Lignin Depolymerization and Conversion Utilizing Catalytic Hydrogenolysis

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Lignin Depolymerization and Conversion Utilizing Catalytic Hydrogenolysis

  1. 1. LIGNIN DEPOLYMERIZATION THROUGHHYDROGENOLYSIS INTO MONOMERIC SUBUNITS ON METAL CATALYSTS Lis Nimani Advisor: Dr. Xuejun Pan Master of Science Thesis Defense August 3rd, 2012
  2. 2. Outline Introduction  Renewable energy  Lignocellulosic Biomass  Polysaccharides  Lignin  Conversion Processes of Lignocelluloses to Fuels and Chemicals  Lignocellulose conversion  Problem Statement  Objectives Hydrogenolysis  Hydrogenolysis Operation  Hydrogenolysis of Feedstock  Lignin Hydrogenolysis  Polysaccharides Hydrogenolysis Conclusion  Summary  Future Work
  3. 3. Renewable Energy Need for renewable energy  Depletion of Fossil Fuels  Global Warming due to Greenhouse Gasses (GHGs)  National Security (Deming, 2000) (Forster et al., 2007) (Akorede et al., 2012) Bioenergy  Corn/Sugarcane (1st Generation)  Lignocellulosic Biomass (2nd Generation)
  4. 4. Lignocellulosic Biomass  Lignocellulosic Biomass  Hardwood  Softwood  Herbaceous Plants  Lignocellulose Complex (Murphy and McCarthy, 2005)  Cellulose  Hemicellulose  Lignin The chemical composition make up of the lignocellulosic materials (Sun and Cheng, 2002)Feedstock Cellulose (%) Hemicellulose (%) Lignin (%)Hardwood 40-50 25-40 18-25Softwood 45-50 25-35 23-35 (Zhou et al., 2010) Grasses 25-40 35-50 10-30
  5. 5. Polysaccharides Cellulose  Most abundant organic chemical on earth.  Homopolymer  7,000 to 15,000 monomeric D- glucose units  Crystalline and Amorphous Regions (Meyers et al., 2008)  Up to 65% crystalline regions in Content and compositional differences between hardwood vs. softwood wood. (Kögel-Knabner, 2002) Hemicellulose Polyoses Deciduous Wood (Hardwood) Coniferous Wood (Softwood) Content (%) Units Content (%) Units  Branched Heteropolymers Xylose, 4-O- Xylose, 4-O-  Pentoses (β-D-xylose, α-L- Xylans 25-30 methylglucuronic 5-10 methylglucuronic acid acid arabinose) Mannose, glucose,  Hexoses (β-D-mannose, β-D- Mannans 3-5 Mannose, glucose 20-25 galactose, acetyl groups glucose, α-D-galactose) Galactose, Galactose, Galactans 0.5-2 arabinose, 0.5-3  Xylans and Glucomannans rhammose arabinose  Most significant hemicelluloses.
  6. 6. Lignin An amorphous three-dimensional bio-polymer of three phenylpropane units randomly cross-linked with one another.  Derived generally from three monolignols:  Para-coumaryl alcohol  Coniferyl alcohol  Sinapyl alcohol  Monolignols produce phenylpropaniod units  Para-hydroxyphenol (H-unit) (Xu, 2010)  Guaiacyl (G-unit)  Syringol (S-unit) Lignin is produced by free radical generation followed by chemical coupling processes of the monolignols.
  7. 7. Lignin Lignin content and composition varies between lignocellulosic biomass.  Lignin content  Softwoods ˃Hardwoods ˃ Herbaceous  Lignin composition  Softwood: Guaiacyl (G) lignin  Hardwood: Guaiacyl-syringol (GS) lignin  Herbaceous: Gramineae (GSH) lignin  Lignin linkages  (1/3) to (1/4) carbon-carbon linkages  (2/3) to (3/4) ether linkages
  8. 8. Lignin (Kögel-Knabner, 2002) Content of the main linkages in lignin (Faravelli et al., 2010) (Achyuthan et al., 2010; Pandey and Kim, 2011; Ralph, 2005; Zakzeski et al., 2010) Linkage Type Softwood (spruce) (%) Hardwood (birch) (%) β-O-4-Aryl ether 46 60 Dibenzodioxocin 25-30 5-10 β-5-Phenylcoumaran 9-12 6 β-β-(Resinol) 2-6 3-12 4-O-5-Diaryl ether <4 <6.5β-1-(1,2-Diarylpropnae) 1-2 1-2 α-O-4-Aryl ether A few A few
  9. 9. Conversion Processes of Lignocelluloses to fuels and Chemicals (Menon and Rao, 2012) Comparison between the biochemical and thermochemical process (Basu 2010a). Biochemical Process Thermochemical Process Reactor Type Batch Continuous Reaction Time A few Days A few minutes Temperature 100-200 °C ˃ °C 200 Water Usage (liter/liter ethanol) 3.5-170 <1
  10. 10. Lignocellulose Conversion (Zheng et al., 2011)
  11. 11. Problem Statement Current biochemical conversion of lignocellulose for fuels and chemicals  Cellulose and hemicellulose converted to ethanol  Lignin used as a boiler fuel through combustion  Non-simultaneous Inefficient utilization of lignin  2nd most abundant polymer  15-30% of biomass  Higher energy content than cellulose Celunol Corp. http://zfacts.com/p/85.html. 27, July 2012.  9,000-11,000 Btu/lb vs. 7,300- 7,500 Btu/lb  Production of phenols and phenol
  12. 12. Objectives Thermochemical conversion of feedstock for fuel and chemical precursors  Polysaccharides followed by lignin conversion  Ethanol and lignin derived chemicals  Simultaneous conversion of feedstock  Polysaccharides and lignin derived chemicals Hydrogenolysis of feedstock using noble-metal catalysts  Lignin Hydrogenolysis  Main focus  Depolymerization of lignin into fuel and chemical precursors  Factors affecting lignin hydrogenolysis  Lignin monomer yield  Polysaccharides hydrogenolysis  Conversion of polysaccharides into fuel and chemical precursors  Factors affecting polysaccharide hydrogenolysis
  13. 13. Hydrogenolysis Operation Reference experiment run: Residence time: 4 hours Temperature: 200 ºC Pressure: 1000 psi Catalyst: Pt/C Mineral acid: Phosphoric Acid Solvent: Water/dioxane (1:1, v/v)Hydrogenolysis Operation Parr Reactor
  14. 14. Hydrogenolysis of Feedstock Conversion of feedstock:  Based on the weight of feedstock utilized in the reaction and the solid recovered after reaction  Amount dissolved  Liquid soluble product  Converted feedstock (%)  Liquid insoluble product  Solid residue Higher feedstock conversion More fuel and chemical precursors possible  Due to less solid residueFeedstock Conversion 100 80 Conversion (%) 60 40 20 0 in r e ce se in la av n n ru lo p ig lig g o lu p A L P S el lv i al C so lk o A an rg O Feedstock Conversion of different feedstocks through catalytic hydrogenolysis. The reaction conditions were: Residence time: 4 hours; temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v).
  15. 15. Hydrogenolysis of Feedstock Poplar conversion (amount dissolved) for Poplar Conversion different reaction 100 conditions 80 Conversion (%) Higher conversion 60  Higher temperatures 40  Presence of mineral acid  Water solvent 20 15 10 5 Lower conversion 0 71 a 80 92 39 82 84 72 73 40 47 86 88 90 98 65 67 69 5 9 4 0 2 10 10 10 10 10  Lower temperature Experimental control run a Run #  Absence of mineral acid Poplar feedstock conversion when an operational variable is changed during catalytic hydrogenolysis. The reaction conditions were: Residence time: 4 hours; temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; (phosphoric acid) phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v), while one of the conditions was changed and the rest kept as  Ethanol solvent listed. No effect on conversion  Catalyst and catalyst
  16. 16. Lignin Hydrogenolysis Lignin depolymerization into fuels and chemical precursors  Selective cleavage of ether bonds  Lower temperature  No carbon-carbon linkage cleavage  Higher temperature (Faravelli et al., 2010) Isolated lignin i.e. organosolv lignin and alkali lignin  Lignin structure already altered due to isolation
  17. 17. Lignin Hydrogenolysis Selective production of monomers and/or dimers  Monomers  Monomer units in the native lignin linked to other monomer units by ether bonds depolymerized into monomers  Dimers  A lignin monomer linked to another monomer unit through a carbon-carbon linkage, while at the (Yan et al., 2008)
  18. 18. Lignin Hydrogenolysis Hydrogen molecules react with catalyst  Hydrogen molecule sigma bond broken  Weaker metal-hydride bond formed The sigma bond in the C-O bond interacts with the metal catalyst  Weakens metal hydride bond  Hydrogen atom is transferred to oxygen(C-O bond) Second hydrogen atom is transferred from the catalyst to carbon  Weakened sigma bond gets (Nagy et al., 2009) cleaved
  19. 19. Lignin Hydrogenolysis Ideal monomer theoretical yield  Probability of a monomer linked to two other monomer through ether linkages is the square of the ether linkages in lignin.  Ether linkages  (2/3) to (3/4) of lignin linkages  Simplified model  More ether linkages in hardwood than softwood  Guaiacyl lignin contains less ether linkages  Resulting in 44-56% theoretical yield for monomers. (Yan et al., 2008)  Assumptions  All ether linkages cleaved Not possible for isolated lignin  Do not know ether content in isolated lignin
  20. 20. Lignin Hydrogenolysis Reference condition GC/MS  Monomers  Guaiacylpropane  Syringylpropane  Dimers  Not detected Reaction conditions  Peaks with different retention times  Not identified Gas Chromatography and mass spectrum analysis. The reaction conditions were: Residence  Guaiacylpropane and time: 4 hours; temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar. Syringylpropane still predominate. Previous Studies  Guaiacylpropanol and syringylpropanol in addition to
  21. 21. Lignin Hydrogenolysis Factors affecting lignin hydrogenolysis  The effect of residence time  The effect of temperature  The effect of hydrogen pressure  The effect of feedstock  The effect of noble-metal catalyst  The effect of addition of mineral acid  The effect of solvent Compared by lignin yield (%,w/w)  Based on initial lignin in feedstock  Guaiacylpropane and syringylpropane end-product
  22. 22. Lignin Hydrogenolysis The effect of residence Residence Time Effect time on lignin 60 hydrogenolysis 2 hrs  Time needed to reach maximum 4 hrs Yield (%,w/w) temperature included. 6 hrs 40 Linear relationship between 8 hrs residence time and lignin yield 20  Linear regression analysis 0 statistically significant s s s s hr hr hr hr  Residence time does a 2 4 6 8 somewhat decent job of Residence Time (hours) predicting lignin monomer yield Lignin product yield during catalytic hydrogenolysis while varying the residence times. The  R2 = 0.73 reaction conditions were: temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar. The residence time
  23. 23. Lignin HydrogenolysisThe effect of temperature Temperature Effect on lignin 50 hydrogenolysis 150 (°C) 40 200 (°C) Significant linear Yield (%,w/w) 250 (°C) relationship between 30 300 (°C) temperature and lignin yield 20 for (150 to 250 ºC) 10  Linear regression analysis not 0 ) ) ) statistically significant between ) (°C (°C (°C (°C 0 0 0 150 to 300 ºC 0 15 20 25 30  Temperature is not a good Temperature predictor of lignin monomer Lignin product yield during catalytic hydrogenolysis while varying the temperature. The reaction yield conditions were: Residence time: 4 hours; Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar.  R2 = 0.61 The temperature treatments
  24. 24. Lignin Hydrogenolysis The effect of Pressure Effect hydrogen pressure 60on lignin hydrogenolysis 0 psi 250 psi Yield (%,w/w) 40 1000 psi A minimal pressure between 0 and 250 psi is 20 necessary for initiation of hydrogenolysis 0 No linear relationship i i i ps ps ps 0 0 00 25 between pressure and 10 Pressure (psi) lignin yield between 250 psiproduct yield during catalytic hydrogenolysis while varying the hydrogen pressure. The Lignin and 1000 psi reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; catalyst: 10% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar. The pressure treatments were statistically different.
  25. 25. Lignin Hydrogenolysis Feedstock EffectThe effect of feedstock 60 Agave Poplar on lignin Yield (%,w/w) 40 Spruce Organosolv Lignin hydrogenolysis 20 Alkali Lignin The feedstock treatments were statistically different. 0 in e r e in la v uc gn gn  Poplar generated the highest ga op pr Li Li A P S i lv al so lk yield A o an rg O Woods Feedstock  Poplar yield > Spruce yield S/Ga (%) versus Feedstock  S/G ratio 5 Agave 4 Poplar  Spruce contains Guaiacyl Yield (%,w/w) Spruce 3 lignin Organosolv lignin Alkali Lignin 2 Agave 1  S/G ratio ~ 2:1 0 in in e r ce la av  Para-hydroxyphenol unit n n ru p lig ig g o p A L P S lv i al so lk o A an Isolated lignin O rg Feedstock  Organosolv lignin a S/G: syrignylpropane to guaiacylpropane  Small monomer yield Lignin product yield and monomer selectivity during catalytic hydrogenolysis while varying the feedstock. The reaction conditions were: Residence time: 4 hours; Temperature: 200 °C;  S/G ratio ~ 4:1 Pressure: 1000 psi; catalyst: 10% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H 2O (1:1,v/v).  Alkali lignin
  26. 26. Lignin Hydrogenolysis The effect of noble-metal Catalyst Effect on Poplar catalyst on lignin 100 Pt/C 80 Pt/G hydrogenolysis Yield (%,w/w) Pd/C 60 Rh/CaPoplar 40 Noneb Catalyst is necessary 20 0  Lowers the activation energy of Ca b C t/G t/C e d/ on h/ P P P R N reaction Catalyst Type a Values greater than theoretical 44%  Allows for homolytic dissociation of b Same reaction conditions S/Ga (%) versus Catalyst H2 molecules 5 Pt/C The catalyst treatments were not 4 Pt/G Yield (%,w/w) Pd/C statistically different for lignin yield. 3 Rh/C  Rh/C was not included because 2 produced values greater than theoretical 1 yield 0  Outlier /C C /G /C h/ Pd Pt Pt R Catalyst treatments were a Catalyst Type S/G: syrignylpropane to guaiacylpropane statistically significant for S/G ratio. Lignin product yield and monomer selectivity during catalytic hydrogenolysis while varying the  Pd/C higher S/G ratio catalyst on poplar. The reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w); phosphoric acid: 40% (w/w); solvent: H 2O (1:1,v/v);  Higher selectivity for syringylpropane feedstock: poplar.
  27. 27. Lignin Hydrogenolysis The effect of noble-metal catalyst Catalyst Effect on Organosolv Lignin 15on lignin hydrogenolysis Pt/C Pt/GOrganosolv lignin Yield (%,w/w) 10 Pd/C The catalyst treatments Rh/C were statistically different for 5 lignin yield.  Rh/C produced the highest yield followed by Pt/G 0 /C /C /G /C Pd Rh Pt Pt  Tukey’s Multiple comparison Catalyst Type Lignin product yield during catalytic hydrogenolysis while varying the catalyst on organosolv test lignin. The reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; Pressure:  Rh/C statistically different to Pt/C and Pd/C 1000 psi; catalyst: 10% (w/w); phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock:  Pt/G and Rh/C not statistically poplar. different.
  28. 28. Lignin Hydrogenolysis The effect of noble-metal catalyst on lignin hydrogenolysis Catalyst loadingPoplar Linear relationship between catalyst loading and lignin yield Linear regression of catalalysts loading versus yield of lignin monomers for poplar. The reaction conditions were: Residence time: 4 hours; temperature: 200 °C; pressure: 1000 psi; catalyst:  Linear regression analysis statistically 10% and 40% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar. significant  Catalyst loading can predict lignin monomer yield to a certain accuracy.  R2 = 0.81 10% and 40% are not statistically differentOrganosolv lignin Linear relationship between Linear regression of catalalysts loading versus yield of lignin monomers for organosolv lignin. catalyst loading and lignin yield The reaction conditions were: Residence time: 4 hours; temperature: 200 °C; pressure: 1000 psi; catalyst: 10% and 40% (w/w) of Pt/C; phosphoric acid: 40% (w/w); solvent: H 2O (1:1,v/v); feedstock: organosolv lignin.  Linear regression analysis statistically significant
  29. 29. Lignin Hydrogenolysis The effect of addition mineral acid on lignin hydrogenolysis Many reactions combine heterogeneous Phosphoric Acid Effect catalysis with acid-catalyzed conditions 50 to assist in the hydrogenolysis reaction No Phosphoric Acid (Yan et al., 2008) 40 Yes Phosphoric Acid Yield (% ,w/w)Poplar 30 The acid treatments were statistically different for lignin yield. 20 Presence of phosphoric acid 10 increased monomer yield  Assisted in the removal of 0 a recalcitrance of lignocellulose r pla OL PoOrganosolv lignin Feedstock The acid treatments were a Organosolv Lignin statistically different for lignin yield. Lignin product yield during catalytic hydrogenolysis with/without mineral acid on poplar and organosolv lignin. The reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; Presence of phosphoric acid Pressure: 1000 psi; catalyst: 10% (w/w); solvent: H2O (1:1,v/v); feedstock: poplar, organosolv lignin.. decreased monomer yield slightly.  Condensation reactions  Lignin condensation reactions under acidic conditions
  30. 30. Lignin Hydrogenolysis The effect of solvent on lignin Solvent effect on Poplar 60 hydrogenolysis Water/Ethanol (1:1,v/v) Ethanol Yield (%,w/w) 40 Water/Dioxane (1:1,v/v)Poplar Dioxane Water 20 The solvent treatments were 0 statistically different for lignin ne ol er v) ) /v an v/ at xa ,v 1, W :1 th io 1: (1 E D l( yield. e o n an xa th io /E /D er er at at W W Water as a solvent did not Solvent produce guaiacylpropane and a Values greater than theoretical value Lignin product yield during catalytic hydrogenolysis while varying solvent on poplar. The syringylpropane. reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) Pt/C; phosphoric acid: 40% (w/w);); feedstock: poplar. Water/ethanol (1:1, v/v) highest Solvent effect on Organosolv lignin yield 8 Ethanol Dioxane solvent produced the 6 Dioxane Yield (%,w/w) W ater lowest yield. 4 W ater/Dioxane (1:1, v/v) 2Organosolv lignin 0 The solvent treatments were not ne ol er ) /v an at xa ,v W th io :1 E D (1 e n statistically different for lignin xa io /D er at W yield. Solvent Lignin product yield during catalytic hydrogenolysis while varying solvent on organosolv lignin. Water as a solvent did not The reaction conditions were: Residence time: 4 hours; Temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) Pt/C; phosphoric acid: 40% (w/w);); feedstock: organosolv lignin.
  31. 31. Polysaccharides Hydrogenolysis Polysaccharides are degraded and converted concurrently with the depolymerization of lignin during hydrogenolysis Polysaccharides are converted into polysaccharide monomers, polysaccharide derived chemicals and insoluble liquid (solid residue)  Homolytic dissociation of H2 (g) into H atoms by noble metal catalysts  Influences hydrolysis  Spill-over effect  Cleavage of carbon-carbon and carbon-oxygen bonds in cellulose  Hydrogenation  Phosphoric acid  Hydrolysis (Dhepe and Fukuoka, 2007)
  32. 32. Polysaccharides Hydrogenolysis Changes of polysaccharides during hydrogenolysis  Liquid soluble products  Polysaccharide monomers and polysaccharide derived chemicals (PDCs)  Liquid insoluble products  Solid residue For avicel cellulose, 34% conversion of initial cellulose into polysaccharides and polysaccharides derived chemicals  ~6% polysaccharide monomers identified from original polysaccharides For poplar, 64% conversion of feedstock.  ~8% polysaccharide monomers Mass balance of cellulose hydrogenolysis. The reaction conditions were: Residence time: 4 hours; temperature: 200 °C; Pressure: 1000 psi; catalyst: 10% (w/w) of identified from original polysaccharides Pt/C; phosphoric acid: 40% (w/w); solvent: H2O (1:1,v/v); feedstock: cellulose. a theoretical weight of un-identifiable saccharides-derived chemicals. Reaction conditions produced statistically significant conversion percentages of polysaccharides  90-100% conversion of initial polysaccharides into PDCs and solid
  33. 33. Polysaccharides Hydrogenolysis Trace amounts of dehydration chemicals from glucose were detected  Glucose converted to HMF, furfural, levulinic acid, formic acid, acetic acid under hydrothermal conditions in the presence of acidic (Liu et al., 2011) conditions. Cellulose converted into polyols such as sorbitol through hydrogenation using supported metal catalysts  Previous experiments (Shrotri et al., Conversion products from catalytic hydrogenolysis of cellulose. (1) glucose, (2) 2012) sorbitol, (3) sorbitan, (4) isosoribde, (5) xylose, (6) erythritol, (7) glycerol, (8) 1,2- (or1,3)propanediol (9) ethanediol, (10) methanol. (Palkovits et al., 2010). Chemicals detected by
  34. 34. Summary Thermochemical conversion is capable of converting all three biopolymers in biomass into fuels and chemical precursors simultaneously.  Biochemical conversion inefficiently utilizes lignin Lignin derived chemicals and polysaccharide derived chemicals were fractionated with non-polar solvents. Lignin is selectively depolymerized into monomeric subunits for chemical precursors through catalytic hydrogenolysis  Syringylpropane  Guaiacylpropane  Reaction conditions affect the monolignol yield. Polysaccharides were degraded through hydrogenolysis  Polysaccharide monomers  Polysaccharide derived chemicals  No dehydration chemicals  Possible polyols production  Reaction conditions affect the degradation of polysaccharides
  35. 35. Future Research Further investigation of polysaccharide derived chemicals (PDCs) produced through hydrogenolysis  Accurate mass balance  No assumption necessary  Energy balance for viability of process Design of Experiment (DOE) methodology  Use factorial experimental designs  Determine interaction effects Investigation into other catalysts  Increase the selectivity  Decrease the activation energy
  36. 36. Acknowledgments Dr. Xuejun Pan  I am honored to have Dr. Pan as my mentor  He has given me a great deal of academic support in addition to assistance in my research study. Dr. Pan’s Research Group  There support and knowledge were vital in my research studies. Dr. Ralph’s Research Group  I need to thank Dr. John Ralph for allowing me to use his laboratory equipment.  Special thanks to Dr. Fachuang Lu for assistance in gas chromatography and mass spectrometry. Thesis committee  I need to thank Dr. Troy Runge and Dr. Fachuang Lu for accepting my invitation to be on my thesis committee  In addition to helping finalize my thesis. Biological Systems Engineering  For the departments support during my undergraduate and graduate studies.
  37. 37. Questions (Nagy et al., 2009)

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