Sulfite Pretreatment To Overcome The Recalcitrance Of Lignocelluloses Research Articles

Biorefinery lignosulfonates as a dispersant for coal water slurry

Valorization of lignin from biofuel production is the key to developing biorefinery technologies for sustainable and economic utilization of lignocellulosic biomass. Here we present isolating lignosulfonate from the spent liquors of Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL)-pretreated lodgepole pine and Douglas-fir forest residue as a dispersant for coal water slurry. The two SPORL pretreatments were conducted at a pilot scale and resulted in very high ethanol yield from the pretreated biomass. Therefore, demonstrating the commercial utility of these lignosulfonates has practical significance. The two isolated biorefinery lignosulfonates (LSs), Na-LS and Ca-LS, both had a molecular weight of approximately 9000 Da. Fundamental lignin properties such as chemical structure, functional groups were analyzed. The two LSs showed slightly better to equal performance in modifying CWS rheology than a commercial dispersant naphthalene sulfonate formaldehyde condensate (FDN), despite they were less sulfonated than FDN. The practical importance of this study is that the pilot-scale pretreatments that produced the two LSs also produced excellent bioethanol yields at high titer without detoxification and washing. This suggests SPORL pretreatment is a promising technology for economic bioconversion of under-utilized woody biomass.

Fermentative High-Titer Ethanol Production from Douglas-Fir Forest Residue Without Detoxification Using SPORL: High SO2 Loading at Low Temperature

Abstract This study evaluated high sulfur dioxide (SO2) loading in applying Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) to Douglas-fir forest residue (FS-10) for ethanol production through yeast fermentation. Three pretreatments were conducted at 140°C with a targeted total SO2 loading of 32 wt% on wood, or 80 g/L in the pretreatment liquor. Magnesium was used as the metal base with a targeted combined SO2 loading of 4.4 wt% on wood. A pretreatment duration of approximately 60 min was found sufficient to effectively remove the strong recalcitrance of FS-10 with ultra-low degradation of sugar to furans. Pretreatment mixing was performed through either a rotating digester or liquor circulation, and was found to have no significant effect on pretreatment performance. The ultra-low furan formation facilitated enzymatic saccharification and fermentation at total solids loading of 20% without detoxification. At cellulase loading of 35 mL/kg FS-10, a maximal ethanol yield of 322...

Case studies on sugar production from underutilized woody biomass using sulfite chemistry

We examined two case studies to demonstrate the advantages of sulfite chemistry for pretreating underutilized woody biomass to produce sugars through enzymatic saccharification. In the first case study, we evaluated knot rejects from a magnesium-based sulfite mill for direct enzymatic sugar production. We found that the sulfite mill rejects are an excellent feedstock for sugar production. In the second study, we presented SPORL (sulfite pretreatment to overcome the recalcitrance of lignocelluloses), a sulfite pretreatment process based on modified sulfite pulping for robust bioconversion of softwood forest residues. Sulfite pulping technology is well developed, with proven commercial scalability, and sulfite pretreatment is a strong contender for commercial adoption.

Using a combined hydrolysis factor to optimize high titer ethanol production from sulfite-pretreated poplar without detoxification

Sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) was applied to poplar NE222 chips in a range of chemical loadings, temperatures, and times. The combined hydrolysis factor (CHF) as a pretreatment severity accurately predicted xylan dissolution by SPORL. Good correlations between CHF and pretreated solids enzymatic digestibility, sugar yield, and the formations of furfural and acetic acid were obtained. Therefore, CHF was used to balance sugar yield with the formation of fermentation inhibitors for high titer ethanol production without detoxification. The results indicated that optimal sugar yield can be achieved at CHF=3.1, however, fermentation using un-detoxified whole slurries of NE222 pretreated at different severities by SPORL indicated CHF≈2 produced best results. An ethanol titer of 41g/L was achieved at total solids of approximately 20wt% without detoxification with a low cellulase loading of 15FPU/g glucan (27mL/kg untreated wood).

High titer and yield ethanol production from undetoxified whole slurry of Douglas-fir forest residue using pH profiling in SPORL.

BackgroundForest residue is one of the most cost-effective feedstock for biofuel production. It has relatively high bulk density and can be harvested year round, advantageous for reducing transportation cost and eliminating onsite storage. However, forest residues, especially those from softwood species, are highly recalcitrant to biochemical conversion. A severe pretreatment for removing this recalcitrance can result in increased sugar degradation to inhibitors and hence cause difficulties in fermentation at high solid loadings. Here, we presented high titer ethanol production from Douglas-fir forest residue without detoxification. The strong recalcitrance of the Douglas-fir residue was removed by sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL). Sugar degradation to inhibitors was substantially reduced using a novel approach of “pH profiling” by delaying acid application in pretreatment, which facilitated the simultaneous enzymatic saccharification and fermentation of undetoxified whole slurry at a solid loading of 21%.Results“pH profiling” reduced furan production by approximately 70% in using SPORL pretreating Douglas-fir forest residue (FS-10) comparing with the control run while without sacrificing enzymatic saccharification of the resultant substrate. pH profiling also reduced carbohydrate degradation. The improved carbohydrate yield in pretreated solids and reduced fermentation inhibitors with pH profiling resulted in a terminal ethanol titer of 48.9 ± 1.4 g/L and yield of 297 ± 9 L/tonne FS-10, which are substantially higher, i.e., by 27% in titer and by 38% in yield, than those of a control SPORL run without pH profiling.ConclusionsEconomical and large-volume production of commodity biofuels requires the utilization of feedstocks with low value (therefore low cost) and sustainably producible in large quantities, such as forest residues. However, most existing pretreatment technologies cannot remove the strong recalcitrance of forest residues to produce practically fermentable high titer sugars. Here, we demonstrated a commercially scalable and efficient technology capable of removing the strong recalcitrant nature of forest residues using “pH profiling” together with “low temperature SPORL”. The resultant pretreated whole slurry of a Douglas-fir forest residue using this technology can be easily processed at high solids of 21% without detoxification to achieve a high ethanol yield of 297 L/tonne at 48.9 g/L.Graphical Graphic table of content.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0205-3) contains supplementary material, which is available to authorized users.

Using sulfite chemistry for robust bioconversion of Douglas-fir forest residue to bioethanol at high titer and lignosulfonate: A pilot-scale evaluation

This study demonstrated at the pilot-scale (50kg) use of Douglas-fir forest harvest residue, an underutilized forest biomass, for the production of high titer and high yield bioethanol using sulfite chemistry without solid–liquor separation and detoxification. Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) was directly applied to the ground forest harvest residue with no further mechanical size reduction, at a low temperature of 145°C and calcium bisulfite or total SO2 loadings of only 6.5 or 6.6wt% on oven dry forest residue, respectively. The low temperature pretreatment facilitated high solids fermentation of the un-detoxified pretreated whole slurry. An ethanol yield of 282L/tonne, equivalent to 70% theoretical, with a titer of 42g/L was achieved. SPORL solubilized approximately 45% of the wood lignin as directly marketable lignosulfonate with properties equivalent to or better than a commercial lignosulfonate, important to improve the economics of biofuel production.

Comparisons of five Saccharomyces cerevisiae strains for ethanol production from SPORL-pretreated lodgepole pine.

The performances of five yeast strains under three levels of toxicity were evaluated using hydrolysates from lodgepole pine pretreated by Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL). The highest level of toxicity was represented by the whole pretreated biomass slurry, while intermediate toxicity was represented by the hydrolysate with partial loading of pretreatment spent liquor. The zero toxicity was represented using the enzymatic hydrolysate produced from thoroughly washed SPORL lodgepole pine solids. The results indicate that strains D5A and YRH400 can tolerate the whole pretreated biomass slurry to produce 90.1 and 73.5% theoretical ethanol yield. Strains Y1528, YRH403, and FPL450 did not grow in whole hydrolysate cultures and were observed to have lower ethanol productivities than D5A and YRH400 on the hydrolysate with intermediate toxicity. Both YRH400 and YRH403 were genetically engineered for xylose fermentation but were not able to consume xylose efficiently in hydrolysate.

Ethanol production from non-detoxified whole slurry of sulfite-pretreated empty fruit bunches at a low cellulase loading.

Sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) was applied to an empty fruit bunches (EFB) for ethanol production. SPORL facilitated delignification through lignin sulfonation and dissolution of xylan to result in a highly digestible substrate. The pretreated whole slurry was enzymatically saccharified at a solids loading of 18% using a relatively low cellulase loading of 15 FPU/g glucan and simultaneously fermented without detoxification using Saccharomyces cerevisiae of YRH400. An ethanol yield of 217 L/tonne EFB was achieved at titer of 32 g/L. Compared with literature studies, SPORL produced high ethanol yield and titer with much lower cellulase loading without detoxification.

Using low temperature to balance enzymatic saccharification and furan formation during SPORL pretreatment of Douglas-fir

Comparing analytical results for Sulfite Pretreatment to Overcome the Recalcitrance of Lignocelluloses (SPORL) of Douglas-fir (Pseudotsuga menziesii) at two different temperatures shows that the apparent activation energy of sugar degradation is higher than that of hemicellulose hydrolysis, approximately 161kJ/mole versus 100kJ/mole. Thus, one can balance the production of degradation products against hemicellulose hydrolysis and therefore the enzymatic saccharification efficiency of the resultant substrate by changing pretreatment temperature and duration. Specifically, pretreatment at 165°C for 75min significantly reduced furan formation compared with the pretreatment at 180°C for 30min while maintaining the same pretreatment severity and therefore the same substrate enzymatic digestibility (SED). Obtaining high SED with Douglas-fir is also limited by lignin content. Fortunately, the bisulfite in SPORL provides delignification activity. By combining kinetic models for hemicelluloses hydrolysis, sugar degradation, and delignification, the performance of pretreatment can be optimized with respect to temperature, duration, acid, and bisulfite loading. The kinetic approach taken in this study is effective to design viable low temperature pretreatment processes for effective bioconversion of lignocelluloses.

Comparison of Dilute Acid and Sulfite Pretreatment for Enzymatic Saccharification of Earlywood and Latewood of Douglas fir

This study applied dilute acid (DA) and sulfite pretreatment to overcome the recalcitrance of lignocelluloses (SPORL) to deconstruct earlywood and latewood cell walls of Douglas fir for fermentable sugars production through subsequent enzymatic hydrolysis. DA pretreatment removed almost all the hemicelluloses, while SPORL at initial pH = 4.5 (SP-B) removed significant amount of lignin between 20 and 25 %. But both are not sufficient for effective enzymatic saccharification. SPORL at low initial pH = 2 (SP-AB) combines the advantage of both DA and SPORL-B to achieve approximately 90 % hemicellulose removal and delignification of 10–20 %. As a result, SP-AB effectively removed recalcitrance and thereby significantly improved enzymatic saccharification compared with DA and SP-B. Results also showed that earlywood with significantly lower density produced less saccharification after DA pretreatment, suggesting that wood density does not contribute to recalcitrance. The thick cell wall of latewood did not limit chemical penetration in pretreatments. The high lignin content of earlywood limited the effectiveness of DA pretreatment for enzymatic saccharification, while hemicellulose limits the effectiveness of high pH pretreatment of SP-B. The higher hemicellulose content in the earlywood and latewood of heartwood reduced saccharification relative to the corresponding earlywood and latewood in the sapwood using DA and SP-AB.