Organic Degradation Products Research Articles

Thermal Degradation Products of Steel Protective Paints

Organic degradation and emission products from painted steel were studied in laboratory experiments. Steel plates coated with paints for the ship building industry were heated with a liquid gas flame to 350°C. Emitted products were collected by different adsorption tubes, bubbler absorbers, and filters, for identification by gas chromatography, liquid chromatography, and mass spectrometry. The main degradation products typically originated from the binders in the paints, i.e., bisphenol-A from epoxies, phthalic anhydride from alkyds, butyraldehyde from polyvinylbutyral. Small molecular aldehydes, acids, and solvents were also detected. For sampling on-site an XAD-2 tube with a pre-connected glass fiber filter and a chemosorbent tube for aldehydes is recommended.

Modelling Studies of the Sorption of Uranium and Plutonium in the far Field of A Nuclear Waste Repository

ABSTRACTModels of the transport of sorbing radioelements through geological materials have been developed. These models couple a surface-complexation model of sorption processes with transport simulations in the CHEQMATE code. The chemical model has been shown to reproduce trends observed in batch sorption experiments. This approach may ultimately be used to investigate possible limitations to the use of models using simple Kds in repository safety-assessments. The main aim of the study reported in this paper is to increase confidence in the use of the coupled models. Simulations of through-diffusion experiments of uranium with London clay and plutonium with sandstone are presented. In both cases gluconate is present, as a simulant of organic degradation products of cellulose likely to be present in a low- or intermediate-level waste repository.

Studies of the Effects of Degradation Products on the Sorption of Tin and Radium

ABSTRACTThe effects on sorption on geological media caused by the presence of materials derived from a cementitious repository have been studied. This work includes an investigation of the influence of cellulosic degradation products on the sorption of tin and radium on London clay and Caithness flagstones and the sorption of radium as a function of calcium concentration.Experimental conditions were chosen to simulate those expected close to a cementitious repository (pH=l1) and at the edge of the zone of migration of the calcium plume (pH=8). Work was carried out, (i) under baseline conditions in the absence of organic materials; (ii) with gluconate, acting as a well-characterized organic degradation product simulant; (iii) with authentic cellulosic degradation products.This investigation has shown that the sorption of tin can be affected by the presence of cellulosic degradation products whereas the sorption of radium is little affected. The sorptive behaviour of radium is however strongly influenced by the calcium concentration.

An analytical investigation of the thermal degradation of a cation-exchange resin — part 2

In part 1 of this study the thermal degradation of an ion-exchange resin was followed by laser microprobe mass analysis (LAMMA), which revealed the processes of desulphonation and polymer chain degradation. Also, an initial gas chromatography/mass spectrometry (GC/MS) analysis identified 1,3-diphenylpropane as being a major degradation product. Unsaturated organic degradation products were not particularly evident. In this article the identification by GC/MS analysis of the organic thermal degradation products of the same ion-exchange resin are presented, permitting the LAMMA technique to be used alone in order to follow the resin's degradation processes. All the information obtained has led to the proposal of an approximate thermal degradation mechanism for this resin, which is presented here. The resin is a sulphonated copolymer of polystyrene and divinylbenzene. The organic degradation products are formed from pyrolysis at 300 °C over 24 h. During pyrolysis the resin is in an aqueous environment.

An analytical investigation of the thermal degradation of a cation-exchange resin — part 1

In this first part of a two-part investigation the preliminary results of the thermal degradation at 300 °C in an aqueous milieu of a cation-exchange resin are presented. The resin is a sulphonated copolymer of styrene (92%) and divinylbenzene. The desulphonation and degradation of the resin was followed by the analytical techniques of laser microprobe mass analysis (LAMMA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Sulphuric acid attack on the metallic surface of the pyrolysis crucible was verified and the identification of the resultant inorganic products was performed by LAMMA and Fourier transform infrared spectroscopy. Nuclear magnetic resonance spectroscopy indicated that few or no unsaturated organic degradation products were formed. GC/MS identified a predominant degradation product as 1,3-diphenylpropane. A Py-GC/MS study on resin residues with respect to varying pyrolysis temperatures and times shows that the formation of organic sulphur compounds are favoured at higher temperatures. This implies that some form of reduction occurs during thermal degradation.

Modelling the Behaviour of Organic Degradation Products

ABSTRACTResults are presented from recent studies at Harwell which show that the degradation products which are formed when certain organic waste materials are exposed to the alkaline conditions typical of a cementitious environment, can enhance the solubility of plutonium, even at pH values as high as 12, by significant factors. Characterisation of the degradation products has been undertaken but the solubility enhancement does not appear to be related to the concentration of any of the major organic species that have been identified in the solutions. While it has not been possible to identify by analysis the organic ligand responsible for the increased solubility of plutonium, the behaviour of D-Saccharic acid does approach the behaviour of the degradation products. The PHREEQE code has been used to simulate the solubility of plutonium in the presence of D-Saccharic acid and other model degradation products, in order to explain the solubility enhancement. The extrapolation of the experimental conditions to the repository is the major objective, but in this work the ability of a model to predict the behaviour of plutonium over a range of experimental conditions has been tested.

Anodic oxidation of phenolics found in coal conversion effluents

AbstractSolutions of phenol, o‐cresol, p‐cresol, 2,3‐xylcnol, 3,4‐xylenol, resorcinol, and catechol at concentrations below I g/L were oxidized at constant current on a packed bed lead dioxide electrode with electrolyte recirculation. The effects of applied current and initial concentration on the extent of oxidation with time were explored. The observed ranking in ease of oxidation was phenol > 2,3‐xylenol > resorcinol > p‐cresol > 3,4‐xylenol > o‐cresol. Although the phenolics were largely destroyed, organic degradation products of the quinone and hydroquinone type remained in solution. A mixture of five monohydric phenols showed 96% destruction of phenolics, a 50% reduction in B.O.D. but a reduction in total organic carbon of only 22%.

High‐temperature pyrolysis of poly(vinyl chloride): Gas chromatographic‐mass spectrometric analysis of the pyrolysis products from PVC resin and plastisols

AbstractA pyrolysis–gas chromatographic–mass spectrometric technique for analyzing the pyrolysis products from polymers in an inert atmosphere is described. Initial studies encompassing the pyrolysis of poly(vinyl chloride) homopolymer and a series of PVC plastisols (based on o‐phthalate esters) have provided a complete qualitative and semi‐quantitative analysis of the pyrolysis products from these materials. PVC resin yields a series of aliphatic and aromatic hydrocarbons when pyrolyzed at 600°C; the amount of aromatic products is greater than the amount of aliphatic products. Benzene is the major organic degradation product. A typical PVC plastisol [PVC/o‐dioctyl phthalate (100/60)] yields, upon pyrolysis, products that are characteristic of both the PVC matrix and the phthalate plasticizer. The pyrolysis products from the plasticizer dilute those from the PVC portion of the plastisol and are, in turn, the major degradation products. There are no degradation products resulting from an interaction of the PVC with the plastisol. The pyrograms resulting from pyrolysis of the various plastisols of PVC can be used for purposes of “fingerprinting.” Identification of the major peaks in a typical plastisol pyrogram provides information leading to a precise identification of the plasticizer. The pyrolysis data from this study were related to a special case of flammability and toxicity.