Selective detection in flow analysis based on the combination of immobilized enzymes and chemically modified electrodes

The combination of immobilized enzymes and amperometry to build selective detection devices in flow-injection analysis and liquid chromatography is described. The pros and cons of enzyme electrodes and of immobilized enzyme reactors are discussed. The paper concentrates on the use of immobilized dehydrogenases, oxidases, peroxidases, and on electrodes on which these enzyme reactions can be selectively followed. The work in the field by the authors is reviewed.     

Mixing study of the induction plasma reactor: Part II. Radial injection mode

A study was undertaken on the mixing pattern in am induction plasma torch and reactor system. The results presented in this part of the paper relate to the radial injection mode, in which an auxiliary gas is injected into the main plasma stream through a set of 2, 4, or 8 injection ports located in the torch nozzle at the level of the torch exit flange. A much faster mixing of the gases occurred in this mode compared to the axial injection mode investigated in Part I of this paper. As in the case of axial injection, the present study demonstrates that gas mixing, in the presence of the discharge, is considerably more difficult than under ambient temperature conditions. Lower turbulence levels exist in the plasma reactor. due to the considerably higher viscosity of the gases under plasma conditions. Results obtained with a three-point injection flange, in which the injection ports were oriented at 45° to the torch and reactor axes toward the upstream .side, mere most interesting since they achieved essentially the same degree of mixing as was obtained with the radial injection ports without the need to locate the injection ports at the exit nozzle of the plasma torch. This arrangement provides for added flexibility in reactor design.     

用于筛膜反应器的γ-MnO2纳米粉的合成

醋酸锰与柠檬酸发生沉淀反应生成锰配合物,经热分解和酸处理手段最终制备出γ MnO2纳米材料,用X射线衍射、差热/热重分析、透射电镜及原子力显微镜等手段对合成的样品进行了表征.同时考察了反应条件对反应速度、最终产品粒度的影响.结果表明,通过对反应条件的控制可以在一定程度上控制产品的粒度,得到了均粒度和超细粒度的γ MnO2纳米材料.对于异丙醇和环己烷等氧化脱氢反应,γ MnO2纳米筛膜反应器与传统的固定床反应器相比反应物的转化率提高了20％.     

Polymer treatment in the flowing afterglow of an oxygen microwave discharge: Active species profile concentrations and kinetics of the functionalization

The surface treatment of different polymers and their corresponding model surfaces in the flowing afterglow of an oxygen microwave plasma is investigated. The concentration profiles of tire long-lived species issued from the plasma are measured and calculated in the downstream area The influence of atomic and singlet molecular oxygen in the behavior of different polymers is investigated. It appears that the evolution of the surface energy can be explained by an initiation of the functionalization by the oxygen atoms impinging upon the surface followed by reaction of the radicals formed with molecular oxygen. The concentration of functions at the sureface is limited due to their destruction by reaction with oxygen atoms. Furthermore, the functionalization level is higher in the /lowing afterglow than in the plasma, without any significant degradation of the polymer surface. Therefore, the treatment in the flowing afterglow is more efficient to increase suface energy in particular, for polymers which undergo high backbone chain scission.Died April 27, 1993.     

Techniques used to study the chemistry of gas phase elemental clusters

Recent studies of the chemistry of elemental clusters (such as C _n , Si _n , and Fe _n ) in the gas phase have revealed a number of fascinating results. This review article discusses and compares the various techniques that have been used to investigate the chemical properties of gas phase elemental clusters. Examples are provided of the often complimentary information that can be obtained from the different methods.     

Pd encapsulated and nanopore hollow fiber membranes: Synthesis and permeation studies

New types of supported Pd membranes were developed for high temperature H₂ separation. Sequential combinations of boehmite sol slip casting and film coating, and electroless plating (ELP) steps were designed to synthesize “Pd encapsulated” and “Pd nanopore” membranes supported on -Al₂O₃ hollow fibers. The permeation characteristics (flux, permselectivity) of a series of unaged and aged encapsulated and nanopore membranes with different Pd loadings were compared to those of a conventional 1 μm Pd/4 μm γ-Al₂O₃/-Al₂O₃ hollow fiber membrane. The unaged encapsulated membrane exhibited good performance with ideal H₂/N₂ separation factors of 3000–8000 and H₂ flux 0.4 mol/m² s at 370 °C and a transmembrane pressure gradient of 4 × 10⁵ Pa. The unaged Pd nanopore membranes had a lower initial flux and permselectivity, but exhibited superior performance with extended use (200 h). At the same conditions the unaged 2.6 μm Pd nanopore membrane had a H₂ flux of 0.16 mol/m² s and separation factor of 500 and the unaged 0.6 μm Pd nanopore membrane had a H₂ flux of 0.25 mol/m² s and separation factor of 50. Both nanopore membranes stabilized after 40 h of operation, in contrast to a continued deterioration of the permselectivity for the other membranes. An analysis of the permeation data reveals a combination of Knudsen and convective transport through membrane defects. A phenomenological, qualitative model of the synthesis and resulting structure of the encapsulated and nanopore membranes is presented to explain the permeation results.     

Technical and economic evaluation of different reactors for methanotrophic cultures for propylene oxide production

A two-stage process for the manufacture of propylene oxide is described. The preliminary economics based on use of methanol as a regeneration factor has resulted in a production cost of $12.10/lb of propylene oxide based on propylene oxide production rate of 40 mg/g-cell/h in conventional reactor. Increasing the propylene oxide production from 40 to 500 mg/g-cell/h resulted in a cost reduction from $12.10 to 5.8/lb of propylene oxide. The granular-activated, carbon-fluidized bed reactor (GAC-FBR) absorbs the propylene oxide and when saturated is eluted with ethyl acetate, and the bed is regenerated by steam to drive off the residual solvents. The estimated manufacturing costs are approx 59% lower (from $12.10/lb in conventional reactors to $5.00/lb for GAC-FBRs) for products that are highly inhibitory such as epoxides. In the GAC-FBR reactor, enhancing the propylene oxide production rate from 120 to 1500 mg/g-cell/h has resulted in the cost reduction to $2.00/lb. Enhancing the production capacity from 1 million lb to 10 million lb/yr has further reduced the cost of production to $1.00/lb.     

Optimum catalytic reactor design for methanol synthesis with TEC MRF-Z? reactor

The concept of Multi-stage indirect cooling and Radial Flow (MRF) is ideal for designing a catalytic reactor in which an exothermic equilibrium reaction takes place. The reaction is controlled to go on along the path of the maximum reaction rate in the catalyst bed where synthesis gas flows radially in the catalyst beds from the outer side to an inner center pipe across boiler (cooling) tubes to recover the reaction heat as qualitative steam. The MRF concept has already been proven in a commercial scale methanol plant and is unique not only for saving energy but also for considerable scale-up for which the enhanced design, MRF-Z^®, provides. MRF-Z^® is now offered for single train 5,000 t/d reactors used in so-called jumbo methanol plants.     

Solution phase synthesis of esters within a micro reactor

A range of techniques are demonstrated for the solution phase synthesis of esters within an EOF-based borosilicate glass micro reactor, including the use of mixed anhydrides and the in situ preparation of acyl halides.     

Continuous production of lactic acid from glucose and lactose in a cell-recycle reactor

Growth and lactic acid production ofLactobacillus delbreuckii were compared using glucose and lactose as carbon sources. A continuous-flow stirred-tank fermenter was coupled with a cross-flow filtration unit to permit operation at high-cell concentrations. At steady state, yeast extract requirements for lactic-acid production were lower when glucose was used as a substrate than with lactose fermentation. Once steady state was obtained, with glucose feed, it was possible to lower the yeast extract concentration without affecting biomass concentration and lactic acid production. The lacticacid concentration that inhibited cell growth and lactic acid production was found to depend on the choice of a carbon substrate.