Publications by Albert Renken | EPFL Graph Search

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An interesting possibility for the use of lactoserum in human nutrition is the hydrolysis of lactose to glucose and galactose, sugars which exhibit a better digestibility, a higher solubility, and which have a greater sweetening power than lactose. The hydrolysis is catalyzed by an enzyme, the β-galactosidase which, due to its high price, must be used continuously, preferentially in immobilized form. The enzyme used for these studies has been immobilized on silica gel precoated with chitosan. When whole whe

Results concerning the coupling of the steam reforming and total oxidn. of methanol in a two-passage reactor are presented. A com. available copper-based catalyst is used for the steam reforming. For the total oxidn., a highly active cobalt oxide catalyst was developed. Both catalysts are used in form of thin layers immobilized on the wall of the microchannels. Reactor design and operating conditions are based on kinetic models developed under isothermal conditions in microstructured reactors. For the oxidn

An interesting possibility for the use of lactoserum in human nutrition is the hydrolysis of lactose to glucose and galactose, sugars which exhibit a better digestibility, a higher solubility, and which have a greater sweetening power than lactose. The hydrolysis is catalyzed by an enzyme, the b-galactosidase which, due to its high price, must be used continuously, preferentially in immobilized form. The enzyme used for these studies has been immobilized on silica gel precoated with chitosan. When whole whe

Material and temp. instabilities in autothermal reactors, e.g. catalyst temp. instabilities and steep radial and axial temp. profiles, and difficulty in isolation of intermediate products, are resolved by periodic operation of the reactor. Using the oxidn. of propylene over Pt gauze as an example, it was shown that operation at high frequency within the temp.-conversion hysteresis allows the reactor to operate in a pseudostationary mode at one of the stable operating points. Increasing the mass capacity or

A novel reactor based on a bubble column staged by structured catalytic layers with integrated cross flow micro-heat-exchangers (HEX) was designed and tested in the solvent free hydrogenation of 2-methyl-3-butyn-2-ol (MBY) aiming on process intensification ...

Enzymic hydrolyses of naturally occurring protein sources represent complex reactions at a molecular level because of the specificity pattern of proteases and the composition of the substrates involved. In addition, rather global criteria are in practical use for describing the extent of protein hydrolysis. Therefore, mechanistically based kinetic modelling may not be applicable under these circumstances. For practical purposes it is often sufficient to use a descriptive mathematical model, which leads to a

Many chem. reactions, like the dehydrogenation of gaseous methanol to formaldehyde, require fast heating and cooling of the gases to control precisely the residence time at the reaction temp. (on the order of hundreds of ms) to minimize consecutive reactions. For these applications, microsystems are of great interest thanks to their characteristic high surface- to-vol. ratio and low thermal inertia. Heater and cooler units were developed with compatible micromachining technologies in view of a future integr

V substituted phosphomolybdic acids could hydroxylate benzene with nearly 100% selectivity at appreciable conversion levels in the presence of oxidizing agents like H2O2 and AcOOH. There appears to be a correlation, for the liq. phase, between phenol yield and its rate of formation with V content in the phosphomolybdic acid. Unfortunately, these materials do not show the same activity in gas-phase with N2O as oxidant. Therefore, the high acidity of these solids is not involved in the reaction pathway. [on S

Transient expts. were applied to the study of the adsorbed CO intermediate, (CO)a, formed during CO2 methanation on 2 wt.% Ru/TiO2 catalyst at 383 K. Step-up expts. showed that the (CO)a formation steps are inhibited by H2O and enhanced by H2. Step-down expts. showed that the (CO)a hydrogenation is not influenced by the partial pressure of water. Based on the fact that water inhibits the overall CO2 methanation, it was deduced that the rate limiting process in the overall reaction is (CO)a formation. [on Sc

Microstructured reactors (MSR) with characteristic dimensions below 100 μm are warranted to maintain close to isothermal conditions when carrying out quasi-instantaneous highly exothermic reactions. Unfortunately, such small dimensions increase the risk of clogging, create high pressure drop and are costly to number-up. The multi-injection (MI) MSR, where one of the reactants is added stepwise along the reactor length, allows working with larger dimensions (diameter >500 μm) while maintaining good temperatu

Pd nanoparticles (2 nm) stabilized in the micelle core of poly(ethylene oxide)-block-poly(2-vinylpyridine) were studied in partial hydrogenation of 2-butyne-1,4-diol. Both unsupported micelles (0.6 kg Pd/m3) and supported ones on g-Al2O3 (0.042% Pd) showed ...

Solid epoxy resins are produced by catalyzed reactions of a low-mol.-wt. liq. resin (RBL) with bisphenol A (BPA). These reactions lead to solid epoxy resins that have many uses. The chain lengthening step (advancement reaction) is based on the reaction of the epoxy functional group with the phenolic hydroxyl group and leads to the formation of a secondary hydroxyl group. These secondary hydroxyl groups can react with epoxy groups to form branched mols. The aim of the present study is to develop a kinetic mo

Reactor operation with immobilized enzymes in fixed bed arrangement is often impaired due to the presence of finely divided solid matter, adsorbing substances or gas. The fluidized bed reactor would be applied in such cases owing to a limited pressure drop, a controlled voidage, and the avoidance of perforated plates for catalyst retention. Since enzymic reactions are often slow processes, catalysts of high external surface area should be provided together with sufficient time. However, classical fluidized

The title reactor, of simple construction and suppressing segregation and overheating, consists of a tube filled with static mixing elements, sepd. into a 1st segment which is sepd. by a recirculating pump from the 2nd and 3rd segments, which form a piston-flow reactor. Thus, the polymn. of styrene in such a reactor with the 1st segment and recycle loop at 158 Deg and recycle ratio 10 gave a 60% conversion to polystyrene [9003-53-6] with no.-av. mol. wt. 93,000, polydispersity 1.9, viscosity of the polymn.

The kinetics of the adsorption of human serum albumin (HSA) onto spherical resin beads (Blue Sepharose CL-6B) in a closed stirred tank have been investigated. The differential equation with appropriate boundary conditions at the grain outer surface may be solved numerically or to various degrees of approxn. Using the Laplace transform technique to solve the equation of interest, we are able to obtain the exact soln. to the problem, in the Laplace domain. We assume that equil. is described by a linear absorp

Periodic operation was applied to the CO2 methanation reaction at 383 K on 2% Ru/TiO2. A continuous feed recycle reactor combined with a diffuse reflectance infrared cell and a mass spectrometer allowed to follow simultaneously the gas phase CO2 and CH4 as well as the adsorbed species (CO)a and (formate)a. Experiments consisting of periodic variations of CO2 in the hydrogen feed showed response curves with maxima/minima shifted in time in the sequence CO2, (formate)a --> (CO)a --> CH4. Similar delays measur

A novel concept of a recycle loop reactor is developed with structured filamentous catalysts integrated as trays in a staged bubble column. The reactor can be operated in batch or continuous mode. Woven fabrics of activated carbon fibers (ACF) were used as support for the Pd catalyst. The loop reactor was tested in the 2-butyne-1,4-diol hydrogenation showing selectivity up to 97% towards 2-butene-1,4-diol at conversions up to 80%. The reactor behavior was described quant. assuming an ideally mixed reactor a

Though microreactors provide high heat transfer rates, temperature profiles are formed in case of fast and highly exothermic reactions. A method based on non-intrusive infrared thermometry has been developed to track these profiles quantitatively with a resolution of 250 data points/cm(2) and a precision of 1 degrees C. By placing the microreactor at a pressure of 10(-2) mbar, convective heat losses are efficiently suppressed which assures well defined boundaries and reproducible results. The temperature pr

The pptn. of barium sulfate from a basic EDTA complex upon addn. of a small vol. of acid in a stirred-tank reactor was used as a model reaction to study the local state of micromixing. Limitations and modifications of this reaction are presented, and its application on an industrial pilot scale is realized. A higher reaction rate is used in order to decrease the reaction time by using different concns. of reactants which modify the stability of the ppt. A study of this stability is presented. [on SciFinder

The catalytic cracking of methane over nickel gauze is proposed as an attractive alternative for the prodn. of CO-free hydrogen. The catalyst deactivates due to intensive coke deposition. Therefore, the reactor was operated periodically with the reaction followed by the catalyst regeneration by burning of coke in oxidative atm. The optimal reaction performance was found to consist of reaction periods of 4 min followed by 4 min regeneration periods. [on SciFinder (R)]

Albert Renken

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Engineering Aspects of Fluidized Bed Reactor Operation Applied to Lactose Treatment of Whole Whey

Hydrogen production for fuel cell application in an autothermal micro-channel reactor

Engineering Aspects of Fluidized Bed Reactor Operation Applied to the Lactose Treatment of Whole Whey

Ignition and Extinction of Autothermal Reactors at Periodic Operation

A novel compact reactor for three-phase hydrogenations

Empirical Kinetic Models for Tryptic Whey-Protein Hydrolysis

Fast heating and cooling for high temperature chemical microreactors

Partial oxidation of benzene catalyzed by heteropoly compounds

Transient drift spectroscopy for the determination of the surface reaction kinetics of CO2 methanation

Intensification of highly exothermic fast reaction by multi-injection microstructured reactor

Palladium nanoparticles stabilized in block-copolymer micelles for highly selective 2-butyne-1,4-diol partial hydrogenation

Determination of kinetics models for the polyaddition of bisphenol A with an epoxide liquid resin

Development of an enzyme fluidized bed reactor equipped with static mixers: application to lactose hydrolysis in whey

Reactor for continuous polymerization in a high viscosity medium

Use of the Laplace transform technique for simple kinetic parameters evaluation. Application to the adsorption of a protein on porous beads

Periodic operation applied to kinetic studies of CO2-methanation

Loop reactor staged with structured fibrous catalytic layers for liquid-phase hydrogenations

Infrared imaging of temperature profiles in microreactors for fast and exothermic reactions

Barium sulfate precipitation as model reaction for segregation studies at pilot scale

Hydrogen production by catalytic cracking of methane over nickel gauze under periodic reactor operation