The effect of acid pretreatment on bio-ethanol and bio-hydrogen production from sunflower straw

Transcription

1 nd International Conference on Sustainable Solid Waste Management The effect of acid pretreatment on bio-ethanol and bio-hydrogen production from sunflower straw G. Antonopoulou 1, G. Dimitrellos 1, D. Vayenas 1, and G. Lyberatos 1,3 1 Institute of Chemical Engineering Sciences, Stadiou 1, Platani, Patras,654, Greece Department of Environmental and Natural Resources Management, University of Patras,. G. Seferi st, Agrinio, GR31, Greece 3 School of Chemical Engineering, National Technical University of Athens, GR 1578 Athens, Greece

2 Sunflower straw (SS) Sunflower is the fourth oil-seed source worldwide with more than 5 million hectares cultivated land surface Sunflower has a high-lipid content seed and represents an important resource for biodiesel production. While it is mainly harvested for its oil, the remainder of the plant, such as the straw, remains to a large extent unutilized. Each hectare of sunflower culture could produce 3-7tons of dry biomass, including heads and stalks (Marechal and Rigal, 1999) In order to maintain a competitive advantage in the world market and ensure a sustained economic return in the production of this oil crop, the potential of conversion of this lignocellulosic residue in bioenergy should be explored and exploited.

3 Lignocellulosic biomass

4 Pretreatment Pretreatment is commonly accepted to be an essential prerequisite to make lignocellulosic biomass accessible to enzymatic attack, by breaking the lignin seal, removing hemicellulose, or disrupting the crystalline structure of cellulose (Fan et al., 1981) The correlation of structural features and digestibility is reported to be of variant importance according to the type of biomass to be treated Consequently, because of the heterogeneity of lignocellulosic biomass the application of the same pretreatment method can affect in a different degree and have an effect of different extent in different types of biomass. Best pretreatment method for intended bioconversion

5 Pretreatment A variety of pretreatment including mechanical, thermochemical or thermal processes, have been developed for changing the chemical and structural composition of biomass and improving the enzymatic conversion efficiency (Hendriks and Zeeman, 9). Acid pretreatment, has been proposed as an efficient pretreatment method for ethanol or fermentative hydrogen production (Schell et al., 3; Sanchez et al., 4; Garcia et al., 14) During acid pretreatment, hemicellulosic fraction of biomass is hydrolyzed to soluble sugars and compounds such as furfural and/or hydroxylmethylfurfural (HMF), formic and acetic acids can also be observed (Ramos, 3). These compounds might have an inhibitory or toxic effect on bacteria or yeasts that are used in subsequent bioconversions..

6 Biochemical processing Physical, chemical or biological pretreatment Simultaneous or separate saccharification and fermentation Pretreatment Enzymatic hydrolysis Fermentati on Distillation or separation Product(s) Solubilization of components Hydrolysis of cellulose by enzymes Biochemical conversion of sugars(hexoses and pentoses) to products) Solid residues & Wastewaters Cost efficient production of sugars from biomass is a key pre-requisite for any biorefinary based on sugar route.

7 The process followed. Simultaneous saccharification and fermentation (SSF) Acid Pretreatment Chemical agent Enzymatic hydrolysis Concentrati on (g/1gts) Fermentation Conditions Η SΟ 4, 1, 1h, 1 o C Η 3 PΟ 4, 1, 1h, 1 o C HCl, 1, 1h, 1 o C no chemical thermal 1h, 1 o C Ethanol Hydrogen Solubilization of hemicellulose Hydrolysis of cellulose by enzymes Biochemical conversion of sugars(hexoses and pentoses) to products) For all pretreatment methods: mass ratio of solid(g) to liquid(ml) was 5:1 (organic load 5% w/v)

8 Why hydrogen? A clean and environmentally friendly fuel which produces water instead of greenhouse gases, when combusted Possesses a high-energy yield (1 kj/g) Could be directly used to produce electricity through fuel cells cells Can be produced by renewable raw materials, such as wastes / wastewaters and energy crops through biological processes

9 Fermentative hydrogen production Acetic acid production C 6 H 1 O 6 + H O CH 3 COOH + CO + 4H Butyric acid production C 6 H 1 O 6 CH 3 CH CH COOH + CO + H Propionic acid production C 6 H 1 O 6 + H CH 3 CH COOH + H O Lactate production C 6 H 1 O 6 CH 3 CHOHCOOH Ethanol production C 6 H 1 O 6 CH 3 CH OH + CO Mixed acid fermentations lower yields of H The absence or presence of hydrogen-consuming microorganisms in the microbial consortium also affects the microbial metabolic balance Mixed cultures need to be pretreated in order to suppress hydrogen-consuming bacterial activity while still preserving the activity of the hydrogen-producing bacteria Heat treatment (1 o C, 15min)

10 Bioethanol production The production of bioethanol from traditional means, or 1 st generation bioethanol is based upon starch crops (corn and wheat) and from sugar crops (sugar cane and sugar beet) It could be used as transport fuel (blended with petrol at 5%). A wide range of uses in the pharmaceuticals, cosmetics, beverages and medical sectors Although cellulose can be efficiently hydrolyzed to glucose and then fermented to ethanol, xylose and other C 5 sugars, released during hemicellulose hydrolysis, are much more difficult to be efficiently fermented (Jeffries, 6). Bioconversion of both C 5 and C 6 sugars to ethanol is one of the most important issues to make bioethanol as a commercially viable product. Pichia stipitis is reported to be the most efficient and highly productive strain for significant ethanol production from xylose (Cheng et al., 8).

11 Chemical composition Characteristic Value ΤS (%) 9.9 ±.4 VS (%TS ±.9 Cellulose (%TS) 7.79 ±.57 Hemicellulose (%TS) ±.37 Lignin (%TS).34±.6 Ash (%TS) 1.9±.56

12 Chemical composition after pretreatment Pretreatment no thermal Η SΟ 4 g/1gts 1 g/1gts g/1gts Η 3 PΟ 4 g/1gts 1 g/1gts g/1gts HCl g/1gts 1 g/1gts g/1gts Cellulose (g/1gts) Hemicellulose (g/1gts) 8.49 ± ± ± ± 1. Lignin (g/1gts).11 ± ± ± ± ± ± ±.8.78± ± ± ± ± ±.6.6 ± ± ± ± ± ± ± ± ± ± ± ± ±.56

13 g/l g/l Chemical composition after pretreatment Pretreatment no raw thermal Η SΟ 4 g/1gts 1 g/1gts g/1gts Η 3 PΟ 4 g/1gts 1 g/1gts g/1gts HCl g/1gts 1 g/1gts g/1gts Sugars (g/1gts).71 ±.16.8 ± ± ± ±.1.78 ± ±.1 5.3±.6.87± ± ±.1 1,5 1,5 1,5 furfural HMF formic acid acetic acid Treatment with HCl of 1 and g/1gts and H SO 4 at g /1gTS, led to higher hemicellulose solubilisation and higher furfural and HMF concentration values The higher the acid concentration, the higher the HMF and furfural which was produced (Hendriks, and Zeeman, 9).

14 Fermentative hydrogen production 16 ml serum vials Headspace Inoculum (%v/v) Biogas measurement Hydrogen content Inoculum: Anaerobic sludge from the anaerobic digester of Patras wastewater treatment plant: boiled for 15min at 1 o C Assays: In 16mL serum bottles, at 35 o C: 1mL inoculum + 3mL synthetic medium + 1mL whole pretreated biomass (. 5gTS SS + 1 ml of each chemical agent) 5% organic load Mixture of Celluclast 1.5L + Novozyme at a ratio of 3:1, (3FPU Celluclast/gTS) Cellulase from Trichoderma reesei, ATCC 691 Cellobiase from Aspergillus niger Agitation at 1rpm at 35 o C

15 Fermentative hydrogen production 15 HCl (g/1gts) 15 H SO 4 (g/1gts) 15 H 3 PO 4 (g/1gts) H (L /kgts) 1 5 H (L/kg TS) 1 5 H (L /kg TS) 1 5 raw raw-ssf 1 raw raw-ssf 1 raw raw-ssf 1 Treatment with HCl and H SO 4 of 1g/1gTS and H 3 PO 4 of g/1gts led to higher hydrogen yields. Treatment with HCl 1g/1gTS caused a 159% increase when compared with the untreated sample (in a SSF concept- 6.4L/kg TS). Concentration of HCl and H SO 4 of g/1gts caused an inhibition to hydrogen production microorganisms.

16 Fermentative hydrogen production 3 acetate propionate butyrate 3 acetate propionate butyrate 3 acetate propionate butyrate 5 HCl (g/1gts) 5 H SO 4 (g/1gts) 5 H 3 PO 4 (g/1gts) g/kgts 15 1 g/kgts 15 1 g/kgts raw raw-ssf 1 raw raw-ssf 1 raw raw-ssf Higher hydrogen yields were correlated H SO 4 (g/1gts) to higher butyrate production 6 (Antonopoulou et al., 8). ph 5 C 6 H 1 O 6 CH 3 CH CH COOH + CO + H HCl (g/1gts) raw raw-ssf 1 ph raw raw-ssf 1 ph 6 H 3 PO 4 (g/1gts) raw raw-ssf 1

17 Ethanol fermentation experiments Pichia Stipitis (strain CECT 19) Solution (g/l): KH PO 4, (1) MgCl *6H O, (1) (NH 4 ) SO 4, (1) C5 and C6 sugars uptake Main metabolic products: Ethanol -xylitol The whole pretreated biomass (.75gTS SS + 15 ml of each chemical agent) 5% organic load Mixture of Celluclast 1.5L + Novozyme at a ratio of 3:1, (3FPU Celluclast/gTS) Cellulase from Trichoderma reesei, ATCC 691 Cellobiase from Aspergillus niger Adjustment of initial ph at 5 Agitation at 1rpm at 3 o C Fermentation for 48h

18 Ethanol fermentation experiments 1 g/l Glucose Ethanol.8 g ethanol/g glucose 1.8 mol ethanol /mol glucose C 6 H 1 O 6 CH 3 CH OH + CO Time (h) 1 54 % of maximum theoretical g/l Xylose Ethanol.8 g ethanol/g xylose.91 mol ethanol /mol xylose 3C 5 H 1 O 5 5CH 3 CH OH + 5CO +5 HO Time (h) 55 % of maximum theoretical

19 Ethanol fermentation experiments Ethanol (g /kg TS) HCl (g/1gts) Ethanol (g/kg TS) HSO4 (g/1gts) Ethanol (g/kg TS) H3PO4(g/1gTS) raw-ssf 1 raw-ssf 1 raw-ssf 1 Treatment with HCl and H 3 PO 4 of g/1gts led to higher ethanol yields. Concentration. of g Hethanol/g SO 4 of g/1gts initial carbohydrates caused an inhibition to P.stipitis. 78% of the maximum obtained

20 Conclusions Acid pretreatment could be used to enhance hydrogen and ethanol production from SS The optimum, for hydrogen production, pretreatment method, was not the optimum for ethanol production, implying that the same pretreatment method is not appropriate for all subsequent bio-conversion processes. Pretreatment with HCl seems to be more effective. HCl at 1g/1gTS led to LH/kg TS while HCl at g/1gts led to 17 g ethanol/kg TS. Higher hydrogen yields were correlated to higher butyrate production Pretreatment with HSO4 at g/1gts led to higher furfural and HMF concentration and led to lower ethanol and hydrogen production yields.

21 Thank you very much! General Secretariat for Research and Technology Supporting Postdoctoral Researchers Projects - Pretreatment of lignocellulosic wastes for nd generation biofuels (POSTDOC _ PE8(1756)) (post-doc fellowship of Dr. G. Antonopoulou).