Experimental Study on Gasification of Banknote Waste: Effects of Torrefaction Pre-Treatment and Co-Gasification on Producer Gas Composition

There is approximately 500,000 tonnes of potential end-of-life banknote waste worldwide, which is increasing by 2-3% per year. This waste consists of cotton and polymer-based banknotes printed on substrates whose raw materials are cotton and polypropylene, respectively. The vast majority of banknotes in circulation are cotton-based banknotes. End-of-life cotton banknotes, which are lignocellulosic biomass, are generally disposed of by landfill and incineration. Studies to reduce the environmental impact of these wastes to find more effective ways of using them is becoming increasingly important. Syngas, which can be used for the production of electricity, energy and chemicals is obtained by gasification of end-of-life cotton banknotes. In this study, DSC and FTIR analysis were performed as part of the characterization tests of the cotton-based banknote sample. As a result of the analysis, the sample was found to have characteristics similar to those of cotton. Within the scope of the investigation of thermal decomposition kinetics, activation energies were calculated as 134-171 kJ/mol by the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods. Experiments were performed in a fluidized-bed reactor at 800°C with an inlet H2O/O2 ratio of 25. The content of the producer gas formed during gasification was examined according to the maximum mole fraction achieved. In order to facilitate handling, storage and transportation and to improve fuel quality, the effect of torrefaction pre-treatment on the producer gas content was studied by conducting torrefaction to the cotton-based banknote sample at 250°C for 10 min. To overcome the disadvantages of plastic gasification in terms of operational sustainability, the cotton and polymer-based banknote samples were co-gasified. With the torrefaction pre-treatment, the mole fractions of H2, CO and CH4 increased, while the mole fraction of CO2 decreased. This finding revealed the effects of Boudouard, hydrogasification, water-gas and steam reformation reactions. With the co-gasification of cotton and polymer-based banknote samples, H2, CO and CO2 mole fractions decreased while CH4 mole fraction increased. This result showed that as the proportion of polymer-based banknote samples in the feedstock increased, the conversion efficiency decreased and the hydrogasification reaction became dominant.