Optimization of bio-oil yields by demineralization of low quality biomass

1. Chemical Process & Energy Resources Institute (CPERI) Centre for Research and Technology Hellas (CERTH) Optimization of bio-oil yields by demineralization of low quality biomass Dr. Angelos A. Lappas Research Director CPERI/CERTH 570 01 Thermi Thessaloniki, Greece International Congress and Expo on Biofuels & Bioenergy August 25-27, 2015 Valencia, Spain

2. OUTLINE • Introduction • Materials and Methods • Biomass samples and characterization • Biomass pretreatment methods • Pyrolysis tests • Results and Discussion • Characterization of biomass samples • Preliminary demineralization results • Demineralization of different biomass types • Pyrolysis tests results • Chemical composition of the bio-oil • Conclusions

3. INTRODUCTION • Fast pyrolysis is an important thermochemical process for the conversion of biomass to a high added value liquid products (fuels & chemicals) • Minerals (ash) in biomass: • act catalytically during fast pyrolysis reducing biooil yield • catalyze chemical reactions during storage of biooil affecting biooil quality • deactivate the catalysts in biomass catalytic pyrolysis and/or in downstream biooil catalytic upgrading processes • Use of low cost-high ash feedstocks (agricultural residues and energy grasses) is important for the pyrolysis process economics • A strategy for process optimization is to remove the inorganics prior to pyrolysis • Inorganics can be removed by water washing, acid washing and size reduction Objectives of this study : i) to investigate the water and acid washing as biomass pre-treatment techniques for the removal of inorganics from 6 different biomass types ii) to examine how inorganics removal affects pyrolysis product yields

4. EXPERIMENTAL Biomass samples: • a reference commercial lignocellulosic biomass from beech wood • two forestry residues (oak and pine wood) • two agricultural residues (wheat and barley straw) and • two energy crops (miscanthus and eucalyptus) Pre-treatment: • Particle size: 90-500 μm. • 4 g of biomass dissolved in 80 ml water/acid under stirring • Parameters investigated: T (ambient, 50°C), residence time (2, 4, 8 and 24 h), type of acid (acetic vs nitric), acid concentration Pyrolysis: • Pyrolysis experiments were carried out on a bench-scale, fixed-bed reactor • Mass balances and product characterization were carried out for all tests

5. RESULTS AND DISCUSSION

6. CHARACTERIZATION OF BIOMASS SAMPLES Inorganics by ICP analysis (ppm, dry basis) • K, Ca, Na and Mg are the most abundant inorganic elements. • Comparing a low ash (pine), with a high ash content feedstock (barley), a ten-fold increase in alkali concentration may be noted.

7. PRELIMINARY DEMINERALIZATION RESULTS WITH REFERENCE FEED • Ash removal with H2O 25% (20°C), 43% (50°C) • Much higher de-ashing with acids • Water is adequate for removal of water-soluble metal salts but not for the cations • Nitric is better than acetic acid while higher acid concentrations are preferable • Effect of treatment time not very pronounced • Higher temperatures favor when acid concentration is low Optimum Conditions • Acid concentration = 1 wt% • Residence time = 2 h (acid), 4 h (H2O) • Washing temperature = 50°C • Acids (Nitric, Acetic)

8. DEMINERALIZATION OF ALL BIOMASS TYPES • Washing with acids more efficient compared with water (90% vs. 17-43%) • Nitric more effective than acetic acid • Ash removal from forestry residues higher than with the other biomass samples • The agricultural residues exhibited relatively high ash content, even after treatment with nitric acid • Satisfactory ash removal was achieved for eucalyptus (up to 70%) while miscanthus was much harder to treat (up to 40% ash removal) • The loss of biomass depends more on the biomass type, rather on pre-treatment conditions. Agricultural residues demonstrated the highest weight loss

9. ASH REMOVAL FOR EACH ELEMENT • Alkali metals, K and Na easily removed (>80% with all pre-treatment methods • Removal of Mg, Fe and Al was lower, following the order Mg > Fe > Al • Ca most affected by the treatment method and its removal increased in the order nitric acid > acetic acid > water treatment • Treatment with nitric acid the most efficient for all inorganics and all biomass types

10. EFFECT OF DE-ASHING (1% HNO3) ON PYROLYSIS PERFORMANCE • Bio-oil yield increases on all de-ashed samples, The effect being higher ~17% for agricultural residues • For the demineralized samples, gas yield is about 4-8 wt% lower • Most of this reduction was attributed to the reduction of the CO2 yield • Char formation also decreased, especially in the case of wheat straw, barley straw, eucalyptus and miscanthus

11. CATALYTIC MECHANISMS Thermal decomposition of cellulose in the absence of inorganics Scission of the o-glucosidic bonds Cellulose Levoglucosan Thermal decomposition of cellulose in the presence of inorganics Metal cations act as catalysts Δ Homolysis of the pyranose rings Cellulose Formation of CO2,carbonyls and acids Levoglucosan C.-Y. Yang, X.-S. Lu, W.G. Lin, X.-M. Yang, J.Z. Yao, Chem Res Chinese U 22 (2006) 524–532

12. GCxGC-ToFMS ANALYSIS OF BIO-OIL • Bio-oil from treated biomasses contains anhydrosugars and more specifically, levoglucosan • In the bio-oil from the untreated biomasses anhydrosugars are very low and furans, ketones and ethers increase. • Phenolics decrease in bio-oils after demineralization • This indicates that inorganics catalyze cracking of the lignin structure and oligomers, resulted in the formation phenolic monomers

13. CONCLUSIONS • Removal of ash from forestry residues, agricultural residues and energy crops was studied in this work: • Washing with water removed up to 42% of the inorganics whereas washing with acidic solutions achieved higher than 90% removal • Higher washing temperatures were more effective for the removal of the inorganics. • Nitric acid proved to be more effective than acetic acid. • K, Na can easily be removed by all pre-treatment methods • Mg, Fe and Al are more refractory • Ca is affected by the pretreatment conditions and mainly is removed by nitric acid solution • Biomass demineralization affects strongly yields and composition of the pyrolysis products • demineralized biomass yielded less gas products and solid residue while the selectivity towards the liquid product was substantially increased • Biooil from de-ashed biomass contains more levoglucosan levels and is less deoxygenated The work was conducted with support from the EU under the frame of the FP7 funded “CAScade deoxygenation process using tailored nanoCATalysts for the production of BiofuELs from lignocellullosic biomass – CASCATBEL” project (Grant agreement No. 604307).