TGA-FTIR study on the thermal decomposition of tea waste

Abstract

Tea is the dried and processed leaves of plant species (Camellia sinensis) and after water, it is the most widely consumed beverage in the world. Today, Turkey is a tea powerhouse on both the production and consumption and more than 200.000 tons of black tea is consumed in Turkey annually. Therefore, considerable waste is generated from this extremely popular beverage. The utilization of tea waste is important because of reducing this waste, using alternative energy sources and protecting environment. Pyrolysis can be described as the thermal decomposition of the organic components and tea waste can be converted into liquid, solid and gaseous products via pyrolysis to provide an energy resource or to produce certain chemicals. Thermogravimetric analysis is a useful tool to evaluate pyrolysis which is a very complex process since it provides precise measurement depending on temperature and other experimental conditions. In this study, the thermal decomposition of tea waste was studied by using thermogravimetric analyzer coupled with Fourier infrared spectrometer (TGA-FTIR). Thermogravimetric analysis of tea was carried out at four different heating rates of 5, 10, 15 and 20 °C/min from 25°C to 1000°C under nitrogen atmosphere. The results indicated that tea waste was decomposed in the temperature range of 175-550°C. The kinetic parameters, such as activation energy, pre-exponential factor and reaction order were determined using different kinetic models; namely Coast-Redfern, Friedman, Kissinger, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose models. Furthermore, the main gases released during the pyrolysis of tea waste were determined by means of TGA-FTIR.