Radicals and molecular products from the gas-phase pyrolysis of lignin model compounds. Cinnamyl alcohol

Abstract

The experimental results on detection and identification of intermediate radicals and molecular products from gas-phase pyrolysis of cinnamyl alcohol (CnA), the simplest non-phenolic lignin model compound, over the temperature range of 400–800 °C are reported. The low temperature matrix isolation – electron paramagnetic resonance (LTMI-EPR) experiments along with the theoretical calculations, provided evidences on the generation of the intermediate carbon and oxygen centered as well as oxygen-linked, conjugated radicals. A mechanistic analysis is performed based on density functional theory to explain formation of the major products from CnA pyrolysis; cinnamaldehyde, indene, styrene, benzaldehyde, 1-propynyl benzene, and 2-propenyl benzene. The evaluated bond dissociation patterns and unimolecular decomposition pathways involve dehydrogenation, dehydration, 1,3-sigmatropic H-migration, 1,2-hydrogen shift, C—O and C—C bond cleavage processes.

Measuring biomass fast pyrolysis kinetics: State of the art

“…Lignin pyrolysis chemistry is not that well understood in comparison to the other model components (cellulose and hemicellulose) due to its more complex structure. The bio‐oils from lignin consist of several aromatics, for example, benzene, toluene, biphenyl, and phenolics such as guaiacol, syringol, catechols, vanillins, and vinyl guaiacols (Bai et al, ; Custodis et al, ; Gai et al, ; Kawamoto & Saka, ; Khachatryan et al, ; Lou et al, ; Nowakowska et al, ; Scheer et al, ; Scheer et al, ). Lignin is known to decompose via competing pathways involving the bond cleavage of α‐O‐4, β‐O‐4, 5‐5 and 8‐5 bond linkages (Choi et al, ; Chu et al, ; Faravelli et al, ; Kawamoto & Saka, ; Kim et al, ).…”

“…In EPR analysis, the pyrolysis radicals undergo a transition via energy absorption, based on which the nature of detected radical can be analyzed. In these studies the samples are first pyrolyzed in simple micro-tubular reactors made up of quartz in an electrically heated furnace (Asatryan et al, 2017;Khachatryan et al, 2016;Khachatryan, Asatryan, McFerrin, Adounkpe, & Dellinger, 2010;Kim et al, 2014Kim et al, , 2015Xu et al, 2016). The reactor effluent is immediately quenched in quartz tubes immersed in a bath of liquid nitrogen to prevent the conversion of intermediate radicals.…”

“…Besides, these studies can also help in designing a suitable catalyst to improve the selectivity towards desired products (Butler et al, ; Li et al, ). Numerous studies have been performed over the years to decode the kinetic mechanisms of biomass fast pyrolysis (Agarwal, Dauenhauer, Huber, & Auerbach, ; Bai et al, ; Bai & Brown, ; Banyasz, Li, Lyons‐Hart, & Shafer, ; Bradbury, Sakai, & Shafizadeh, ; Branca, Di Blasi, Mango, & Hrablay, ; Broido & Nelson, ; Choi et al, ; Chu, Subrahmanyam, & Huber, ; Custodis, Hemberger, Ma, & van Bokhoven, ; Debiagi et al, ; Faravelli, Frassoldati, Migliavacca, & Ranzi, ; Gai et al, ; Huang, Liu, Tong, Li, & Wu, ; Huang, Liu, Wei, Huang, & Li, ; Kawamoto, Murayama, & Saka, ; Kawamoto & Saka, ; Khachatryan, Xu, Wu, Pechagin, & Asatryan, ; Kim, Bai, & Brown, ; Lou, Wu, & Lyu, ; Mayes & Broadbelt, ; Mayes, Nolte, Beckham, Shanks, & Broadbelt, ; Mettler, Mushrif, et al, 2012; Miller & Bellan, ; Norinaga, Shoji, Kudo, & Hayashi, ; Nowakowska, Herbinet, Dufour, & Glaude, ; Patwardhan, Dalluge, Shanks, & Brown, ; Patwardhan, Satrio, Brown, & Shanks, ; Piskorz, Majerski, Radlein, Vladars‐Usas, & Scott, ; Piskorz, Radlein, & Scott, ; Ranzi et al, , ; Ranzi, Debiagi, & Frassoldati, , ; Ronsse, Dalluge, Prins, & Brown, ; Scheer et al, ; Scheer, Mukarakate, Robichaud, Nimlos, & Ellison, ; Shafizadeh & Fu, ; Shen & Gu, ; Shen, Gu, & Bridgwater, ; Shen, Xiao, Gu, & Luo, ; Varhegyi, Jakab, & Antal, ; Vasiliou et al, ; Vinu & Broadbelt, ; Wang, Ru, Lin, & Luo, ; Werner, Pommer, & Broström, ; Zhang, Li, Yang, & Blasiak, ; Zhang, Nolte, & Shanks, ; Zhou, Li, Mabon, & Broadbelt, ; Zhou, Nolte, Mayes, Shanks, & Broadbelt,…”

“…Alternatively, model compounds of the three biomass constituents have been used to derive the details of intermediate species generated during their thermal decomposition. Pyrolysis of model compounds also provides insights on the influence of the substituent functional groups or bond linkages on the product distribution (Asatryan et al, ; Asmadi, Kawamoto, & Saka, ; Buckingham et al, ; Choi et al, ; Custodis et al, ; Jarvis et al, ; Kawamoto & Saka, ; Khachatryan et al, ; Lou et al, ; Nowakowska et al, ; Patwardhan et al, ; Robichaud, Nimlos, & Ellison, ; Scheer et al, ; Scheer et al, ; Scheer, Mukarakate, Robichaud, Ellison, & Nimlos, ; Vasiliou et al, ; Wang, McDonald, et al, ; Xu et al, ; Zhou, Nolte, et al, ).…”

“…These studies provide information on the dominant types of reactions involved such as concerted, free-radical, or ion-driven mechanisms. In addition, mechanistic studies describe the type of reaction intermediates and competing pathways involved in the product formation (Asatryan, Bennadji, Bozzelli, Ruckenstein, & Khachatryan, 2017;Bahrle, Custodis, Jeschke, van Bokhoven, & Vogel, 2014;Custodis et al, 2014;Furutani, Dohara, Kudo, Hayashi, & Norinaga, 2018;Khachatryan et al, 2016;Kibet, Khachatryan, & Dellinger, 2012;Kim, Bai, Cady, Gable, & Brown, 2015;Koirala, Villano, Carstensen, & Dean, 2013;Qi, Zhang, Kudo, Norinaga, & Hayashi, 2017;Seshadri & Westmoreland, 2012;Shen, Jarboe, et al, 2015;Wornat, Ledesma, & Marsh, 2001;Xu, Khachatryan, Baev, & Asatryan, 2016). Advances in analytical techniques have made it possible to even detect intermediate radicals and important product species (Bahng et al, 2009;Kanaujia, Sharma, Agrawal, & Garg, 2013;Michailof, Kalogiannis, Sfetsas, Patiaka, & Lappas, 2016;Negahdar et al, 2016;Pouwels, Eijkel, & Boon, 1989;Sarrut et al, 2015;Traore, Kaal, & Martinez Cortizas, 2016).…”