Hanns J. Ederer

Ionic reactions and pyrolysis of glycerol as competing reaction pathways in near- and supercritical water

Abstract Experimental results of the decomposition of glycerol in near- and supercritical water are presented considering measurements in the temperature range of 622–748 K, at pressures of 25, 35, or 45 MPa, reaction times from 32 to 165 s, and different initial concentrations. The reaction was carried out in a tubular reactor and a conversion between 0.4 and 31% was observed. The main products of the glycerol degradation are methanol, acetaldehyde, propionaldehyde, acrolein, allyl alcohol, ethanol, formaldehyde, carbon monoxide, carbon dioxide, and hydrogen. The results are compared with the studies of other working groups. The non-Arrhenius behavior of the overall degradation, as well as the pressure dependence of the reaction rate, and furthermore, the product distribution indicates the occurrence of two competing reaction pathways. One pathway consists of ionic reaction steps, which are preferred at higher pressures and/or lower temperatures. The second reaction pathway is a free radical degradation and dominates at lower pressures and/or higher temperatures. For reaction modeling, both mechanisms, the ionic and the free radical reaction network are compiled into one reaction model. The computer software package chemkin was used for the model calculations. The reaction model and the kinetic parameters were optimized in order to describe the experimental results for glycerol and the main products at 450 bar and all temperatures. This reaction model, consisting of the ionic and the free radical sub-mechanism satisfactorily describes the complex reaction at 450 bar.

Fractionation of polymers by gel permeation chromatography: An experimental and theoretical approach

Summary The mechanism of gel permeation chromatography has been studied in a series of experiments performed on separation matrices of controlled pore glass with known pore structure and narrow pore size distribution, and using dextran fractions with accurately determined molecular weights and very narrow molecular weight distribution. Molecular weight calibration of the columns and effects of experimental variables on the shape of the elution peak and the peak broadening function were investigated, and the distribution and transport of polymer molecules between the mobile phase and the stationary phase within the pores of the separation material were discussed. An improved stochastic model for molecular weight calibration of separation matrices with cylindrical pores is developed as a function of the pore diameter.

Size Exclusion Chromatography (SEC) of Complex Polymers - Generalized Analytical Corrections for Imperfect Resolution

Abstract Herein is reported generalized analytical solutions which permit correction for imperfect resolution when the molecular weight calibration curve is nonlinear and the variance of single-species chromatograms changes significantly with molecular size of the polymer solute. Two kinds of generalized analytical solutions have been obtained. One is a solution of Tungs integral equation for the corrected chromatogram or the molecular weight distribution and the other is a solution for the corrected molecular weight averages of the whole polymer. Also discussed is the use of local corrections for imperfect resolution across the chromatogram with detectors such as the low angle laser light scattering spectrophotometer (LALLS) when used with micro and macropackings.

Oligomer formation in the chemical degradation of dextran

SummaryThe production of oligomers — to a degree of polymerization 5 — during acid hydrolization of polymer dextrans was estimated quantitatively by a combined aqueous SEC and adsorption separation. It was found that the molar concentrations of the oligomers were higher for those with lower DP. This experimental result is in agreement with a degradation model, in which the molecular weight decreases with the power of 2/3 versus time, which has been proposed earlier.

Mass transfer coefficients from pendant water drop measurements in compressed carbon dioxide

Abstract Mass transfer coefficients were determined in the two-phase system of water/compressed carbon dioxide at three temperatures of 297, 313 and 335 K, and in the pressure range of 6–25 MPa. Mutual Mass transfer of the two components, water and carbon dioxide was investigated in the binary system, and extraction of phenol from an aqueous droplet by carbon dioxide was studied in a ternary system. In all systems a pendant water drop was formed at the tip of a capillary and was exposed to the quiescent surrounding carbon dioxide for a definite time. To obtain mass transfer coefficients from experimental data, such as drop volume and phenol concentration as a function of contact time, a model was used that divides the transport process into three steps: transport towards the interface, passage through the interface, transport straight away from the interface. Depending on the particular system, only one or two of these steps were considered to have a rate-determining function.

Kinetic Studies of Methanol Oxidation in Supercritical Water and Carbon Dioxide

As is shown by working groups all over the world, supercritical water oxidation is a promising technology for the complete oxidation of aqueous hazardous waste from different sources, such as aqueous waste from the pharmaceutical and chemical industries [1, 2]. The function of the reaction medium supercritical water during oxidation, howver, is not well understood.

Modelling of Polymer Gel Formation and Gel Reactions with Monte Carlo Methods for 3-dimensional Networks

The thermal treatment of poly-(p-methyl-styrene) was investigated experimentally. In contrast to polystyrene, gels are formed and decomposed again, depending on temperature. Based on the experimental results a reaction model for polymer decomposition, polymer gel formation and polymer gel degradation was developed. A Monte Carlo simulation program using methods from percolation theory is presented which covers thermal gel formation, gel formation caused by radiation, gel formation during polymerization, thermal, mechanical and ultrasonic decomposition of polymer gels and highly branched polymers.