Bio-oil derived from fast pyrolysis of lignocellulosic materials is among the most complex and inexpensive raw oils that can be produced today. Although commercial or demonstration scale fast pyrolysis units can readily produce this oil, this industry has not grown to significant commercial impact due to the lack of bio-oil market pull. This paper is a review of the challenges and opportunities for bio-oil upgrading and refining. Pyrolysis oil consists of six major fractions. (water 15-30 wt.%, light oxygenates, 8-26 wt. %, mono-phenols, 2-7 wt.%, water insoluble oligomers derived from lignin 15-25wt.%, and water soluble havey molecules 10-30 wt.%). The composition of water soluble oligomers is relatively poorly studied. In the 1880s bio-oil refining (formally known as wood distillation) targeted the separation and commercialization of C1-C4 light oxygenated compounds to produce methanol, acetic acid and acetone with the commercialization of the lignin derived water insoluble fraction for preserving purification techniques. Strategies for biofuels production are discussed in section four. Bio-oil derived products are discussed in the last section. 2. Bio-oil Composition The study of bio-oil chemical composition has been the subject of active research in the last twenty years 2,24-35. Pyrolysis oil contains numerous oxygenated compounds, which include carboxylic acids, water, alcohols, esthers, anhydrosugars, furanics, phenolics, aldehydes, and ketones covering a wide range of molecular weights and functionalities 2,24,29,30,36-41. The specific composition is directly related to the feedstock and the conditions used in their production 42-44. Water is typically quantified by Karl Fischer titration 2 and is the most abundant bio-oil compound accounting between 15 and 30 wt. % 2 (See Figure 1). Water forms mostly from dehydration reactions of carbohydrate depolymerized products in the liquid intermediate 44. Gas Chromatography/Mass Spectroscopy (GC/MS) is by far the most common technique for the quantification of the pyrolysis oil organic volatile fraction 2,24,27,45. GC/MS detectable compounds typically account for between 30 and 40 wt. % 2. Table 2 shows the range of compounds quantified by GC/MS reported in the literature. Only four molecules (glycoaldehyde, acetic acid, acetol and levoglucosan) are found in quantities sufficiently high (>5 wt. %) to justify their separation and commercialization as chemicals. Methanol can also be produced in quantities justifying its commercialization but hardwood has to be used as feedstock. The remainder of the oil if refined is likely to be commercialized as fractions (mono-phenols, pyrolytic lignin, anhydrosugars, pyrolytic humins, and hybrid oligomers). Because bio-oil consists of hundreds of compounds with concentrations below 0.5 wt. % it is desirable to express their chemical composition in terms of few chemical groups or families 24. This idea was first proposed by Hallet and Clark 46. The authors 46 modeled bio-oil evaporation rates using a model based on this characte...

Four principal intra-particle phenomena occur in a highly concerted manner during the pyrolysis of lignocellulosic materials: heat transfer, mass transfer, chemical reactions, and phase changes.

A new methodology has been proposed to describe of the dynamics of bubble formation during pyrolysis of Organosolv lignin and sucrose (surrogates for biomass) using fast speed visualization (125fps) with mathematical modeling. The model uses a population balance to predict overall rates of bubble birth and death, bubble bursting, and aerosol ejection. The experimental studies were performed on a uniquely modified CDS Analytical Pyroprobe 5000 to visualize the formation of bubbles within the liquid intermediate phase at heating rates close 100 o C/s. Experimentally, we observed that bubbles follow a log-normal distribution versus bubble size within the liquid intermediate phase for both materials. This distribution function changes over time due to increased viscosity from solidification reactions that generate char and the changes in the rate of bubble formation. Micro-explosion intensity was used to estimate aerosol ejection intensity. The model predicts aerosol ejection yields of 21.18% w / w from Organosolv lignin and 17.40% w / w from sucrose during pyrolysis with an average droplet size of 10 m.

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This paper reports studies on the film pyrolysis of sugarcane bagasse in an electrically heated hot plate reactor. The new experimental set up used is described. The bagasse studied was ground to particle sizes less than 37 µm (mesh 400) and was mixed with water to form the paste to be used to form the biomass film (10 mg of sugarcane bagasse distributed evenly on a steel plate, 60 µm thick). All the tests were conducted under vacuum (150 mbar). The effect of heating rate (between 5 and 1200 °C/s) and final temperatures (between 250 and 650 °C) on product yields (permanent gases, water, light volatile, pyrolytic lignin, sugars and char) were studied. The yield of fragmentation and dehydration products increased as heating rates augment. The effect of heating rate is only important till 100 °C/s, no significant changes in product yields are observed at higher heating rates. Bio-oils enriched in lignin and sugars oligomers were obtained at high temperatures and heating rates. These results suggest that good yields of fermentable sugars may be obtained in pyrolysis reactors working at intermediary pyrolysis conditions.

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a b s t r a c tPyrolysis of lignocellulosic materials typically form carbonaceous residues (chars) with structures similar to the starting material. However, previous studies reported in the literature have shown that fast pyrolysis of cellulose and lignin form a molten intermediate liquid resulting in chars with smooth surfaces and evidences of intense bubbling. The fraction responsible for morphology conservation during pyrolysis is not known. In this article, pyrolysis visualization studies were carried out with a fast camera on cellulose, xylan, Organosolv lignin (OL), milled wood lignin (MWL), and lignocellulosic sugarcane bagasse to identify the component responsible for morphological conservation. The materials were heated using a modified Pyroprobe with measured sample heating rates close to 100 • C/s. Our studies confirm that cellulose, lignin, and deashed xylan are completely transformed into an intermediate liquid; the intensity of bubbling for lignin was far superior that of cellulose. Xylan as received, however, only forms a small amount of intermediate liquid; it does not fully melt and maintains its general shape during pyrolysis. These results suggest that the presence of mineral matter is critical for lignocellulosic materials to retain their original morphology. We repeated the studies on raw bagasse and acid washed bagasse. The raw bagasse retains its morphology; the acid washed bagasse shrank dramatically, but was not completely converted into a liquid. Our results suggest that in addition to hemicellulose with the presence of ash, other biomass fractions or the different temperatures at which the different fractions melt and solidify could also be contributing to maintain the structure of the lignocellulosic material during pyrolysis.