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Title: Effect of torrefaction temperature on lignin macromolecule and product distribution from HZSM-5 catalytic pyrolysis

Torrefaction is a low-temperature process considered as an effective pretreatment technique to improve the grindability of biomass as well as enhance the production of aromatic hydrocarbons from Catalytic Fast Pyrolysis (CFP). For this paper, this study was performed to understand the effect of torrefaction temperature on structural changes in the lignin macromolecule and its subsequent influence on in-situ CFP process. Lignin extracted from southern pine and switchgrass (via organosolv treatment) was torrefied at four different temperatures (150, 175, 200 and 225 °C) in a tubular reactor. Between the two biomass types studied, lignin from pine appeared to have greater thermal stability during torrefaction when compared with switchgrass lignin. The structural changes in lignin as a result of torrefaction were followed by using FTIR spectroscopy, solid state CP/MAS 13C NMR, 31P NMR spectroscopy and it was found that higher torrefaction temperature (200 and 225 °C) caused polycondensation and de-methoxylation of the aromatic units of lignin. Gel permeation chromatography analysis revealed that polycondensation during torrefaction resulted in an increase in the molecular weight and polydispersity of lignin. The torrefied lignin was subsequently used in CFP experiments using H +ZSM-5 catalyst in a micro-reactor (Py-GC/MS) to understand the effect of torrefaction on themore » product distribution from pyrolysis. It was observed that although the selectivity of benzene-toluene-xylene compounds from CFP of pine improved from 58.3% (torrefaction temp at 150 °C) to 69.0% (torrefaction temp at 225 °C), the severity of torrefaction resulted in a loss of overall aromatic hydrocarbon yield from 11.6% to 4.9% under same conditions. Torrefaction at higher temperatures also increased the yield of carbonaceous residues from 63.9% to 72.8%. Finally, overall, torrefying lignin caused structural transformations in both type of lignins (switchgrass and pine), which is ultimately detrimental to achieving a higher aromatic hydrocarbon yield from CFP.« less
 [1] ;  [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [3] ;  [4]
  1. Auburn Univ., AL (United States). Dept. of Biosystems Engineering
  2. RTI International, Durham, NC (United States). Energy Technology Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biosciences Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemical and Biomolecular Engineering
Publication Date:
Grant/Contract Number:
AC05-00OR22725; USDA-NIFA-2015-67021-22842; NSF-CBET-1333372
Accepted Manuscript
Journal Name:
Journal of Analytical and Applied Pyrolysis
Additional Journal Information:
Journal Volume: 122; Journal ID: ISSN 0165-2370
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Auburn Univ., AL (United States); RTI International, Durham, NC (United States)
Sponsoring Org:
USDOE; USDA; National Science Foundation (NSF)
Contributing Orgs:
Univ. of Tennessee, Knoxville, TN (United States)
Country of Publication:
United States
09 BIOMASS FUELS; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Biomass; Catalytic fast pyrolysis (CFP); HZSM-5; Torrefaction; Lignin
OSTI Identifier: