Augmented Leaching Pretreatments for Forest Wood Waste and Their Effect on Ash Composition and the Lignocellulosic Network

Abstract

By augmenting conventional leaching technologies for the removal of ash constituents from lignocellulosic waste residues, a cleaner and energy efficient solution can be provided for critical industrial problems such as biomass feeding, defluidization, and reactor corrosion. It has been found that not only are inorganic constituents (ash) effectively removed by coupling a physicochemical technology with conventional leaching but also the intermolecular interactions within the lignocellulosic matrix can be modified, as shown by a variable crystallinity index (powder X-ray diffraction) without the loss of physical bonding (Fourier-transform infrared spectroscopy). Ultimately, this allowed for a greater thermochemical transformation of cellulose, hemicellulose, and lignin for all technologies used: conventional leaching, indirect/directed ultrasound, and microwave irradiation. However, the use of directed ultrasound was found to be the standout, energy efficient technology (8.6 kJ/g) to radically improve the thermochemical transformation of wood waste, especially in the reduction of fixed carbon at high temperatures. It was also found to be efficient at removing vital eutectic mixture causing elements, including Si, which is known to be notoriously difficult to remove via leaching. In comparison, hot plate leaching and microwave irradiation use 39 and 116 times more energy, respectively. The integration of this technology into the energy production sector will prove vital in the future due to its scalability, as compared with microwave alternatives, which are currently not suitable for large scale operations. Additionally, the residence time required for directed ultrasound was found to be negligible as compared to the various other physicochemical techniques, 0.1 h opposed to 4 h.