The Study of Ethylene Oxide Reactions by Heat Flow Calorimetry

Ethylene oxide is a colourless gas condensing at low temperatures to a mobile liquid. It is a highly flammable and toxic material. Ethylene oxide contains an epoxide ring that is under an immense strain and is thus characterised by great reactivity. Ethylene oxide is easily added to compounds with an active hydrogen atom and the primary reaction product is always a glycol derivative with a reactive hydroxyl group. The product of such a reaction is itself an alkoxide anion and can thus react further with another molecule of ethylene oxide. It is for this property, that is, its ability to form a hydrophilic chain, that it is used in a wide number of products including surfactants. The aim of the programme was to study novel and industrial reactions of ethylene oxide and acquire thermodynamic and kinetic data using heat flow calorimetry techniques. The reactions studied include both novel and commercial preparations with the emphasis on fatty substrate based non-ionic surfactant products. An appraisal of thermometric techniques was supported by a series of experiments on novel ethoxylation reactions using a conventional, commercial reaction calorimeter running at atmospheric pressure and a previously developed reflux calorimeter. Both were deemed inadequate for the study, due primarily to losses of the ethylene oxide. A new calorimetric system, which could operate under pressure was required. The development of a pressurised heat flow calorimeter (PHFC) with an integral controlled dosing system for use with hazardous (flammable and toxic) materials in order to study normal, desired commercial ethoxylation reaction systems is described. Thermodynamic and kinetic data have been obtained for ethoxylation reactions using the PHFC. The major findings are that the heat produced by the addition of ethylene oxide to a fatty substrate is 100-145 kJ/mol of ethylene oxide added. The heat release in such reactions is dependent upon the physical and chemical nature of the fatty substrate. The findings are in general agreement with theoretical approaches to the acquisition of thermodynamic data, proposed reaction mechanisms and kinetic formulae. The level of accumulation of heat/reactants under the conditions studied were typically under 10% at any one time and it is suggested that current operating procedures are safe. The possible use of this data in a hazard assessment strategy and scale up procedures is described. The direction of suggested future work is also detailed.