Various methods of physical, chemical and combined physicochemical pre-treatments for lignocellulosic biomass waste valorisation to value-added feedstock/solid fuels for downstream processes in chemical industries have been reviewed. The relevant literature was scrutinized for lignocellulosic waste applicability in advanced thermochemical treatments for either energy or liquid fuels. By altering the overall naturally occurring bio-polymeric matrix of lignocellulosic biomass waste, individual components such as cellulose, hemicellulose and lignin can be accessed for numerous downstream processes such as pyrolysis, gasification and catalytic upgrading to value-added products such as low carbon energy. Assessing the appropriate lignocellulosic pre-treatment technology is critical to suit the downstream process of both small- and large-scale operations. The cost to operate the process (temperature, pressure or energy constraints), the physical and chemical structure of the feedstock after pre-treatment (decomposition/degradation, removal of inorganic components or organic solubilization) or the ability to scale up the pre-treating process must be considered so that the true value in the use of bio-renewable waste can be revealed.

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.

Leaching barley straw has been found to eliminate reactor slagging and fluidised bed agglomeration under continuous gasification.