Advancements in sustainable thermochemical conversion of agricultural crop residues: A systematic review of technical progress, applications, perspectives, and challenges

Agricultural crop residues are the lignocellulosic biomass left in the field after harvesting valuable crop parts. These pose a significant concern due to the waste generated annually, burdening management and contributing to pollution. Numerous studies carried out over decades have demonstrated some effective utilization through thermochemical conversion as a potential feedstock, there is not a proper account of their trends. This systematic review addresses a critical gap in the literature by analyzing the sustainable management of crop residues thermochemically, offering insights into research trends, technologies, and future directions for their utilization as biofuel and bioactive value-added-product applications, that has been largely overlooked in previous narrative reviews. Studies for review were searched on web of science, scopus, and google scholar through a carefully developed search syntax and backward snowball methods. Total 343 papers published in past 23 year matched the study inclusion criteria were selected and meaningful outcomes from meticulous analysis of these studies have been extracted. Research publications show exponential growth, primarily focused on laboratory-based experiments. The most studied process was pyrolysis, and the product was biochar. There has been significant progress in process optimization, integration, and product diversification, paving the way for diverse applications. Recent trends indicate a shift from conventional pyrolysis and gasification towards sustainability, circular economy, efficiency enhancements, and novel applications, reflecting a broader commitment to environmental stewardship and resource maximization. Additionally, the challenges linked with recent innovations are discussed, along with recommendations for future research endeavors concerning these systems.