Pyrolysis of anaerobic digested residues in the presence of catalyst-sorbent bifunctional material: Pyrolysis characteristics, kinetics and evolved gas analysis

Waste to energy: Trending key challenges and current technologies in waste plastic management

Due to the 'forever' degrading nature of plastic waste, plastic waste management is often complicated. The applications of plastic are ubiquitous and inevitable in many scenarios. Current global waste plastics production is ca. 3.5 MMT per year, and with the current trend, plastic waste production will reach 25,000 MMT by 2040. However, the rapid growth in plastic manufacture and the material's inherent nature resulted in the accumulation of a vast amount of plastic garbage. The current recycling rate is <10 %, while the large volumes of discarded plastic waste cause environmental and ecological problems. Recycling rates for plastic vary widely by region and type of plastic. In some developed countries, the recycling rate for plastics is around 20-30 %, while in many developing nations, it is much lower. These statistics highlight the magnitude of the plastic waste problem and the urgent need for comprehensive strategies to manage plastic waste more effectively and reduce its impact on the environment. This review critically analyses past studies on the essential and efficient techniques for turning plastic trash into treasure. Additionally, an attempt has been made to provide a comprehensive understanding of the plastic upcycling process, the 3Rs policy, and the life-cycle assessment (LCA) of plastic conversion. The review advocates pyrolysis as one of the most promising methods of turning plastic trash into valuable chemicals. In addition, plastic waste management can be severely impacted due to uncontrollable events, such as Covid 19 pandemic. Recycling and chemical upcycling can certainly bring value to the end-of-life plastic. However, the LCA analysis indicated there is still a huge scope for innovation in chemical upcycling area compared to mechanical recycling. The formulation of policies and heightened public participation could play a pivotal role in reducing the environmental repercussions of plastic waste and facilitating a shift towards a more sustainable future.

Effect of physical and thermal pretreatment of lignocellulosic biomass on biohydrogen production by thermochemical route: A critical review

Energy demands and immense environmental degradation have extorted for production of low-carbon and carbon-neutral fuels. Abundantly available lignocellulosic biomass is second-generation feedstock which has potential to produce biofuels. Among all biofuels, biohydrogen is carbon neutral and sustainable biofuel which can be produced by thermochemical conversion routes mainly gasification. However, there are still numerous unsolved challenges related to physicochemical properties of lignocellulosic biomass. To tackle these issues, physical, chemical and thermal pretreatment methods can be employed to improve these properties and further strengthen usability of biomass for biohydrogen production. Pelletization, torrefaction and hydrothermal carbonization pretreatment have shown significant results for treating biomass and biohydrogen enhancement. This study reviews physical and thermal pretreatment and its effect on biohydrogen yield. Framework of techno-economic analysis of processes is provided for examining feasibility of required pretreatments. This sustainable approach will help to reduce emissions and promote concept of bioenergy with carbon capture and storage.

Biomass pyrolysis: A review on recent advancements and green hydrogen production

Biomass pyrolysis has recently gained increasing attention as a thermochemical conversion process for obtaining value-added products, thanks to the development of cutting-edge, innovative and cost-effective pyrolysis processes. Over time, new and novel pyrolysis techniques have emerged, and these processes can be tuned to maximize the production of high-quality hydrogen. This review examines recent advancements in biomass pyrolysis by classifying them into conventional, advanced and emerging approaches. A comprehensive overview on the recent advancements in biomass pyrolysis, highlighting the current status for industrial applications is presented. Further, the impact of each technique under different approaches on conversion of biomass for hydrogen production is evaluated. Techniques, such as inline catalytic pyrolysis, microwave pyrolysis, etc., can be employed for the sustainable production of hydrogen. Finally, the techno-economic analysis is presented to understand the viability of pyrolysis at large scale. The outlook highlights discernments into future directions, aimed to overcome the current shortcomings.

Probing the effect of Cu-SrO loading on catalyst supports (ZSM-5, Y-zeolite, activated carbon, Al2O3, and ZrO2) for aromatics production during catalytic co-pyrolysis of biomass and waste cooking oil

In this work, Cu-SrO bimetallic catalyst was synthesised and examined for catalytic co-pyrolysis of ironbark (IB) and waste cooking oil (WCO) using Py-GC/MS. The effect of catalyst supports (ZSM-5, Y-zeolite, activated carbon, Al₂O₃, and ZrO₂) on aromatic hydrocarbons yield was studied. The effect of catalyst support on the selectivity of gasoline (C8-C14), diesel (C15-C17), and heavy oil (>C20) components of bio-oil were studied. Non-catalytic co-pyrolysis of IB and WCO produced a heavy oil component of 58.7% (>C20). SrO initiated a ketonization reaction that converted carboxylic acids into new C-C bonds. The addition of Cu effectively promoted secondary cracking and aromatization reactions enhancing the hydrocarbon yield. Cu-SrO/ZSM-5 and Cu-SrO/Y-zeolite produced low acid content of 4.43% and 12.5%, respectively. Overall, the bimetallic catalyst Cu-SrO/ZSM-5 significantly increased the amount of C8-C14 compounds to 87.28% and reduced compounds over C20 to 1.19%.

Integrated system of anaerobic digestion and pyrolysis for valorization of agricultural and food waste towards circular bioeconomy: Review

Agricultural and food waste have become major issue affecting the environment and climate owing to growing population. However, such wastes have potential to produce renewable fuels which will help to meet energy demands. Numerous valorization pathways like anaerobic digestion, pyrolysis, composting and landfilling have been employed for treating such wastes. However, it requires integrated system that could utilize waste and promote circular bioeconomy. This review explores integration of anaerobic digestion and pyrolysis for treating agricultural and food waste. Proposed system examines the production of biochar and pyro-oil by pyrolysis of digestate. The use of this biochar for stabilizing anaerobic digestion process, biogas purification and soil amendment will promote the circular bioeconomy. Kinetic models and framework of techno-economic analysis of system were discussed and knowledge gaps have been identified for future research. This system will provide sustainable approach and offer carbon capture and storage in form of biochar in soil.