Stability of fast pyrolysis bio-oils and upgraded products TCBiomass13 Anja Oasmaa, VTT, Finland Douglas C. Elliott, PNNL, USA VTT Technical Research Centre of Finland
2 Content Composition of fast pyrolysis bio-oils Stability phenomena Stability measurement Stability improvement Conclusions
Yield wt% based on dry feed 11/09/2013 3 Definitions 100 80 60 wt% 40 20 0 WATER PINE Singlephase liquid Energy & Fuels, 2010, 24, pp. 1380-1388 CHAR GAS WATER WATER BIO-OIL Feedstock moisture Pyrolysis CHAR water GAS Fast pyrolysis of biomass Rapid (1-2 s) thermal (abt. 500 WATER PYRWAT ORG Liquid organic product Ageing C) degradation of biomass under inert atmosphere into biooil as main product and into sideproducts gases, and char chemical process where during storage the reactive organic components in bio-oil react to form larger molecules (polymerize) and consequently cause changes in physical properties, such as an increase in viscosity.
4 Chemical composition of fast pyrolysis bio-oils High amount of reactive oxygen functionality and acidic environment causes changes in bio-oil during storage Energy & Fuels, 2003, vol. 17, 2, pp. 433 443 Energy & Fuels, 2008, vol. 22, 6, pp. 4245 4248
5 Increase in molecular weight during ageing Diebold, J. 2002. A Review of the Chemical and Physical Mechanisms of the Storage Stability of Fast Pyrolysis Bio-Oils. http://www.nrel.gov/docs/fy00osti/27613.pdf Polymerization processes play an important role in the aging behavior of bio-oils
6 Effect of time and temperature on viscosity increase Diebold, J. 2002. A Review of the Chemical and Physical Mechanisms of the Storage Stability of Fast Pyrolysis Bio-Oils. http://www.nrel.gov/docs/fy00osti/27613.pdf The instability of bio-oils can be observed as increased viscosity over time, particularly when heated
Amount, wt % of d.m. 11/09/2013 7 Effect of time and temperature on chemical composition 50 45 40 35 30 25 20 15 10 5 Sugars Water insolubles Aldehydes, ketones, etc. 0 0 1 2 3 4 5 6 7 8 9 10 11 12 Storage time, months No changes in cold 100 90 80 70 60 50 40 30 20 10 0 Data has been produced by following changes of several softwood and hardwood pyrolysis liquid at room temperature. Ref. Oasmaa, Anja. 2003. Fuel oil quality properties of wood-based pyrolysis liquids. Academic dissertation. Jyväskylä. Department of Chemistry, University of Jyväskylä. 32 p. + app. 251 p.. Research Report Series, Report 99. Doctoral thesis Stability test Volatile acids Aldehydes, ketones Ether-insolubles Ageing can be seen in chemical composition as increase in WIS By decreasing temperature no changes in chemical composition happens Ageing at 80 C for 24 hours causes roughly same chemical changes and viscosity increase than 1 year storage at room temperature Water LMM lignin + extractives + pol.product HMM lignin + pol.products
8 Stability indicators The viscosity increase-based stability test (80 C for 24 h) measures the change in viscosity of the pyrolysis liquid Increase in Mw by GPC correlates with increase in viscosity and in WIS (water-insolubles) The change in carbonyl content (by titration, FTIR, NMR,...) of bio-oil correlates with the change in viscosity measured by the stability test Energy & Fuels. vol. 25, 7, ss. 3307-3313 Scholze, B. Dissertation 2002. Diebold, J. 2002. http://www.nrel.gov/docs/fy00osti/27613.pdf Fratini et al. Langmuir 2006, 22, 306-312 Oasmaa, Anja; Peacocke, Cordner. 2010. VTT Publications; 731 Elliott, D. C.; Oasmaa, A.; Preto, F.; Meier, D.; Bridgwater, A. Energy Fuels 2012, 26, 3769 3776.
9 Round robins on stability method Several round robins on stability have been carried out: The difference in the implementation of the method among the participating laboratories makes the reproducibility of the accelerated aging test quite low and not the method itself. Heat transfer is the key point for improving stability test. It may be more useful to prescribe the use of a heating bath rather than an oven, to have better temperature control. At VTT use of water bath has been successively tested and modified method will be available in http://www.pyne.co.uk/ Elliott, D. C.; Oasmaa, A.; Preto, F.; Meier, D.; Bridgwater, A. V. Results of the IEA round robin on viscosity and stability of fast pyrolysis bio-oils. Energy Fuels 2012, 26, 3769 3776. Oasmaa, A.; Meier, D. Pyrolysis liquids analyses: The results of IEA EU round robin. Fast Pyrolysis of Biomass: A Handbook; Bridgwater, A. V., Ed.; CPL Press: Newbury, U.K., 2002; Vol. 2, pp 41 58 Oasmaa, A.; Meier, D. Norms and standards for fast pyrolysis liquids 1. Round robin test. J. Anal. Appl. Pyrolysis 2005, 73 (2), 323 334. McKinley, J. W.; Overend, R. P.; Elliott, D. C. The ultimate analysis of biomass liquefaction products: The results of the IEA round robin #1. Proceedings of the Specialist Workshop on Biomass Pyrolysis Oil Properties and Combustion; Estes Park, CO, Sept 26 28, 1994; CP-430-7215, pp 34 53.
10 Stability improvement by solvents Pyrolysis Oil (PO) PO + 5% alcohol PO + 10% alcohol Dilution, solubilisation - Alcohol (and water up to 30 wt%) addition improves the solubility and dilutes the bio-oil and retards the aging reactions Esterification, acetalization - Stability improvement by elimination of acid catalysts, and acetalization of reactive carbonyl groups. Additional effect on stability caused by solvent. Increasing amount of solvent decreases the viscosity increase during aging by improving solubility and preventing the association reactions
11 Stability improvement by catalytic upgrading HDO - By hydrotreating oxygen is removed in the form of water and reactive functionalities stabilized Catalytic pyrolysis - By catalytic pyrolysis highly reactive oxygenate functionalities are removed in the form of water and carbon oxides and mainly more stable aromatic structures form the main constituents
12 HDO of fast pyrolysis bio-oils - - Zacher et al. tcbiomass 2013; Olarte, MV, et al. 2013. pre-print submitted to ENFL, 246th ACS National Meeting - PNNL demonstrated recently long-term HDO (over 1400 h) in a two-stage 400-ml fixed bed continuous reactor Low-temperature hydrotreatment reduced carbonyl groups associated with polymerization reactions, enabling longer term upgrading of pyrolysis oil Stabilization was seen also as a clearer smaller viscosity increase
13 Catalytic pyrolysis Organics decrease Aromaticity increases Distillability improves Acids decrease Methoxyl functionalities decrease Carbohydrates decrease Carbonyls decrease V Paasikallio et. al 2013 Results from other research groups, i.a. USU, NREL, UMass, USDA, ISU, CPERI, U of Twente, included Stability of catalytic pyrolysis products improves by decreasing reactive oxygen functionality but is much more complex issue than with fast pyrolysis bio-oils
14 Accuracy of analytical methods Property Methods Standard Validated Comments Compounds for bio-oils on accuracy Water ASTME203 IEA RR Good if proper calibration is carried out Acidity TAN ASTMD664 VTT-PNNL RR needed ASTMD3339 RR needed ph IEA RR Not accurate Acid composition by CE or GC/MSD VTT-RUG-Thunen Accurate but prone to errors Carboxylic acids by 13C-NMR CHN ASTMD5291 IEA RR Typically good, but prone to errors Ash Ashing in oven EN7 Needs large sample size to be accurate MCR MCR + ashing Reasonable good Oxygen From CHN, ash as difference IEA RR Errors in CHN are seen in O Viscosity Kinematic ASTMD445 IEA RR Good Dynamic IEA RR Typically good, but prone to errors Stability Viscosity increase 24h 80C IEA RR Not validated for upgraded oils Carbonyls Carbonyl content by titration Reasonable good Aldehydes, ketones by solvent fractionation Good but needs practizing Ketone and aldehyde carbonyls by 13C-NMR Carbohydrates 13C-NMR Brix by density meter Reasonable good Solvent extraction Good but needs practizing Lignin Water-insolubles Standard method needed Pyrolytic lignin Standard method needed Aromatics, olefins, phenolics 13C-NMR Aliphatic hydrocarbons 13C-NMR Distillability Simulated distillation by GC ASTM D 2884 No Non-GC-eluted fraction is not included Atmospheric/vacuum distillation No Good Suitability for oil refinery Micro Activity Tester ASTM D-3907 No Several modifications Analytical methods used for stability should be validated by round robins
15 Conclusions Stability of fast pyrolysis bio-oils and upgraded products is improved by Decreasing the amount of highly reactive species, especially carbonyl compounds, methoxyl functionality, and furfurals Decreasing the amount of catalysts, like acids and alkali metals Increasing the relative amount of solubilisation agents like alcohols Analytical methods should be validated and standardised Stability is a complex phenomena, especially as numerous various catalysts are involved. Hence, the required stability should be specified case by case depending on use of the bio-oil.
16 Thank you! Acknowledgments to Eeva Kuoppala, Ville Paasikallio, Yrjö Solantausta, Tom Sundqvist Feedback and nasty questions: anja.oasmaa@vtt.fi