(600a) Effect of Carbonaceous Susceptors on Selective Production of Phenolics and Syngas from Lignin Via Microwave Pyrolysis
AIChE Annual Meeting
2017
2017 Annual Meeting
Topical Conference: Innovations of Green Process Engineering for Sustainable Energy and Environment
Efficient Processing of Lignin to Bioproducts and Biofuels II
Wednesday, November 1, 2017 - 3:15pm to 3:37pm
The intention of the current study is to enhance the yield of bio-oil and its quality from lignin by microwave assisted pyrolysis. The effects of (i) lignin (L) to activated carbon (AC) ratio , (ii) particle size of activated carbon (0.45 mm to 3 mm), and (iii) carbonaceous susceptors (AC, graphite and charcoal) on heating rate, product yields (oil, gas and char fractions), product composition and process efficiency were investigated at a constant microwave power of 480 W. It was found that, owing to the high amount of physically bound moisture in the mesoporous capillaries of AC (1mm), high bio-oil yield of 66 wt. % at optimum conditions of 10: 90 g/g of L: AC was observed. In L:AC blend of 100 g, increase in mass of AC from 10 g to 90 g decreased the heating rate significantly from 128 oC/min to 32 oC/min, correspondingly a decrease in energy efficacy of the system from 95% to 34% was observed. From the oil composition analyses, it was found that bio-oil comprises of phenolics (simple phenols, guaiacols and syringols), aromatic hydrocarbons, naphthalenes, indene derivatives and furans. The highest yield of total phenolics (64.2%) was obtained at 10: 90 g/g of L: AC (1mm). Initial lignin sample mass of 9 to 40 wt. % was converted into simple phenolics and its composition increased with increase in L: AC ratio.
The carbonaceous materials, such as activated carbon, graphite, charcoal and bio-char are found to be the efficient microwave absorbers because of their high microwave coupling nature even at ambient temperatures [1,2]. For this reason, we have chosen activated carbon, graphite and charcoal as the susceptors to investigate their effect on lignin pyrolysis. The effect of susceptors on the heating rate, product mass and energy yields were investigated. The yield (wt. %) of bio-oil is in line with the heating rates and varies in the following order: charcoal (36 wt. %) > graphite (34.5 wt. %) > AC (0.45mm) (29.2 wt. %). Phenolic derivatives are dominant in oil fraction, 97% of oil obtained with AC (0.45mm) contains phenolics followed by charcoal (79%) and graphite (72%). Selectivity (%) of simple phenolics is varying in the following order: 60.1 (AC (0.45mm)) > 55.8 (charcoal) > 40.9 (graphite). A significant enhancement in heating value was noticed both in char (28-30 MJ/kg) and oil (28-33 MJ/kg) fractions compared to raw lignin (25 MJ/kg). Tiny micro plasma spots generated during the pyrolysis process increased tiny cylindrical and spherical micro-pores within the residual char. Yield of CO2 decreased and that of H2 increased with increase in pyrolysis temperature and its evolution profiles were influenced by the nature of susceptor and lignin to susceptor mass ratio.
References:
- T. Ohra-aho, J. Linnekoski. Catalytic pyrolysis of lignin using analytical pyrolysis-GC-MS. J. Anal. Appl. Pyrol. 113 (2015) 186-92.
- S. Adhikari, V. Srinivasan, O. Fasina. Catalytic pyrolysis of raw and thermally treated lignin using different acidic zeolites. Energy & Fuels 28 (2014) 4532-38.