The Fundamentals of Biocarbon Formation at Elevated Pressure: From 1851 to the 21 st Century

Transcription

1 The Fundamentals of Biocarbon Formation at Elevated Pressure: From 1851 to the 21 st Century Michael J. Antal Jr, Charissa Higashi, Phacharakamol Phothisantikul, Sam Van Wesenbeeck, Simon Williams Hawaii Natural Energy Institute University of Hawaii at Manoa 21 May

2 Exponential Growth in PV Market Island of Maui In both 2011 and 2012, the installed PV on Maui doubled the total installed PV capacity of the prior year July, MW (Source: Maui Electric Company, Ltd.) Integrating High Penetrations of PV on Distribution Feeders Is a Challenge in Hawaii Today 2

3 C (Coal / Coke / Charcoal) Silicon Basic process Production (overview) SiO 2 (Quartz) SiO 2 (Microsilica ) CO 2 Surface 2SiO + O 2 = 2SiO 2 2CO + O 2 = 2CO 2 O 2 (air) Charge SiO(g) + 2C = SiC + CO 2SiO(g) = SiO 2 + Si SiC Inner reductionzone 3/ 12 SiO 2 + C + SiC = Si + SiO(g) + CO Silicon courtesy of Dr. Viktor Myrvagnes, Elkem SiO(g) SiO 2 + Si = 2SiO(g)

4 Metallurgical charcoal production in Brazil Courtesy of Dr. Scott Turn, HNEI 4

5 Thermochemical equilibrium predictions for the products of cellulose pyrolysis at 400 C 1 C, H 2 O, CO 2, (H 2,) and CH 4 are the only significant products. The theoretical charcoal (i.e. C) yield is 28 wt%. The gas contains significant energy (i.e. CH 4 ). Mass fraction (%) 50 CO 2 40 C(s) H 2 O(g) CH 10 4 (a) CO Pressure (MPa) 1) Antal et al., Ind. Eng. Chem. Res. 2003, 42,

6 Energy balance for cellulose pyrolysis following thermochemical equilibrium 1 cellulose specific heat carbon gas work exotherm sensible heat input output Energy [kj/kg-cellulose] 1) Antal et al., Ind. Eng. Chem. Res. 2003, 42,

7 Useful definitions: 1 1. y char = m char / m bio = % VM + % fc + % ash; where %VM = volatile matter; %fc = fixed carbon 3. y fc = y char {% fc / (100 - % feed ash)} 1) Antal et al., Ind. Eng. Chem. Res. 2000, 39,

8 Parity plot of fixed-carbon yields from various oak wood feedstocks 1 Flash Carbonization at elevated pressure attains y fc = 82% of the theoretical yield Muffle furnace yields in N2 at 1 bar are lower. TGA yields at 1 bar are much lower. Proximate analysis yields are very much lower. 1) Wang et al., Energy Fuels 2013, 27,

9 Themes of my presentation: 1. Is it possible to realize the theoretical y fc from biomass? 2. If it is possible, must the carbonization process be slow (and boring)? 3. Can such a carbonization process be practical (i.e. commercial)? 9

10 Effects of Avicel cellulose sample mass on char yield and TGA pyrolysis kinetics 1 Char yields at 400 C are VERY LOW Decreasing sample mass reduces char yield We hypothesize that in the limit of small sample mass, the char yield would be negligible. 1) Gronli et al., Ind. Eng. Chem. Res. 1999, 38,

11 Charcoal yield from cellulose pyrolysis vs. pressure 1 Pressure strongly favors formation of charcoal. Low gas flow rates also favor the formation of charcoal. Elevated pressure and low flow rates together double the yield of charcoal. 1) Mok and Antal, Thermochim. Acta. 1983, 68,

12 Violette, M. Memoire sur les Charbons de Bois. Ann. Chim. Phys. 1853, 32,

13 Highlights of Violette s 2 nd series of runs using sealed vessels: 1 1. DRY wood (1 g) carbonization from 150 to 350 C in sealed glass tubes (4 at each temperature with little void volume). 2. Each tube held in a metal safety container because carbonization created enormous gas pressures. 3. y char = 78.7% at 320 C in a sealed vessel with %C = 65.6% (vs. y char = 29.7% at 1 bar)! 4. Charcoal at 180 C resembles ordinary red charcoal at 280 C. 5. Charcoal at 300 C resembles coking coal having undergone melting: glossy, shiny, brittle and bonded to the glass tube. 6. Violette speculates that this is this how coal was formed. 7. Ash content of 3-4% vs. 0.5% with ordinary charcoal. 8. Also a milky opaque white, or (sometimes) clear yellow liquid product. 1) Violette, M. Memoire sur les Charbons de Bois. Ann. Chim. Phys. 1853, 32,

14 Who was Jules Henri Michel Violette?? Graduate of L Ecole Polytechnique Officer of the Legion D Honneur (1861) Commissaire of Powder & Saltpeter (n.b. Lavoisier was Regisseur of Powder & Saltpeter) Author of > 20 technical works (e.g. a dictionary of chemical analysis; experiments with the conservation of eggs; history of his company, etc.) Founder of a real estate company for the benefit of factory workers Thanks to Mme. Larence Chevrier, Bibliotheque Nationale de France 14

15 DSC traces of heat release from cellulose & xylan in closed crucibles 1 At high loadings charcoal formation from cellulose is complete below 300 C. The reaction rate is greatly enhanced in a closed crucible Xylan is converted to charcoal below 240 C. Pyrolysis is exothermic for all cases. 1) Mok et al., Ind. Eng. Chem. Res. 1992, 31,

16 Effects of moisture on heat release & char yield from cellulose in closed crucibles 1 At high moisture content charcoal formation is complete below 300 C. The reaction rate is greatly enhanced by high moisture content The char yield is greatly enhanced by high moisture content Pyrolysis is exothermic for all cases. 1) Mok et al., Ind. Eng. Chem. Res. 1992, 31,

17 A kinetic model for the observed DSC traces that employs water catalysis 1 Cellulose pyrolysis in sealed sample holders: H 2 O H 2 O cellulose intermediates char + H 2 O + gases k 1 k 2 k 0 char + volatiles + H 2 O + gases Reaction 0 is the non-catalyzed decomposition observed in open pan TG experiments. Reaction 1 is the hydrolysis of cellulose in the presence of water. Reaction 2 is the secondary reaction of the intermediates in the sealed sample holder. The rates of reactions 1 and 2 depend on the amount of water vapors in the system. 1) Varhegyi et al., J. Anal. Appl. Pyrolysis 1997, 42,

18 Fit of the kinetic model to the DSC data for cellulose carbonization in a sealed crucible Rate of heat release (mw/mg) C Differential scanning calorimetric study of cellulose carbonization in hermetically sealed sample holders at 5 C/min heating rate. The symbols (,,...) represent experiments differing in the initial sample mass and 1) Varhegyi et al., J. Anal. Appl. Pyrolysis 1997, 42,

19 What does a tubing bomb look like? 19

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21 Summary of tubing bomb results 21

22 A liquid melt phase precedes the formation of biocarbon with high y fc ; linking high pressure phenomena to high heating rate phenomena! 22

23 Conclusions With >32,000 years of experience, we now understand the conditions needed to realize the theoretical fixed-carbon yield of charcoal from ash-free cellulose. These conditions involve fast pyrolysis in a sealed vessel that reaches pressures exceeding 200 psig. In 1853 Violette reported amazingly prescient research concerning charcoal production in sealed vessels (but he did not measure the fixed-carbon yield). The observation of a liquid phase in charcoal formation links high pressure pyrolysis chemistry to high heating rate pyrolysis chemistry. 23

24 Conclusions (continued) Numerical simulations of sealed vessel results (e.g. pressure, temperature gradients, gas and char fc and VM compositions) will reveal much about the mechanism of cellulose pyrolysis. It may be possible to build commercial equipment that employs sealed vessels to realize the theoretical fixedcarbon yield of charcoal in a practical situation. Advice to young researchers: A year of long days, late evenings and weekends in the laboratory will save you an afternoon of reading interesting papers in the library. 24

25 Acknowledgments Dr. Maria Burka & Ms. Bonnie Thompson (National Science Foundation) Office of Naval Research Prof. Colomba DiBlasi (Università degli Studi di Napoli "Federico II) Jan Piskorz (Resource Transforms Int. Ltd.) Dr. Gabor Varhegyi, Dr. Piroska Szabo, Dr. Emma Jakab, Dr. Marianne Blazso (Hungarian Academy of Sciences) Dr. Morten Gronli, Dr. Oyvind Skreiberg, Dr. Liang Wang (NTNU & SINTEF) 25

26 Three co-authors (Szabo, Varhegyi, and Antal ca. 1990) of the 1992 DSC paper with Emma Jakab,and Linda in the HAS Budapest laboratory

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28 21 May 2014 Supplementary slides follow this slide

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30 DSC traces of charcoal formation from woods in closed crucibles 1 Charcoal formation is complete below 350 C for all species. Hemicellulose is converted to charcoal below 300 C. Pyrolysis is exothermic for all species. 1) Mok et al., Ind. Eng. Chem. Res. 1992, 31,

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