面积). SIMS研究显示, 天然沸石与酸性水溶液的反应中, 在沸石表面Si、Al、Na在100 nm的厚度范围内, 随着离表面距离的改变, 在近表面范围内Na、Al大量淋失, 有H⁺浸入. 此外, SEM分析结果显示, 天然沸石与纯水及酸性水溶液反应后, 表面形貌显著不同.     

Kinetic Study of the Copolymerisation of Ethylene with a Single Site Catalyst in Propane Slurry Polymerisation

Summary: The kinetic behaviour of a supported metallocene catalyst in slurry polymerisation of ethylene with 1-hexene under industrially relevant reaction conditions has been studied. Polymerisation experiments were carried out in a 5-litre stirred tank reactor in a temperature range from 60 to 80 °C and ethylene partial pressures from 5 to 15 bar. Comonomer and hydrogen amounts were varied as well. The catalyst showed pronounced activation and slow deactivation during runtimes of about 1 hour. Strong influences of 1-hexene (“hexene effect”) and hydrogen (“hydrogen effect”) on the activity profiles were observed. Based on the experimental results, a kinetic model has been derived in order to describe and predict important polymerisation data such as activity profile, comonomer content and molecular weight distributions with respect to the reaction conditions. The presented kinetic model is able to describe the observed effects of 1-hexene and hydrogen on the activity profiles, as well as the comonomer incorporation across a broad range of polymerisation conditions. The molecular weight distributions can be simulated with good qualitative agreement to the experimental data.     

Evaluation of mass-transfer and kinetic parameters forRhodospirillum rubrum in a continuous stirred tank reactor

The photosynthetic bacteriumRhodospirillum rubrum has been evaluated for its ability to produce hydrogen from carbon monoxide and water in a continuous stirred tank reactor according to the watergas shift reaction. An assessment of mass-transfer parameters and reaction kinetics was made for this sparingly soluble substrate system. Experiments were conducted in a nonsteady-state fashion with continuous liquid and gas flow, which allowed for separation of the mass-transfer and kinetic-limited regions. Based on the data obtained, mass-transfer coefficients for the system were determined, and a mathematical expression for the reaction kinetics was formulated. The results showed that the hydrogen production was inhibited by elevated levels of dissolved carbon monoxide in the liquid.     

In situ Fourier transform infrared spectroscopy as an efficient tool for determination of reaction kinetics

The performance of new FTIR-based monitoring technology to representatively determine reaction kinetics has been demonstrated on an example of homogeneously catalyzed liquid-phase sucrose hydrolysis to fructose and glucose. The reaction kinetics were investigated by using the ReactIR 1000 reaction analysis system, which enables determination of the component concentration from its characteristic FTIR spectrum. During the sucrose inversion, the ReactIR 1000 instrument connected to a computer controlled standard glass batch reactor provided the required operating conditions and information about the component concentration in real-time. We have studied the influence of hydrogen ion concentration, temperature and initial concentration of sucrose on the sucrose disappearance rate. It was found out that the inversion of sucrose is an irreversible reaction, which is not affected by the formation of fructose and glucose in the liquid-phase. Then, the parameters of the kinetic model (i.e., reaction rate constant and activation energy) were calculated. A comparison of the model output and the measured data showed that the kinetics of the sucrose inversion could be well described by means of the pseudo first-order kinetic model. Finally, the method of determining the kinetic model by FTIR spectroscopy was verified by comparing the results obtained in the batch reactor with the results obtained in the continuously stirred tank reactor.     

高碘酸盐-硫脲-硫酸反应体系的非线性动力学

研究了KIO4 SC(NH2)2 H2SO4反应体系在封闭、半封闭以及开放系统中的非线性动力学行为.发现在封闭体系中体系的吸光度、铂电极电位和pH值呈现单峰或准振荡现象；在半封闭和开放系统中体系的铂电极电位和碘电极电位均呈振荡现象.封闭、半封闭及开放系统的动力学曲线受体系酸度和初始浓度比值[KIO4]0/[SC(NH2)2]0的影响.对照其在封闭、半封闭和开放系统中的动力学行为,以碘单质产生和消耗驱使的反应动力学可解释该反应体系的复杂现象.     

高碘酸盐-硫脲-硫酸反应体系的非线性动力学

研究了KIO4-SC(NH2)2-H2SO4反应体系在封闭、半封闭以及开放系统中的非线性动力学行为.发现在封闭体系中体系的吸光度、铂电极电位和pH值呈现单峰或准振荡现象;在半封闭和开放系统中体系的铂电极电位和碘电极电位均呈振荡现象.封闭、半封闭及开放系统的动力学曲线受体系酸度和初始浓度比值犤KIO4犦0/犤SC(NH2)2犦0的影响.对照其在封闭、半封闭和开放系统中的动力学行为,以碘单质产生和消耗驱使的反应动力学可解释该反应体系的复杂现象.     

Application of an intensified narrow channel reactor to the aqueous phase precipitation of barium sulphate

A homogeneous liquid phase reaction between barium chloride (BaCl(2)) and sodium sulphate (Na(2)SO(4)) was conducted in a narrow channel reactor to produce barium sulphate (BaSO(4)) precipitate. The effects of channel dimensions and channel residence times on crystal size, crystal size distribution, nucleation rates, crystal morphology and conversion of reactants were investigated at different levels of reactant supersaturation ratio. Our results indicate that the smallest particle sizes are favoured when supersaturation ratios and channel velocities are high. The minimum average particle diameter observed was approximately 0.2 microm in a channel of hydraulic diameter 0.5 mm and length 20 cm at an initial supersaturation ratio of 4483 (0.1 M), which correspond to conditions giving rise to the highest nucleation rates. It has also been observed that particle size depends on the conversion to product, the smallest particles being formed when conversion lies within the range of 30 to 40%. Conversions in excess of 60% have been reached but there is a detectable limiting effect with increased supersaturation and reduced residence times. Experiments conducted at similar levels of supersaturation under stirred tank conditions showed that particle size was consistently larger and particle size distribution was much broader than that achieved in the narrow channel reactor. Scanning electron microscopy (SEM) images of the crystals formed in the narrow channels show that spherical particles dominate in the smallest channels at high velocities whilst coarse, tabular crystals are obtained in the larger channels. Greater tendency to agglomerate is also observed at high supersaturation ratios, after one minute of reaction.     

Cu、K助剂对FeMn/SiO2催化费托合成的影响

研究了Cu、K助剂对共沉淀型FeMn/SiO2催化剂还原行为、吸附行为及费托(F-T)合成活性和选择性的影响. Cu助剂以与Fe、Mn、SiO2共沉淀的方式引入, 而K助剂是在喷雾干燥前均匀加入沉淀浆料引入的. 结果表明, Cu可明显提高催化剂的还原性能, K助剂能促进催化剂在CO中的还原但抑制在H2中的还原, 而同时加入Cu和K会进一步促进催化剂在H2或CO中的还原; Cu助剂能促进H2吸附而K助剂对H2吸附无明显影响; Cu在一定程度上提高了F-T合成活性, 缩短了反应诱导期, K明显促进了CO的转化而相对抑制了H2的转化, 并且延长了反应的诱导期, Cu与K协同作用不仅提高反应的转化率而且缩短了反应的诱导期; K使得烃产物平均分子量增加, Cu单独对烃产物分布影响不明显, 而与K共同作用会进一步增加烃产物的分子量.