A review on lignin pyrolysis: pyrolytic behavior, mechanism, and relevant upgrading for improving process efficiency

Abstract

Lignin is a promising alternative to traditional fossil resources for producing biofuels due to its aromaticity and renewability. Pyrolysis is an efficient technology to convert lignin to valuable chemicals, which is beneficial for improving lignin valorization. In this review, pyrolytic behaviors of various lignin were included, as well as the pyrolytic mechanism consisting of initial, primary, and charring stages were also introduced. Several parallel reactions, such as demethoxylation, demethylation, decarboxylation, and decarbonylation of lignin side chains to form light gases, major lignin structure decomposition to generate phenolic compounds, and polymerization of active lignin intermediates to yield char, can be observed through the whole pyrolysis process. Several parameters, such as pyrolytic temperature, time, lignin type, and functional groups (hydroxyl, methoxy), were also investigated to figure out their effects on lignin pyrolysis. On the other hand, zeolite-driven lignin catalytic pyrolysis and lignin co-pyrolysis with other hydrogen-rich co-feedings were also introduced for improving process efficiency to produce more aromatic hydrocarbons (AHs). During the pyrolysis process, phenolic compounds and/or AHs can be produced, showing promising applications in biochemical intermediates and biofuel additives. Finally, some challenges and future perspectives for lignin pyrolysis have been discussed.

Characterization and Comparison of Some Kraft Lignins Isolated from Different Sources

“…During the VM analyses at 250 • C, lignin structures broke down while evaporating the small molecular weight structures [19]. For this reason, the volatile matter contents strongly affected the thermal behavior [6]. Thus, a high volatile material ratio may limit fiber spinning and result in deficiencies in the carbon fiber production [19].…”

“…In addition, most kraft lignin is still burned to recover its inorganic components, while producing thermal energy during the process [5]. Although burning kraft lignin is important in terms of meeting the thermal energy needs of paper mills, approximately 90% of lignin is burned inefficiently, while only 2% is utilized effectively [6]. For this reason, the importance of studies on lignin isolation and characterization is growing, with research aiming to increase both the potential uses and the effective use of lignin.…”

“…As the pH of black liquor falls below 10.5, the phenolic -OH groups in lignin absorb a large number of protons. As a result, carboxylic acid groups indicating the presence of degraded hemicelluloses, which are absorbed onto lignin in pulping or covalently bonded lignin with esters bonds, are protonated at lower pH values (between three and four), [6,7]. In addition to the decrease in pH value during the isolation process, the lignin properties change with acid type [13].…”

Catalytic Pyrolysis of Sawdust with Desulfurized Fly Ash for Pyrolysis Gas Upgrading

“…Compared with the water yield of SD pyrolysis (14 wt.%, daf), CaSO 3 accelerated water formation during SD pyrolysis. Xinyu Lu et al [ 27 ] reported that Ca(OH) 2 contributed markedly to the formation of pyrolysis water during lignocellulose pyrolysis. Therefore, this result further suggested that Ca(OH) 2 , as the second-most prevalent component in DFA, also promoted the SD decomposition to improve pyrolytic water yield during DFA/SD pyrolysis.…”

TGA-FTIR Analysis of Biomass Samples Based on the Thermal Decomposition Behavior of Hemicellulose, Cellulose, and Lignin

“…Also, the highly aromatic structure of lignin, which contains aromatic rings, makes it more thermally stable than the aliphatic bonds found in cellulose and hemicellulose. Since it is more difficult to break down these aromatic rings during pyrolysis, lignin produces fewer amounts of condensable volatiles, and hence the bio-oil yield is the lowest among the other constituents [43,71].…”