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Production and Recovery of Pyrolytic Sugars

BEI’s thermochemical program conducts research into the production and recovery of pyrolytic sugars. Here is a listing of some of our more significant published papers in this area. Click on title to view article in a new window from the publication Website.

Rollag, S. A., Lindstrom, J. K., Brown, R. C. (2020) Pretreatments for the continuous production of pyrolytic sugar from lignocellulosic biomass, accepted for publication in Chemical Engineering.

Fast pyrolysis of lignocellulosic biomass yields little sugar or anhydrosugars compared to pyrolysis of pure polysaccharides because naturally abundant alkali and alkaline earth metals (AAEM) in biomass catalyze the fragmentation of pyranose and furanose rings. Sugar yields can be increased dramatically by pretreating the biomass with sulfuric acid prior to pyrolysis, which passivates the catalytic activity of the metals by converting them into thermally stable salts. However, depolymerization of lignin in biomass also depends on the catalytic activity of AAEM. Thus, passivating AAEM has the unintended consequence of slowing the rate of depolymerization and volatilization of lignin, resulting in a transient melt phase that agglomerates and can foul pyrolysis reactors.

To overcome this problem, various non-alkali metal sulfates were tested as replacements for sulfuric acid. Iron in the form of ferrous sulfate proved the most effective in depolymerizing lignin without fragmenting pyranose rings. Conventional nitrogen-blown pyrolysis of ferrous sulfate pretreated corn stover achieved WHSV of 4 h-1 compared to only 0.6 h-1 for acid pretreated corn stover. Autothermal (air-blown) pyrolysis of ferrous sulfate pretreated corn stover showed even more dramatic improvement, increasing WHSV from 1 h-1 to 10 h-1 compared to acid pretreated corn stover under autothermal operation. Fermentable sugar yields from the pyrolysis of corn stover increased from 0.9 wt% to 11.8 wt% on a biomass basis, a 13-fold increase as a result of the ferrous sulfate pretreatment. These advantages combine to increase volumetric sugar productivity from 62 g L-1 h-1 for conventional pyrolysis of untreated corn stover to 2041 g L-1 h-1 for autothermal pyrolysis of ferrous sulfate treated corn stover.

Rover, M. R., Aui, A., Wright, M. M., Smith, R. G., Brown, R. C. (2019) Production and purification of crystallized levoglucosan from pyrolysis of lignocellulosic biomassGreen Chemistry 21, 5980-5989.

Levoglucosan has significant potential in commercial applications for the synthesis of polymers, solvents and pharmaceuticals. It is currently overlooked for commercial applications due to its high cost of synthesis and purification. We have developed a system to produce pure crystals of levoglucosan based on the fast pyrolysis of lignocellulosic biomass. A novel bio-oil recovery system concentrated levoglucosan along with other anhydrosugars, sugars and phenolic compounds in a non-aqueous “heavy ends” fraction. Liquid–liquid water extraction separated sugar-rich solubilized carbohydrates from non-soluble phenolic compounds. The solubilized carbohydrate fraction, contaminated with partially soluble phenolic monomers, was filtered through Sepabeads SP207 adsorption resin to produce clarified juice. The composition of the clarified juice on a dry basis after resin filtration and rotary evaporation was 81.2% sugars, 4.45–4.60% volatile non-sugar, 1.71% carboxylic acids and 12.5–12.6% unidentified compounds, which was sufficiently pure to crystallize the sugars by evaporation. A cold solvent rinse of the crystal mass separated and purified levoglucosan from other sugars. Levoglucosan purity was 102.5% ± 3.109% at the 99% confidence level. Techno-economic analysis of a plant pyrolyzing 250 tonne per day of pretreated biomass to produce cellulosic sugars indicated a minimum selling price (MSP) for pure levoglucosan crystals of $1333 per MT, which is less than one-tenth its current average market price. Operating hours of the plant, fermentable syrup yield and fixed capital are the most significant parameters affecting MSP.

Lindstrom, J. K., Proano-Aviles, J., Johnston, P. A., Peterson, C. A., Stansell, J. S., Brown, R. C. (2019) Competing Reactions Limit Levoglucosan Yield during Fast Pyrolysis of CelluloseGreen Chemistry 21, 178-186.

Efforts to understand the reaction mechanisms of cellulose pyrolysis have been stymied by short reaction times and difficulties in probing the condensed phase of cellulose intermediate products. Using time-resolved yields of both volatile and non-volatile products of pyrolysis, we demonstrate that cracking reactions generate anhydro-oligosaccharides while subsequent reactions produce levoglucosan from these anhydro-oligosaccharides. Eventually, cracking of anhydro-oligosaccharides is eclipsed by levoglucosan-producing reactions. These reactions compete with other reactions that produce light oxygenates and non-condensable gases. The relative reaction rates in this competition limit levoglucosan yields from cellulose pyrolysis to approximately 60 wt%.

Patrick Johnston and Robert C. Brown (2014). Quantitation of Sugar Content in Pyrolysis Liquids after Acid Hydrolysis Using High-Performance Liquid Chromatography without Neutralization, Journal of Agricultural and Food Chemistry 62, 8129-8133.

Scientific diagram.

A rapid method for the quantitation of total sugars in pyrolysis liquids using high-performance liquid chromatography (HPLC) was developed. The method avoids the tedious and time-consuming sample preparation required by current analytical methods. It is possible to directly analyze hydrolyzed pyrolysis liquids, bypassing the neutralization step usually required in determination of total sugars. A comparison with traditional methods was used to determine the validity of the results. The calibration curve coefficient of determination on all standard compounds was >0.999 using a refractive index detector. The relative standard deviation for the new method was 1.13%. The spiked sugar recoveries on the pyrolysis liquid samples were between 104 and 105%. The research demonstrates that it is possible to obtain excellent accuracy and efficiency using HPLC to quantitate glucose after acid hydrolysis of polymeric and oligomeric sugars found in fast pyrolysis bio-oils without neutralization.

DiagramDustin L. Dalluge, Tannon Daugaard, Patrick Johnston, Najeeb Kuzhiyil, Mark M. Wright, and Robert C. Brown (2014). Continuous Production of Sugars from Pyrolysis of Acid-Infused Lignocellulosic BiomassGreen Chemistry 2014.16, 4144-4155.

Although pyrolysis of carbohydrate-rich biomass should theoretically yield large amounts of sugar, the presence of alkali and alkaline earth metals (AAEMs) in most biomass prevents this from happening. Even in small amounts, AAEM strongly catalyzes the fragmentation of holocellulose to light oxygenates compared to the thermally-induced breaking of glycosidic bonds that yield anhydrosugars. The concept of AAEM passivation, by which the catalytic activity of AAEMs can be suppressed to enhance thermal depolymerization of lignocellulose to sugars, has been previously established at the microgram scale using batch reactors. The feasibility of increasing sugar yield via AAEM passivation has not been previously demonstrated at the kilogram scale in a continuous flow reactor. The goal of this research is to demonstrate the enhanced production of sugars from AAEM passivated feedstocks in a continuous auger pyrolyzer at the kilogram scale. Alkali and alkaline earth metal passivation prior to pyrolysis increased total sugars from red oak by 105% compared to conventional pyrolysis, increasing from 7.8 wt% to 15.9 wt% of feedstock. Light oxygenates and non-condensable gases (NCGs) simultaneously decreased 45%, from 27.1 wt% to 14.7 wt% of feedstock as a result of AAEM passivation. Similarly, AAEM passivation of switchgrass increased total sugars by 259%, from 4.5 wt% to 16.2 wt% of feedstock, while the light oxygenates and NCGs decreased by 48%, from 20.0 wt% to 10.5 wt% of feedstock. An undesirable outcome of AAEM passivation was an increase in char production, increasing by 65% and 30% for pyrolysis of red oak and switchgrass, respectively. Loss of lignin-derived phenolic compounds from the bio-oil can explain 67% and 38% of the increase in char for red oak and switchgrass, respectively. The remaining 33% char increase for red oak (3.1 wt% char) and 62% char increase for switchgrass (4.0 wt% char) appear to be from carbonization of sugars released during pyrolysis of acid-infused biomass.

Marjorie R. Rover, Patrick A. Johnston, Tao Jin, Ryan G. Smith, Robert C. Brown, and Laura Jarboe (2014). Production of Clean Pyrolytic Sugars for FermentationChemSusChem 7, 1662-1668.

This study explores the separate recovery of sugars and phenolic oligomers produced during fast pyrolysis with the effective removal of contaminants from the separated pyrolytic sugars to produce a substrate suitable for fermentation without hydrolysis. The first two stages from a unique recovery system capture “heavy ends”, mostly water-soluble sugars and water-insoluble phenolic oligomers. The differences in water solubility can be exploited to recover a sugar-rich aqueous phase and a phenolic-rich raffinate. Over 93 wt% of the sugars is removed in two water washes. These sugars contain contaminants such as low-molecular-weight acids, furans, and phenols that could inhibit successful fermentation. Detoxification methods were used to remove these contaminants from pyrolytic sugars. The optimal candidate is NaOH overliming, which results in maximum growth measurements with the use of ethanol-producing Escherichia coli.

Yanan Zhang, Tristan R. Brown, Guiping Hu, Robert C. Brown (2013). Techno-economic Analysis of Monosaccharide Production via Fast Pyrolysis of Lignocellulose, Bioresource Technology 127, 358-365.

The economic feasibility of a facility producing monosaccharides, hydrogen and transportation fuels via fast pyrolysis and upgrading pathway was evaluated by modeling a 2000 dry metric ton biomass/day facility using Aspen Plus®. Equipment sizing and cost were based on Aspen Economic Evaluation® software. The results indicate that monosaccharide production capacity could reach 338 metric tons/day. Co-product yields of hydrogen and gasoline were 23.4 and 141 metric tons/day, respectively. The total installed equipment and total capital costs were estimated to be $210 million and $326 million, respectively. A facility internal rate of return (IRR) of 11.4% based on market prices of $3.33/kg hydrogen, $2.92/gal gasoline and diesel, $0.64/kg monosaccharide was calculated. Sensitivity analysis demonstrates that fixed capital cost, feedstock cost, product yields, and product credits have the greatest impacts on facility IRR. Further research is needed to optimize yield of sugar via the proposed process to improve economic feasibility.

Xianglan Bai, Patrick A. Johnston, and Robert C. Brown, (2013), An Experimental Study of the Competing Processes of Evaporation and Polymerization of Levoglucosan in Cellulose Pyrolysis, Journal of Analytical and Applied Pyrolysis 99, 130-136.

While levoglucosan is a major pyrolysis product of cellulose, the yields reported in the literature vary significantly depending upon experimental conditions. In the present paper, we found that during pyrolysis in a micropyrolyzer, levoglucosan yield from cellulose can decrease significantly as sample size increases. According to our previous research, levoglucosan not only evaporates, but also forms polymers at elevated temperatures and these polymers can further dehydrate to char and low molecular weight volatiles such as water, furfural, furan, and acids. These results strongly suggest that experimental variables may influence the competing processes of evaporation and polymerization of levoglucosan during cellulose decomposition, and thereby affect the final yield of levoglucosan. In this paper, the influence of various experimental variables on the evaporation and polymerization of levoglucosan is evaluated in experiments conducted with a thermogravimetric analyzer. The pyrolytic residues are then quantified using a high performance liquid chromatography method. Experimental variables include sample size, ventilation condition, sweep gas, heating rate, and moisture content. The results show that all of the tested variables affect the competing processes of evaporation and polymerization of levoglucosan, and consequently affect the final recovery of levoglucosan.

Najeeb Kuzhiyil, Dustin Dalluge, Xianglan Bai, Kwang Ho Kim, and Robert C. Brown (2012). Pyrolytic Sugars from Cellulosic Biomass, ChemSusChem 5, 2228-2236.

Depolymerization of cellulose offers the prospect of inexpensive sugars from biomass. Breaking the glycosidic bonds of cellulose to liberate glucose has usually been pursued by acid or enzymatic hydrolysis although a purely thermal depolymerization route to sugars is also possible. Fast pyrolysis of pure cellulose yields primarily the anhydrosugar levoglucosan (LG) whereas the presence of naturally occurring alkali and alkaline earth metals (AAEMs) in biomass strongly catalyzes ring-breaking reactions that favor formation of light oxygenates. Here, we show a method of significantly increasing the yield of sugars from biomass by purely thermal means through infusion of certain mineral acids (phosphoric and sulfuric acid) into the biomass to convert the AAEMs into thermally stable salts (particularly potassium sulfates and phosphates). These salts not only passivate AAEMs that normally catalyze fragmentation of pyranose rings, but also buffer the system at pH levels that favor glycosidic bond breakage. It appears that AAEM passivation contributes to 80 % of the enhancement in LG yield while the buffering effect of the acid salts contributes to the balance of the enhancement.

Pushkaraj R. Patwardhan, Justinus A. Satrio, Robert C. Brown, Brent H. Shanks (2009). Production Distribution from Fast Pyrolysis of Glucose-based Carbohydrates, Journal of Analytical and Applied Pyrolysis 86, 323-330.


Diagram of Levogluscosan
Proposed mechanism of levoglucosan formation from polysaccharides.

Carbohydrates are the major constituents of biomass. With the growing interest in utilizing bio-oil obtained from fast pyrolysis of biomass for fuels and chemicals, understanding the carbohydrate pyrolysis behavior has gained particular importance. The chemical composition of the bio-oil is an important consideration for its upstream and/or downstream processing. Though the classification of pyrolysis products into overall tar, char and gaseous fraction has evolved as a standard; detailed knowledge of the chemical constituents that determine the quality of bio-oil has received little attention. Furthermore, the speciation arising from primary and secondary reactions has been rarely distinguished. In this study the product distribution arising from the primary reactions during 500 °C fast pyrolysis of several mono-, di- and polysaccharides is studied with the help of micro-pyrolyzer. The study suggests that levoglucosan and the low molecular weight compounds are formed through competitive pyrolysis reactions rather than sequential pyrolysis reactions. It is also shown that the orientation or the position of glycosidic linkages does not significantly influence the product distribution except with 1,6-linked polysaccharide, which showed considerably less formation of levoglucosan than other polysaccharides.