Abstract
Most pyrolysis reactors require small sizes of biomass particles to achieve high-quality products. Moreover, understanding the usefulness of high-pressure systems in pyrolysis is important, given the operational challenges they exhibit specific to various biomass materials. To actualize these aspects, the authors first checked previous reviews involving pyrolysis on different biomass and different conditions/situations with their respective objectives and subsections. From these already existing reviews, the team found that there has not been much emphasis on high-pressure fast pyrolysis and its potential in biomass conversion, showing that it is a novel direction in the pyrolysis technology development. Therefore, this review aims to shed more light on high-pressure fast pyrolysis, drawing from (a) classification of pyrolysis; (b) reactors used in fast pyrolysis; (c) heat transfer in pyrolysis feedstock; (d) fast pyrolysis parameters; (e) properties/yields of fast pyrolysis products; (f) high pressure on pyrolysis process; (g) catalyst types and their application; and (h) problems to overcome in the pyrolysis process. This review increases the understanding regarding high-pressure fast pyrolysis. An attempt has been made to demonstrate how high-pressure fast pyrolysis can bring about high-quality biomass conversion into new products. It has been shown that fluidized bed (bubbling and circulating) reactors are most suitable and profitable in terms of product yield. The high-pressure, especially combined with the fast-heating rate, may be more efficient and beneficial than working under ambient pressure. However, the challenges of pyrolysis on a technical scale appear to be associated with obtaining high product quality and yield. The direction of future work should focus on the design of high-pressure process reactors and material types that might have greater biomass promise, as well understanding the impact of pyrolysis technology on the various output products, especially those with lower energy demands. We propose that the increase of process pressure and biomass particle size decrease should be considered as variables for optimization.
Highlights
Energy demand concerns and environmental problems have increased the global attention on renewable energy pathways to replace coal, oil, and natural gas [1]
The objective of this review is to throw more light on high-pressure fast pyrolysis, drawing from (a) classification of pyrolysis; (b) reactors used in fast pyrolysis; Energies 2021, 14, 5426 (c) heat transfer in pyrolysis feedstock; (d) fast pyrolysis parameters; (e) properties/yields of fast pyrolysis products; (f) high pressure on pyrolysis process; (g) catalyst types and their application; and (h) problems to overcome in the pyrolysis process
The quantity and quality of biochar derived from the fast pyrolysis process depend on the reactor type, feedstock, and temperature of pyrolysis, which have a considerable effect on product composition/yield [76,77,78,79,80]
Summary
Energy demand concerns and environmental problems have increased the global attention on renewable energy pathways to replace coal, oil, and natural gas [1]. To actualize better product yield, for instance, such applications have aimed to maximize energy transfer and mass concerns This is largely because many of the reactors, like those involved in a high degree of heat exchange given by exothermic reactions, have to avoid catalyst deactivation to obtain strong performance [12]. It is important to note that some conducted reviews have looked at systematic approaches for mapping biomass resources to conversion pathways, forming the basis for biomass valuation and informing when biomass pre-processing is needed to ensure feedstocks are conversion-ready [17] These reviews have considered the fundamental process mechanisms of slow pyrolysis and hydrothermal carbonization processes by identifying research needs and summarizing the characteristics of products as a useful potential for industrial applications [18]. (c) heat transfer in pyrolysis feedstock; (d) fast pyrolysis parameters; (e) properties/yields of fast pyrolysis products; (f) high pressure on pyrolysis process; (g) catalyst types and their application; and (h) problems to overcome in the pyrolysis process
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