Characterization of pyrolyzed lignin chars for use in a novel foundry fuel source

Open Access
Author:
Frantz, Curtis Wendelin
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
February 25, 2013
Committee Members:
  • Nicole Robitaille Brown, Thesis Advisor
Keywords:
  • lignin
  • pyrolysis
  • NMR
  • char
Abstract:
Briquettes containing 86-92% anthracite fines, 2.3-8.6% lignin, 4.5% silicon metal powder, and 0.9% hydrolyzed collagen (gelatin) by mass have been investigated as a promising coke replacement in the foundry industry. The inclusion of lignin is important; we hypothesize it thermally fuses, providing the necessary strength for the briquettes to maintain their structural integrity throughout the extremely harsh pyrolitic conditions of the foundry’s cupola furnace. In order to mimic the cupola environment, eucalyptus hardwood lignin has been pyrolyzed at a series of temperatures ranging from 300°C to 800°C for either 5, 10, or 20 minutes. Following pyrolysis the lignin samples were subjected to nuclear magnetic resonance spectroscopy (NMR), pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy to gain insight into either the reaction mechanism or the structure of the resultant lignin char. The results of these techniques indicate that the content of aromatic carbon within the lignin increases from 54.1% to 95.6% between the control (un-pyrolyzed) lignin and the lignin pyrolyzed at 500°C for 20 minutes. The average distance between aromatic carbons and their nearest hydrogen atom also increased, indicating the size of aromatic domains is increasing. The XRD data indicate that while the lignin has not become ordered and aromatic enough to be considered “graphitic”, the order and crystallinity is increasing and was trending in the direction of graphite. The diffraction pattern of the 800°C sample roughly resembled the patterns of soots and glassy carbon. Similarly, the Raman spectra of samples pyrolyzed from 400°C to 800°C indicate that the lignin was becoming more ordered; the disordered (D) and graphitic (G) peaks became more defined within samples pyrolyzed at high temperature. The samples did not reach a high level of graphitization but contained ordered aromatic regimes.