Preliminary kinetics study of 5-nonanol intramolecular dehydration over an acidic macroporous ion-exchange resin

Abstract

The strong dependence on fossil fuels in our society is currently regarded as one of the most difficult problems to tackle in this era of huge energy demands. Possible solutions to replace these resources are being studied and one of them are biofuels. In order to obtain these products, a great reaction pathway must be carried out, where biomass-derived alkanoic acids coming from cellulose, hemicellulose, tall oil and vegetable oil, are converted into several valuable chemicals and motor fuel components. The present work focusses on a certain reaction of this pathway, consisting of a 5-nonanol dehydration into 3-nonene and 4-nonene. A kinetic study has been carried out throughout experimental work in the laboratory. The main aim of this project is to find a kinetic equation that explains satisfactorily 5-nonanol dehydration over certain experimental conditions. Amberlyst-45 is used as catalyst because previous works confirm great results obtained with it. To fulfill the objective, an extensive bibliographical research has been done to find the most common formulism to describe this type of reaction. Consequently, with all the information gathered, a total of 40 different expressions have been tested. Experimental data has been fitted to all of them. Selection of the best expression is based on four different parameters: Sum of square errors, residual distribution, evolution of the kinetic constant with temperature and activation energy. Two models provide good results in accordance with the parameters previously quoted. In the first one, based on Langmuir-Hinshelwood-Hougen-Watson formulism, an adsorbed molecule of 5-nonanol reacts to yield 3-nonene, 4-nonene and water. The equilibrium constant is considered to have a high value, which simplifies the final expression. The second model is based on Eley-Rideal formulism. Now, an adsorbed molecule of 5-nonanol reacts with another one in the bulk phase to yield 3-nonene, 4-nonene and water, which is released directly to solution. The equilibrium constant is considered to have a high value, as in the first model, and the adsorption term is simplified by suppressing the part corresponding to the desorption of 3-nonene and 4-nonene. In both cases, reaction on the catalyst surface is considered as the rate controlling step of the process