Sulfite Pretreatment To Overcome Recalcitrance Of Lignocellulose Research Articles

Exploring surface properties of substrate to understand the difference in enzymatic hydrolysis of sugarcane bagasse treated with dilute acid and sulfite

The sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) is beneficial to subsequent enzymatic hydrolysis. In this study, to elucidate enzymatic hydrolysis mechanism of SPORL treated sugarcane bagasse (SCB), the surface properties of SPORL and dilute acid (DA) treated SCBs were compared, including cellulase adsorption isotherm and kinetics, specific surface area and average size of pores, water retention value (WRV), element composition and percentages of different chemical bonds on the substrate surface. The results showed the hydrolysis yield of SPORL SCB (76.16 %) was higher than that of DA (57.82 %) and SPORL SCB had better adsorption capacity, lower binding strength, a higher cellulase adsorption rate, larger specific surface area and higher WRV, and these two SCBs might adsorb cellulase by COR bonds (R: organic groups), suggesting SPORL SCB’s surface was more advantageous to enzymatic hydrolysis. This study could help understand the mechanism of lignocellulosic hydrolysis in depth.

Effect of bisulfite treatment on composition, structure, enzymatic hydrolysis and cellulase adsorption profiles of sugarcane bagasse

The effect of sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) on composition, structure, enzymatic hydrolysis and cellulase adsorption profiles of sugarcane bagasse (SCB) was investigated. SPORL gave a higher SCB hydrolysis yield (85.33%) compared to dilute acid pretreatment (DA) (64.39%). The SEM pictures showed that SPORL SCB structure became more disordered and looser, suggesting SPORL SCB was more accessible to cellulase. The zeta potential of SPORL SCB suspension (−21.89mV) was significantly different from that of DA SCB (−12.87mV), which demonstrated the lignin in SPORL SCB was more hydrophilic. With regard to cellulase adsorption profiles, SPORL SCB had a lower non-productive adsorption (14.87mg/glignin) and a higher productive adsorption (37.67 mg/gcarbohydrate) compared with DA SCB (17.05mg/glignin; 25.79mg/gcarbohydrate). These results indicated that SPORL SCB had better accessibility to cellulase and the higher productive cellulase adsorption of SPORL SCB had improved hydrolysis.

Effects of hot water extraction (HWE) of Douglas fir as a pre-process for the sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL)

Abstract The process named “sulfite pretreatment to overcome recalcitrance of lignocellulose” (SPORL) is designed for the digestion of softwoods within the framework of the biorefinery concept. “Hot water extraction (HWE)” is an environmentally benign and low-cost pretreatment, which only needs water as a reagent. In the present study, HWE has been investigated as a pre-process prior to SPORL with Douglas fir as feedstock. The SPORL parameters, namely, temperature and treatment time, were in the range 135–155°C and 40–120 min, respectively, while the sulfuric acid concentration was 0.2–0.4% (v/v). The aim was to maximize the enzymatic digestibility of the treated wood. The severity of SPORL at different pretreatment conditions was characterized by the combined severity factor (CSF). The HWE pre-process led to a two-fold increase in specific surface area of the substrate. More hemicellulosic-derived simple sugars were dissolved in the spent liquor (SL) as the CSF increased from 1.23 to 1.82. A maximum enzymatic digestibility of 64.3% was attained when SPORL was conducted at 155°C for 120 min with a sulfuric acid concentration of 0.4% (v/v). A considerably high enzymatic digestibility (~55–60%) is still achievable by incorporating HWE prior to SPORL, even if the SPORL severity is reduced, namely to a lower temperature (145°C), a shorter time (80 min), and a lower acid volume (0.3% v/v).

Dairy Manure as a Potential Feedstock for Cost-Effective Cellulosic Bioethanol

This study investigated sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) pretreatment and subsequent enzymatic digestibility of undigested dairy manure to preliminarily assess its potential use as an inexpensive feedstock for cellulosic bioethanol production. The sulfite pretreatment was carried out in a factorial analysis using 163 to 197 °C for 3 to 37 min with 0.8% to 4.2% sulfuric acid combined with 2.6% to 9.4% sodium sulfite. These treatments were compared with other standard pretreatments of dilute acid, and hot and cold alkali pretreatments. This comparative study showed that the sulfite pretreatment, through its combined effects of hemicellulose and lignin removal and lignin sulfonation, is more effective than the diluted acid and alkali pretreatments to improve the enzymatic digestibility of dairy manure.

Molecular Structure of Sodium Lignosulfonate from Different Sources and their Properties as Dispersant of TiO2 Slurry

The molecular structure and properties of four sodium lignosulfonates (LSs) derived from pulping or bioethanol production were evaluated and compared. SXP and SAL were produced by sulfite pulping and sulfonation reaction of lignin from alkali pulping of poplar, respectively. LS-180 and LS-150 were from sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) pretreatment of lodgepole pine for bioethanol production. The molecular weights of the two LSs from SPORL were much smaller than those from pulping. However, LS-180 and LS-150 had higher sulfur content, especially LS-180. UV–Vis absorption spectra of LS-180 and SXP showed redshift, indicating increased amount of guaiacyl units or conjugated structures. The infrared spectra showed that LS-180 and SXP had more conjugated structures. LS-150 had the highest methoxyl group content, while SAL and LS-180 had lowest. The 1H-NMR was used to further investigate the difference of molecular linkages within each LS. LS-150 had more β-O-4′ structures than the others, while SXP had more β-β′ structures. When used as dispersant for TiO2 slurry, LS-180, LS-150, and SXP all had excellent dispersibility, but not SAL, suggesting LS from bioethanol production is an excellent source of LS and lignin sulfonation of alkali lignin is not sufficient for dispersion applications.

Pilot-scale demonstration of SPORL for bioconversion of lodgepole pine to bioethanol and lignosulfonate

Abstract The process sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) has been the focus of this study. Pilot-scale (50 kg) pretreatment of wood chips of lodgepole pine (Pinus contorta Douglas ex Loudon) killed by mountain pine beetle (Dendroctonus ponderosae Hopkins) were conducted at 165°C with a dilute sulfite solution of pH 2 for bioconversion to ethanol and lignosulfonate (LS). The pretreatment duration was optimized in laboratory bench scale experiments with a certain severity based on a combined hydrolysis factor (CHF). The sodium bisulfite loading was 8% and the liquor to wood ratio 3. The pretreated solids were disk milled together with the spent liquid and the resultant slurry with a 25% solids content was directly (without detoxification) submitted to a simultaneous enzymatic saccharification and fermentation (SSF) with Saccharomyces cerevisiae YRH400 at cellulase loading of 35 ml kg-1 of untreated wood. At solids loading of 20%, the alcohol yield was 288 l t-1 wood (with a final concentration of 52.2 g l-1), which corresponds to a 72.0% theoretical yield based on total glucan, mannan, and xylan. The LS from SPORL was highly sulfonated and its molecular weight was lower than that of a purified commercial softwood LS, and therefore it has a high potential as a directly marketable co-product.

Effect of Hot-Pressing Temperature on the Subsequent Enzymatic Saccharification and Fermentation Performance of SPORL Pretreated Forest Biomass

Methods to increase the energy density of biofuel feedstock for shipment are important towards improving supply chain efficiency in upstream processes. Towards this end, densified pretreated lignocellulosic biomass was produced using hot-pressing. The effects of fiber hornification induced by hot-pressing on enzymatic digestibilities of lodgepole pine and poplar NE222 wood chips pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) were examined. Pretreated wood chips were pressed at 25, 70, 90, 110, and 177 °C. The cellulose accessibilities of the pressed and unpressed substrates were evaluated using water retention value and direct cellulase adsorption measurements. Hot-pressing below 110 °C produced a degree of hornification (DH) below 0.26 and had limited effect on cellulose accessibility and enzymatic digestibility. Hot-pressing at 177 °C produced a DH of 0.86 that substantially hornified the fibers and resulted near zero saccharification. The saccharification results were consistent with cellulose accessibility data. Ethanol fermentation studies at 18 % solids suggest that a pressing below 110 °C is preferred to reduce its effect on biofuel yield.

Effects of Lignin Removal on Substrate Enzymatic Hydrolysis of SPORL-high-pH Pretreated Bagasse

The performance of a process called sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL), which was carried out at high pH, was preliminarily investigated as a means of improving bagasse substrate enzymatic digestibility (SED). The lignin removal significantly affected the SED resulting from the SPORL-high-pH treatment. Lignin removal was found to be well-correlated with SED when the Boltzmann function was used to fit the curve. In this fitting curve, SED increased slowly initially and then rose up quickly with lignin removal (from 0% to 10%, and then from 10% to 35%) and finally reached an asymptotic value (80%, based on o.d. glucan in the pretreated substrate). Removing lignin to about 35% to 40% would be sufficient to significantly improve the SED of bagasse to the asymptotic value (80%) during enzymatic hydrolysis, while low cellulase and beta-glucosidase (15 FPU/g and 22.5 CUB/g o.d. cellulose in the substrate, respectively) were loaded. Furthermore, combining this Boltzmann function and the SPORL-high-pH delignification model would be useful for predicting neutral-sulfite pretreated SED.

Lignosulfonate To Enhance Enzymatic Saccharification of Lignocelluloses: Role of Molecular Weight and Substrate Lignin

This study conducted an investigation of the effect of lignosulfonate (LS) on enzymatic saccharification of lignocelluloses. Two commercial LSs and one laboratory sulfonated kraft lignin were applied to Whatman paper, dilute acid and SPORL (sulfite pretreatment to overcome recalcitrance of lignocelluloses) pretreated aspen, and kraft alkaline and SPORL pretreated lodgepole pine. All three lignin samples inhibited cellulose saccharification of Whatman paper, but enhanced the saccharification of the four lignocellulosic substrates. The level of enhancement was related to the molecular weight and degree of sulfonation of the lignin as well as the substrate lignin structure. When different molecular weight (MW) fractions of one commercial LS (SXP), generated from sulfite pulping of hardwood, were applied to the Whatman paper, the large MW fraction (SXP1) with the lowest degree of sulfonation inhibited cellulose saccharification while the intermediate (SXP2) and smallest (SXP3) MW fractions enhanced saccharification. All MW fractions enhanced saccharification of the four lignocellulosic substrates with maximal enhancement by the smallest MW fraction, SXP3. The enhancement was most significant for the kraft lodgepole pine substrate and least significant for the SPORL pretreated lodgepole pine using all three LS and SXP fractions. The results suggest that LS acts as a surfactant to enhance pure cellullose saccharification. When LS is applied to lignocelluloses, it acts as a surfactant to block bound lignin from binding cellulase nonproductively leading to enhanced saccharification.

PH‐Induced Lignin Surface Modification to Reduce Nonspecific Cellulase Binding and Enhance Enzymatic Saccharification of Lignocelluloses

We studied the mechanism of the significant enhancement in the enzymatic saccharification of lignocelluloses at an elevated pH of 5.5-6.0. Four lignin residues with different sulfonic acid contents were isolated from enzymatic hydrolysis of lodgepole pine pretreated by either dilute acid (DA) or sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL). The adsorption isotherms of a commercial Trichoderma reesi cellulase cocktail (CTec2) produced by these lignin residues at 50 °C were measured in the pH range of 4.5-6.0. The zeta potentials of these lignin samples were also measured. We discovered that an elevated pH significantly increased the lignin surface charge (negative), which causes lignin to become more hydrophilic and reduces its coordination affinity to cellulase and, consequently, the nonspecific binding of cellulase. The decreased nonspecific cellulase binding to lignin is also attributed to enhanced electrostatic interactions at elevated pH through the increased negative charges of cellulase enzymes with low pI. The results validate the hypothesis that the increases in enzymatic saccharification efficiencies at elevated pH for different pretreated lignocelluloses are solely the result of decreased nonspecific cellulase binding to lignin. This study contradicts the well-established concept that the optimal pH is 4.8-5.0 for enzymatic hydrolysis using Trichoderma reesi cellulose, which is widely accepted and exclusively practiced in numerous laboratories throughout the world. Because an elevated pH can be easily implemented commercially without capital cost and with minimal operating cost, this study has both scientific importance and practical significance.

Lignosulfonate and elevated pH can enhance enzymatic saccharification of lignocelluloses

BackgroundNonspecific (nonproductive) binding (adsorption) of cellulase by lignin has been identified as a key barrier to reduce cellulase loading for economical sugar and biofuel production from lignocellulosic biomass. Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL) is a relatively new process, but demonstrated robust performance for sugar and biofuel production from woody biomass especially softwoods in terms of yields and energy efficiencies. This study demonstrated the role of lignin sulfonation in enhancing enzymatic saccharification of lignocelluloses – lignosulfonate from SPORL can improve enzymatic hydrolysis of lignocelluloses, contrary to the conventional belief that lignin inhibits enzymatic hydrolysis due to nonspecific binding of cellulase.ResultsThe study found that lignosulfonate from SPORL pretreatment and from a commercial source inhibits enzymatic hydrolysis of pure cellulosic substrates at low concentrations due to nonspecific binding of cellulase. Surprisingly, the reduction in enzymatic saccharification efficiency of a lignocellulosic substrate was fully recovered as the concentrations of these two lignosulfonates increased. We hypothesize that lignosulfonate serves as a surfactant to enhance enzymatic hydrolysis at higher concentrations and that this enhancement offsets its inhibitive effect from nonspecific binding of cellulase, when lignosulfonate is applied to lignocellulosic solid substrates. Lignosulfonate can block nonspecific binding of cellulase by bound lignin on the solid substrates, in the same manner as a nonionic surfactant, to significantly enhance enzymatic saccharification. This enhancement is linearly proportional to the amount of lignosulfonate applied which is very important to practical applications. For a SPORL-pretreated lodgepole pine solid, 90% cellulose saccharification was achieved at cellulase loading of 13 FPU/g glucan with the application of its corresponding pretreatment hydrolysate coupled with increasing hydrolysis pH to above 5.5 compared with only 51% for the control run without lignosulfonate at pH 5.0. The pH-induced lignin surface modification at pH 5.5 further reduced nonspecific binding of cellulase by lignosulfonate.ConclusionsThe results reported in this study suggest significant advantages for SPORL-pretreatment in terms of reducing water usage and enzyme dosage, and simplifying process integration, i.e., it should eliminate washing of SPORL solid fraction for direct simultaneous enzymatic saccharification and combined fermentation of enzymatic and pretreatment hydrolysates (SSCombF). Elevated pH 5.5 or higher, rather than the commonly believed optimal and widely practiced pH 4.8-5.0, should be used in conducting enzymatic saccharification of lignocelluloses.

Lignosulfonate-mediated cellulase adsorption: enhanced enzymatic saccharification of lignocellulose through weakening nonproductive binding to lignin

BackgroundThermochemical pretreatment of lignocellulose is crucial to bioconversion in the fields of biorefinery and biofuels. However, the enzyme inhibitors in pretreatment hydrolysate make solid substrate washing and hydrolysate detoxification indispensable prior to enzymatic hydrolysis. Sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) is a relatively new process, but has demonstrated robust performance for sugar and biofuel production from woody biomass in terms of yield and energy efficiency. This study demonstrated the advantage of SPORL pretreatment whereby the presentation of lignosulfonate (LS) renders the hydrolysate non-inhibitory to cellulase (Cel) due to the formation of lignosulfonate-cellulase complexes (LCCs) which can mediate the Cel adsorption between lignin and cellulose, contrary to the conventional belief that pretreatment hydrolysate inhibits the enzymatic hydrolysis unless detoxified.ResultsParticular emphasis was made on the formation mechanisms and stability phase of LCCs, the electrostatic interaction between LCCs and lignin, and the redistributed Cel adsorption between lignin and cellulose. The study found that LS, the byproduct of SPORL pretreatment, behaves as a polyelectrolyte to form LCCs with Cel by associating to the oppositely charged groups of protein. Compared to Cel, the zeta potential of LCCs is more negative and adjustable by altering the molar ratio of LS to Cel, and thereby LCCs have the ability to mitigate the nonproductive binding of Cel to lignin because of the enlarged electrostatic repulsion. Experimental results showed that the benefit from the reduced nonproductive binding outweighed the detrimental effects from the inhibitors in pretreatment hydrolysate. Specifically, the glucan conversions of solid substrate from poplar and lodgepole pine were greatly elevated by 25.9% and 31.8%, respectively, with the complete addition of the corresponding hydrolysate. This contradicts the well-acknowledged concept in the fields of biofuels and biorefinery that the pretreatment hydrolysate is inhibitory to enzymes.ConclusionsThe results reported in this study also suggest significant advantages of SPORL pretreatment in terms of water consumption and process integration, that is, it should abolish the steps of solid substrate washing and pretreatment hydrolysate detoxification for direct simultaneous saccharification and combined fermentation (SSCombF) of enzymatic and pretreatment hydrolysate, thereby facilitating bioprocess consolidation. Furthermore, this study not only has practical significance to biorefinery and bioenergy, but it also provides scientific importance to the molecular design of composite enzyme-polyelectrolyte systems, such as immobilized enzymes and enzyme activators, as well as to the design of enzyme separation processes using water-soluble polyelectrolytes.

Evaluation energy efficiency of bioconversion knot rejects to ethanol in comparison to other thermochemically pretreated biomass

Rejects from sulfite pulp mill that otherwise would be disposed of by incineration were converted to ethanol by a combined physical–biological process that was comprised of physical refining and simultaneous saccharification and fermentation (SSF). The energy efficiency was evaluated with comparison to thermochemically pretreated biomass, such as those pretreated by dilute acid (DA) and sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL). It was observed that the structure deconstruction of rejects by physical refining was indispensable to effective bioconversion but more energy intensive than that of thermochemically pretreated biomass. Fortunately, the energy consumption was compensated by the reduced enzyme dosage and the elevated ethanol yield. Furthermore, adjustment of disk-plates gap led to reduction in energy consumption with negligible influence on ethanol yield. In this context, energy efficiency up to 717.7% was achieved for rejects, much higher than that of SPORL sample (283.7%) and DA sample (152.8%).

Sulfite (SPORL) pretreatment of switchgrass for enzymatic saccharification

SPORL (Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose) pretreatment was applied to switchgrass and optimized through an experimental design using Response Surface Methodology within the range of temperature (163–197°C), time (3–37min), sulfuric acid dosage (0.8–4.2% on switchgrass), and sodium sulfite dosage (0.6–7.4% on switchgrass). Performance of SPORL was compared with that of dilute acid (DA) and alkali (AL) in switchgrass pretreatment. Results indicated that SPORL pretreatment improved the digestibility of switchgrass through sufficiently removing hemicellulose, partially dissolving lignin, and reducing hydrophobicity of lignin by sulfonation. The removal of hemicellulose was more critical to substrate digestibility than the removal of lignin during SPORL pretreatment. SPORL pretreated switchgrass had better enzymatic digestibility than DA and AL pretreated ones. The SPORL pretreated switchgrass could be hydrolyzed by 83% within 48h with 15FPU (filter paper unit) cellulase and 30CBU (cellobiose unit) β-glucosidase/g cellulose.

High titer ethanol production from SPORL-pretreated lodgepole pine by simultaneous enzymatic saccharification and combined fermentation

Lodgepole wood chips were pretreated by sulfite pretreatment to overcome recalcitrance of lignocelluloses (SPORL) at 25% solids loading and 180°C for 20min with sulfuric acid and sodium bisulfite charges of 2.2 and 8wt/wt% on an oven-dry wood basis, respectively. The pretreated wood chips were disk-milled with pretreatment spent liquor and water, and the solid fraction was separated from the liquor stream. The liquor was neutralized and concentrated through vacuum evaporation. Quasi-simultaneous enzymatic saccharification of the cellulosic solids and combined fermentation with the concentrated liquor was conducted at up to 20% total solids loading. Fed-batching of the solids facilitated liquefaction and saccharification, as well as managing instantaneous inhibitor concentrations. At a commercial cellulase (CTec2) loading of only 9 FPU or 0.06mL/g untreated wood, a maximum ethanol titer of 47.4g/L was achieved, resulting in a calculated yield of 285L/tonne of wood using Saccharomyces cerevisiae YRH400 at 35°C and pH 5.5.

Effects of SPORL and Dilute Acid Pretreatment on Substrate Morphology, Cell Physical and Chemical Wall Structures, and Subsequent Enzymatic Hydrolysis of Lodgepole Pine

The effects of pretreatment by dilute acid and sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) on substrate morphology, cell wall physical and chemical structures, along with the subsequent enzymatic hydrolysis of lodgepole pine substrate were investigated. FE-SEM and TEM images of substrate structural morphological changes showed that SPORL pretreatment resulted in fiber separation, where SPORL high pH (4.2) pretreatment exhibited better fiber separation than SPORL low pH (1.9) pretreatment. Dilute acid pretreatment produced very poor fiber separation, consisting mostly of fiber bundles. The removal of almost all hemicelluloses in the dilute acid pretreated substrate did not overcome recalcitrance to achieve a high cellulose conversion when lignin removal was limited. SPORL high pH pretreatment removed more lignin but less hemicellulose, while SPORL low pH pretreatment removed about the same amount of lignin and hemicelluloses in lodgepole pine substrates when compared with dilute acid pretreatment. Substrates pretreated with either SPORL process had a much higher cellulose conversion than those produced with dilute acid pretreatment. Lignin removal in addition to removal of hemicellulose in SPORL pretreatment plays an important role in improving the cellulose hydrolysis of the substrate.

Precipitation of lignosulphonates from SPORL liquid by calcium hydroxide treatment

Precipitation of lignosulphonates from the liquor for sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) by addition of Ca(OH)2 was investigated in this work. The experiment was conducted in a reaction temperature range of 20 to 75oC for 90 minutes with Ca(OH)2 charge varying from 20 to 90 g/L and a range of liquid enrichment ratio of 1 to 5. It was found that increased Ca(OH)2 charge, duration time, reaction temperature, and liquor concentration each tended to improve lignosulphonates precipitation, but tended to hurt fermentable sugars conservation. Application of Ca(OH)2 20 g/L to SPORL liquid without enrichment at 30oC for 90 minutes could be an optimal condition. Under this condition, 25.95% of the lignosulphonates was precipitated for further utilization, while calculated amounts of 106.46% of glucose and 60.25% of xylose were conserved for further fermentation.

Ethanol production from poplar wood through enzymatic saccharification and fermentation by dilute acid and SPORL pretreatments

Dilute acid (DA) and Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL) pretreatments were directly applied to wood chips of four poplar wood samples of different genotypes (hereafter referred to as poplars; Populus tremuloides Michx. ‘native aspen collection’; Populus deltoides Bartr. ex Marsh×Populus nigra L. ‘NE222’ and ‘DN5’; P. nigra×Populus maximowiczii A. Henry ‘NM6’) to evaluate their bioconversion potential. Plant biomass recalcitrance (PBR) was defined to quantitatively determine the recalcitrance of the poplars. Using DA pretreatment, NM6 produced the lowest bioconversion efficiency with a total monomeric sugar yield of 18% theoretical and an ethanol yield of 0.07Lkg−1 of wood compared with an aspen sugar yield of 47% theoretical and an ethanol yield of 0.17Lkg−1 of wood. Similar comparisons following SPORL pretreatment were 43% versus 55% and 0.11 versus 0.20Lkg−1 of wood for NM6 and aspen, respectively. Bioconversion performance of NE222 and DN5 fell between that of aspen and NM6. While substrate lignin content and lignin removal by pretreatments did not affect substrate enzymatic digestibility, the wood lignin content was found to negatively affect xylan or hemicellulose removal using both DA and SPORL pretreatments. The ability of lignin protecting hemicellulose removal dictates PBR through affecting disk milling energy for size reduction of pretreated wood chips, substrate enzymatic digestibility. The SPORL pretreatment not only improved sugar and ethanol yields over DA for all four poplars, but also better dealt with the differences among them, suggesting better tolerance to feedstock variability.

Efficient ethanol production from beetle-killed lodgepole pine using SPORL technology and Saccharomyces cerevisiae without detoxification

This study applied Sulfite Pretreatment to Overcome Recalcitrance of Lignocelluloses (SPORL) to evaluate the potential of mountain pine beetle-killed lodgepole pine for ethanol production using conventional Saccharomyces cerevisiae without hydrolysate detoxification. The results indicate that the beetle-killed trees are more susceptible to SPORL pretreatment than live trees in addition to having enriched glucan and mannan content as reported in the literature. Ethanol yields of 200 and 250 L/metric ton wood were achieved from a live tree and a dead tree (four years after infestation) without process optimization. Ethanol yield of 220 L/metric ton of wood was obtained from a downed tree with more advanced decomposition, which is approximately 10% more than that from a corresponding live tree. Process mass and energy balance analyses suggest that net ethanol energy output (before distillation, lignin energy excluded) from the decomposing tree was approximately 3.2 GJ/metric ton wood, which is 23% more than that from a corresponding live tree. The study demonstrated the robustness of the SPORL process and the utility of beetle-killed trees for cellulosic ethanol production even after many years post mortality.

Sulfite Pretreatment (SPORL) for Robust Enzymatic Saccharification of Corn Stalks

This study demonstrates sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) for robust bioconversion of corn stalks. With only about 3% sodium bisulfite charge on corn stalks and 30 min pretreatment at temperature 180°C, SPORL can achieve near complete cellulose conversion to glucose in 48h enzymatic hydrolysis. Sulfuric acid charge has great effect on SPORL pretreatment. Enzymatic cellulose conversion of substrate increased with the increase in acid charge under the studied conditions. Bisulfite with different counter-ions can be used in the SPORL. Magnesium as counter ion was found to be more effective on enzymatic hydrolysis of substrate than sodium or ammonium.