Assessing Cellulose Accessibility of Lignocellulosic Biomass before and after Pretreatment

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1 Assessing Cellulose Accessibility of Lignocellulosic Biomass before and after Pretreatment Xianzhi Meng 1, Marcus Foston 1, Jaclyn DeMartini 2, Charles E. Wyman 2 and Arthur J. Ragauskas 1,3 (1) BioEnergyScience Center, School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA (2) BioEnergyScience Center, Department of Chemical & Environmental Engineering, Center for Environmental Research and Technology, University of California, Riverside, CA (3) Institute of Paper Science and Technology at Georgia Institute of Technology, Atlanta, GA

2 utline 1. verview of biomass recalcitrance 2. Analytical techniques used to evaluate cellulose accessibility and Results Simons Stain for estimating available surface area 1 H NMR cryoporometry for determination of pore size distribution 3. Summary 2

3 Biomass Recalcitrance Lignocellulosic biomass is often described as recalcitrant. Crystalline cellulose, hydrated hemicellulose, and lignin Exhibit differential reactivity to thermal, chemical, and biological processing 3 US DE Genomics:GTL Roadmap, DE/SC- 0090, U.S. Department of Energy ffice of Science

Saccharification Biomass Sugar Fermentation Ethanol Hemicellulose Dilute acid, steam

4 Pretreatment can vercome the Natural Recalcitrance of Biomass Biochemical conversion of cellulosic biomass to ethanol Biomass Feedstock Pretreatment Enzymatic Cellulose Saccharification Biomass Sugar Fermentation Ethanol Hemicellulose Dilute acid, steam explosion, organosolv, ammonia fiber explosion.. Lignin Cellulose 4

5 bjectives and Analytical Techniques Used in This Study Assess cellulose accessibility Effectiveness of pretreatment vercome biomass recalcitrance Determination of available surface area of native and pretreated Poplar by a Simons Stain technique. 1 Measurement of pore size distributions by NMR cryoporometry. 2 1 The characterization of pretreated lignocellulosic substrates prior to enzymatic hydrolysis part 1: a modified Simons staining technique (2008). Biotechnol Progr 24: Chandra RP, Eeanick S, Hsieh C, Saddler JN. 5 2 Porosity and its effect on the digestibility of dilute sulfuric acid pretreated corn stover (2007).J.Agric. Food Chem. 55, Ishizawa C, Davis, FM,Schell DF, Johnson DK.

6 Constitution of Simons Stain Direct Blue 1 Direct range 15 Well-defined chemical formula: C 34 H 28 N 6 16 S 4 Molecular diameter: 1 nm Low affinity for cellulose Condensation product of 5-nitrotoluenesulfonic acid in aqueous alkali. Molecular diameter: 5-36 nm High affinity for cellulose NH 2 H H NH 2 Na Na Na Na S N N N N S Na S S S S CH 3 CH 3 S N N C H C H S N N Na Na Na n >61 6

7 Mechanism of Simons Stain Measure of accessibility of the interior surface to the dyes Blue dye: small molecular size, low affinity for cellulose range dye: large molecular size, high affinity for cellulose range : Blue = 1:4 range : Blue = 3 : 2 7

8 Poplar Pretreatment Conditions Pretreatment Temp/ o C Time/ Min H 2 S 4 / M Dilute Acid Steam Explosion Untreated Poplar Steam Exploded Poplar 8 10 min DAP Poplar 60 min DAP Poplar

9 72 h Cellulosic Conversion % Simons Stain and Enzymatic Hydrolysis Results Substrate (Poplar) Maximum Adsorbed range Dye (mg/g) Maximum Adsorbed Blue Dye (mg/g) range: blue (/B) 24 h Cellulose Conversion (%) 48 h Cellulose Conversion (%) As /B increases, cellulose conversion increases 72 h Cellulose Conversion (%) Untreated steam explosion min DAP min DAP Simons Stain a effective diagnostic tool to evaluate the cellulose accessibility As total adsorbed dye increases, cellulose conversion also increases Total Adsorbed Dye on Fiber (mg/g) 9 The linear relation between total dye adsorption during the modified Simons stain measurement and the 72 h cellulose conversion yield (%) during enzymatic hydrolysis. (R 2 = 0.94)

10 Analytical Techniques used in this study Determination of available surface area of native and pretreated Poplar by a Simons Stain technique. 1 Measurement of pore size distributions by NMR cryoporometry. 2 1 The characterization of pretreated lignocellulosic substrates prior to enzymatic hydrolysis part 1: a modified Simons staining technique (2008). Biotechnol Progr 24: Chandra RP, Eeanick S, Hsieh C, Saddler JN Porosity and its effect on the digestibility of dilute sulfuric acid pretreated corn stover (2007). J.Agric. Food Chem. 55, Ishizawa C, Davis, FM,Schell DF, Johnson DK.

11 Background NMR Cryoporometry NMR cryoporometry Non-destructively determine of pore size distributions Melting point depression Silica gels, rocks, corn stover The spin-echo intensity as a function of the temperature for four silica-gels Gibbs Thomson equation: ΔT = Tm Tm(x) = K / x Melting point depression inversely proportional to pore size Strange, J.H.; Rahman, M.; Smith, E.G., "Characterization of Porous Solids by NMR", Phys. Rev. Lett. 71 (21):

12 1 H NMR Spectra of 60 min DAP Poplar From -50 o C to 5 o C 5 0 C 0 0 C C C C nly unfrozen water contributes to signal intensity Intensity increases as temperature increase Changes of intensity reflects pore size distribution 1 H NMR spectra of 60min DAP poplar from C to 5 0 C C C C C 12

13 Pore size distribution determined by NMR Cryoporometry Pore size distribution determination dv/dx = dv/dtm(x) dtm(x)/dx ΔT = Tm Tm(x) = K / x, so dtm(x)/dx = k/x 2 Therefore, dv/dx = dv/dtm(x) k/x 2 a) An ideal NMR cryoporometry melting curve with four main features: (1) pore melting step; (2) total pore volume plateau; (3) bulk melting step, and (4) total liquid volume plateau (b) The pore distribution derived from the melting curve 13 Mitchell, J.; Webber, J. Beau W.; Strange, J.H. (2008), "Nuclear Magnetic Resonance Cryoporometry", Phys. Rep. 461: 1 36

14 PSD (a.u.) Pore Size Distribution Curves for Untreated and Pretreated Poplar Untreated min Steam explosion min DAP min DAP Pore diameter (nm) 14

15 Summary Simons Stain Cellulose Accessibility NMR cryoporometry Effective and valuable diagnostic tools to evaluate cellulose accessibility & effectiveness of pretreatment 15 Pretreated Poplar As severity factor extend For condition studied (160 o C, 10min) Larger accessible surface area Higher cellulose conversion Increase accessible surface area DAP much more effective than Steam Explosion

16 THANK YU! Funding support BESC (BioEnergy Science Center)

17 Conventional Simons Stain Technique Very time consuming 2 days incubation time 18 hours dye-stripping step using pyridine Can not calculate the maximum amount of dye adsorbed Question: Eliminate the dye-stripping step? Decrease the incubation time? Calculate the maximum amount of dye adsorbed? 17

18 A Modified Simons Stain Technique Use of UV-vis spectroscopy eliminates dye-stripping step Successfully decrease the incubation time (48 h to 6 h) Use of langmuir isotherm equation allows the calculation of maximum amount of dye (a). FBK: fully bleached kraft fiber UK: unbleached kraft pulp fiber TMP: thermomechanical pulp fiber SP: steam pretreated pine E: Ethanol-organosolv pretreated pine (b) Both /B ratio and total amount of dye adsorbed are strong indicators of the distribution of pores The characterization of pretreated lignocellulosic substrates prior to enzymatic hydrolysis part 1: a modified Simons staining technique (2008). Biotechnol Progr 24: Chandra RP, Eeanick S, Hsieh C, Saddler JN 18 (a). The measurement of various lignocellulosic substrates using Simons Stain (b). The linear relation between total dye adsorption during Simons Stain and the 24 h cellulose conversion

19 Determination of Amount of Dye Adsorbed by UV-vis Measurement Amount of dye adsorbed = Initial dye - Remaining dye A 455nm = ε /455 L C + ε B/455 L C B A 624nm = ε /624 L C + ε B/624 L C B Lambert-Beer law for a binary mixture A: absorption at 450 or 624 nm ε: extinction coefficient L: path length C /B: concentration of remaining dye Simultaneously solved 19

20 Determination of Maximum Amount of Dye Adsorbed Maximum amount of dye adsorbed Intercept = 1/[A] max Langmuir isotherm 1/[A] = 1/[A] max + 1/K ads [A] max [C] [C]: concentration of free dye [A]: amount of dye adsorbed [A] max : maximum adsorbed dye K ads : adsorption constant 1/[A] versus 1/[C] Dye adsorption curves 20

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