Philipp M. Grande

From biomass to feedstock: one-step fractionation of lignocellulose components by the selective organic acid-catalyzed depolymerization of hemicellulose in a biphasic system

A concept for a highly integrated fractionation of lignocellulose in its main components (cellulose-pulp, soluble hemicellulose sugars and lignin) is described, based on the selective catalytic depolymerization of hemicellulose in a biphasic solvent system. This leads to an effective disentanglement of the compact lignocellulose structure, liberating and separating the main components in a single step. At mild temperatures (80–140 °C), oxalic acid catalyzes selectively the depolymerization of hemicellulose to soluble sugars in aqueous solution, whereas the more crystalline cellulose-pulp remains solid and inaccessible to the acid catalysis. In the presence of a second organic phase consisting of bio-based 2-methyltetrahydrofuran (2-MTHF), lignin is directly separated from the pulp and the soluble carbohydrates by in situextraction. The oxalic acid catalyst can be crystallized from the aqueous solution, recovered and re-used. The delignified cellulose-pulp obtained from this biphasic system can be directly subjected to enzymatic depolymerization, affording soluble oligomers and glucose at rates almost comparable to those observed for the hydrolysis of commercial microcrystalline Avicel®. Overall, the concept may offer a promising approach for an efficient and selective pre-treatment of lignocellulosic materials under mild and environmentally-friendly conditions.

Iron-Catalyzed Furfural Production in Biobased Biphasic Systems: From Pure Sugars to Direct Use of Crude Xylose Effluents as Feedstock

Selective catalytic routes for processing the carbohydrate fractions of lignocellulose to deliver valuable platform chemicals are important and challenging paths for biomass valorization. A key step in this value chain is the dehydration of monomeric sugars to afford furan derivatives as valuable materials for numerous applications. Furfural can be derived from the C5sugar xylose, which is the most abundant sugar of the hemicellulose fraction in lignocellulose. Chemical approaches for xylose dehydration usually involve acidic conditions, using either mineral acids 5, 8] or acidic heterogeneous catalysts such as zeolites, MCM-41 materials, and heteropolyacids. To overcome humin formation in furfural dehydration, 13] the application of aqueous biphasic systems (using organic solvents such as methyl isobutyl ketone or toluene) for the in situ extraction of furfural has recently been proposed. 14–16] For sugar dehydration, different catalysts (e.g. , CrCl2, ZnCl2, FeCl3) have been assessed in non-aqueous deep-eutectic solvents such as choline chloride fructose mixtures as well as in monophasic aqueous media. 19] In this Communication a biphasic approach for xylose dehydration to afford furfural is reported. The approach is based on aqueous solutions of FeCl3·6 H2O and NaCl, combined with a second 2-methyltetrahydrofuran (2-MTHF) phase as biomass-derived solvent (Figure 1). After proof-of-concept experiments using pure commercially available crystalline xylose, the dehydration strategy is also assessed by directly using the aqueous, nonpurified xylose effluent obtained from pretreatment of lignocellulose with oxalic acid. In preliminary experiments, aqueous solutions of xylose were treated with catalytic amounts of different catalysts [i.e. , Fe(acac)3, FeCl3·6 H2O, FeSO4·7 H2O, FeCl2·4 H2O, MnCl2, Cu(OAc)2, and CuCl2·2 H2O] and subsequently layered with 2MTHF as organic phase. Among the tested catalysts, FeCl3·6 H2O displayed superior results and hence was selected for further assessments. After conducting the reaction at 140 8C for up to 6 h, the resulting furfural concentration in the 2-MTHF phase was determined by gas chromatography (GC). Initial kinetic measurements were taken with FeCl3·6 H2O loadings of 40 mol %. The furfural yield increased linearly up to 40 % furfural yield after 6 h. Hence the furfural production rate kfurfural was determined, based on the slope of the data from kinetic experiments conducted on 1 mmol scale. Further studies were done to optimize the efficiency. Thus, different amounts of NaCl were added to the aqueous phase (Table 1). The furfural production rate kfurfural improved considerably with increasing NaCl loading (Table 1, entries 1, 3–6). The rate could be increased by a factor of more than two by adding 20 wt % NaCl (entries 1 and 5). The effect of salt has been suggested to enhance the partitioning coefficient of furfural to organic phase. Consequently, running the reaction with 20 wt % NaCl (entry 5) for 4 h afforded a 70 % yield of furfural. However, the yield did not increase at longer reaction times (6 h) due to humin formation, which was avoided by applying shorter residence times. Increasing the amount of catalyst (up to 0.6 mmol) at 20 wt % NaCl loading afforded high furfural yields, of 65 to 70 %, after 2 h reaction time at 140 8C. A further increase of the NaCl loading to 30 wt % did not result in a better furfural production rate (entry 6), presumably due to furfural degradation. Finally, previous studies on biomass processing showed the potential of using seawater as solvent. 23] Gratifyingly, in this case the direct use of seawater (comprising different salts) with FeCl3·6 H2O also resulted in an improved furfural production rate (entry 8). Aqueous solutions of FeCl3 (0.08 m) are acidic (pH 1.4). To assess whether or not the sugar dehydration in these solutions was dominated by Brønsted acidity, we ran control experiments in aqueous HCl with an identical proton concentration, c(H) = 0.04 m. Table 1, entries 1 and 2 show that the dehydration rate with FeCl3·6 H2O is significantly higher than that with HCl at the same pH. Consistently, the addition of NaCl improves the performance of both, HCl and FeCl3·6 H2O, but with largely superior outcomes in the case of FeCl3·6 H2O (entries 6 and 7). This demonstrates that the activity of FeCl3·6 H2O in xylose dehydration is not solely governed by its Brønsted acidity. Figure 1. Iron-catalyzed xylose dehydration. 98 % of the furfural was extracted into the 2-MTHF phase.

Biomass pretreatment affects Ustilago maydis in producing itaconic acid

BackgroundIn the last years, the biotechnological production of platform chemicals for fuel components has become a major focus of interest. Although ligno-cellulosic material is considered as suitable feedstock, the almost inevitable pretreatment of this recalcitrant material may interfere with the subsequent fermentation steps. In this study, the fungus Ustilago maydis was used to produce itaconic acid as platform chemical for the synthesis of potential biofuels such as 3-methyltetrahydrofuran. No studies, however, have investigated how pretreatment of ligno-cellulosic biomass precisely influences the subsequent fermentation by U. maydis. Thus, this current study aims to first characterize U. maydis in shake flasks and then to evaluate the influence of three exemplary pretreatment methods on the cultivation and itaconic acid production of this fungus. Cellulose enzymatically hydrolysed in seawater and salt-assisted organic-acid catalysed cellulose were investigated as substrates. Lastly, hydrolysed hemicellulose from fractionated beech wood was applied as substrate.ResultsU. maydis was characterized on shake flask level regarding its itaconic acid production on glucose. Nitrogen limitation was shown to be a crucial condition for the production of itaconic acid. For itaconic acid concentrations above 25 g/L, a significant product inhibition was observed. Performing experiments that simulated influences of possible pretreatment methods, U. maydis was only slightly affected by high osmolarities up to 3.5 osmol/L as well as of 0.1 M oxalic acid. The production of itaconic acid was achieved on pretreated cellulose in seawater and on the hydrolysed hemicellulosic fraction of pretreated beech wood.ConclusionThe fungus U. maydis is a promising producer of itaconic acid, since it grows as single cells (yeast-like) in submerged cultivations and it is extremely robust in high osmotic media and real seawater. Moreover, U. maydis can grow on the hemicellulosic fraction of pretreated beech wood. Thereby, this fungus combines important advantages of yeasts and filamentous fungi. Nevertheless, the biomass pretreatment does indeed affect the subsequent itaconic acid production. Although U. maydis is insusceptible to most possible impurities from pretreatment, high amounts of salts or residues of organic acids can slow microbial growth and decrease the production. Consequently, the pretreatment step needs to fit the prerequisites defined by the actual microorganisms applied for fermentation.

Fractionation of lignocellulosic biomass using the OrganoCat process

The fractionation of lignocellulose in its three main components, hemicellulose, lignin and cellulose pulp can be achieved in a biphasic system comprising water and bio-based 2-methyltetrahydrofuran (2-MeTHF) as solvents and oxalic acid as catalyst at mild temperatures (up to 140 °C). This so-called OrganoCat concept relies on selective hemicellulose depolymerization to form an aqueous stream of the corresponding carbohydrates, whereas solid cellulose pulp remains suspended and the disentangled lignin is to a large extent extracted in situ with the organic phase. In the present paper, it is demonstrated that biomass loadings of 100 g L−1 can be efficiently fractionated within 3 h whereby the mild conditions assure that no significant amounts of by-products (e.g. furans) are formed. Removing the solid pulp by filtration allows to re-use the water and organic phase without product separation in repetitive batch mode. In this way, (at least) 400 g L−1 biomass can be processed in 4 cycles, leading to greatly improved biomass-to-catalyst and biomass-to-solvent ratios. Economic analysis of the process reveals that the improved biomass loading significantly reduces capital and energy costs in the solvent recycle, indicating the importance of process integration for potential implementation. The procedure was successfully scaled-up from the screening on bench scale to 3 L reactor. The feedstock flexibility was assessed for biomasses containing moderate-to-high hemicellulose content.

Chemo‐Enzymatic Conversion of Glucose into 5‐Hydroxymethylfurfural in Seawater

Do you sea water? Water consumption will be a challenge in biorefineries, and the use of non-drinkable sources of water will be preferred. Herein, glucose is converted into 5-hydroxymethylfurfural (HMF) in a chemo-enzymatic one-pot, two-step procedure, involving immobilized glucose isomerase to produce fructose and oxalic acid to dehydrate it to HMF.

Liquid/liquid extraction of biomass-derived lignin from lignocellulosic pretreatments

Despite the rapid progress in the field of biomass fractionation and lignin valorization, no industrial process for chemical utilization of lignin has yet been established. One major step in that direction has been made with the advent of biorefineries and new biomass fractionation methods that deliver a relatively clean lignin stream, allowing a more efficient recovery and utilization of this fraction. However, the transfer of lignin from the fractionation solvent to a different medium for subsequent valorization has been largely disregarded so far. In this work, we demonstrate the use of a green liquid/liquid-extraction to transfer lignin from the organic phase of the OrganoCat process into differently concentrated alkaline solutions for further utilization. We show that alkaline solutions of pH 13 and 14 are able to almost completely extract the OrganoCat lignin from the organic phase but that this extraction might be accompanied by changes in the molecular structure of lignin, here shown by a change in the apparent molecular weight distribution.

Multi-step biocatalytic depolymerization of lignin

Lignin is a biomass-derived aromatic polymer that has been identified as a potential renewable source of aromatic chemicals and other valuable compounds. The valorization of lignin, however, represents a great challenge due to its high inherent functionalization, what compromises the identification of chemical routes for its selective depolymerization. In this work, an in vitro biocatalytic depolymerization process is presented, that was applied to lignin samples obtained from beech wood through OrganoCat pretreatment, resulting in a mixture of lignin-derived aromatic monomers. The reported biocracking route comprises first a laccase-mediator system to specifically oxidize the Cα hydroxyl group in the β-O-4 structure of lignin. Subsequently, selective β-O-4 ether cleavage of the oxidized β-O-4 linkages is achieved with β-etherases and a glutathione lyase. The combined enzymatic approach yielded an oily fraction of low-molecular-mass aromatic compounds, comprising coniferylaldehyde and other guaiacyl and syringyl units, as well as some larger (soluble) fractions. Upon further optimization, the reported biocatalytic route may open a valuable approach for lignin processing and valorization under mild reaction conditions.

Insights into cell wall structure of Sida hermaphrodita and its influence on recalcitrance

The perennial plant Sida hermaphrodita (Sida) is attracting attention as potential energy crop. Here, the first detailed view on non-cellulosic Sida cell wall polysaccharide composition, structure and architecture is given. Cell walls were prepared from Sida stems and sequentially extracted with aqueous buffers and alkali. The structures of the quantitatively predominant polysaccharides present in each fraction were determined by biochemical characterization, glycome profiling and mass spectrometry. The amounts of glucose released by Accellerase-1500® treatment of the cell wall and the cell wall residue remaining after each extraction were used to assess the roles of pectin and hemicellulose in the recalcitrance of Sida biomass. 4-O-Methyl glucuronoxylan with a low proportion of side substitutions was identified as the major non-cellulosic glycan component of Sida stem cell walls. Pectic polysaccharides and xylans were found to be associated with lignin, suggesting that these polysaccharides have roles in Sida cell wall recalcitrance to enzymatic hydrolysis.

OrganoCat pretreatment of perennial plants: Synergies between a biogenic fractionation and valuable feedstocks

A successful biorefinery needs to align suitable pretreatment with sustainable production of biomasses. Herein, four perennial plants, (Sida, Silphium, Miscanthus and Szarvasi) regarded as promising feedstocks for biorefineries were subjected to the OrganoCat pretreatment. The technology was successfully applied to the different perennial plants revealing that pretreatment of grasses was more efficient than of non-grasses. Thorough analyses of the lignocellulose - before and after fractionation - enabled a detailed description of the fate of cellulosic, non-cellulosic polysaccharides and lignin during the pretreatment. Especially Szarvasi pulp displayed outstanding results in terms of fractionation efficiency and enzymatic digestibility, though in all cases successful lignocellulose fractionation was observed. These insights into the structural composition of different perennial plant species and the impact of the OrganoCat pretreatment on the plant material leads to useful information to strategically adapt such processes to the individual lignocellulosic material aiming for a full valorisation.

From beech wood to itaconic acid: case study on biorefinery process integration

Renewable raw materials in sustainable biorefinery processes pose new challenges to the manufacturing routes of platform chemicals. Beside the investigations of individual unit operations, the research on process chains, leading from plant biomass to the final products like lactic acid, succinic acid, and itaconic acid is increasing. This article presents a complete process chain from wooden biomass to the platform chemical itaconic acid. The process starts with the mechanical pretreatment of beech wood, which subsequently is subjected to chemo-catalytic biomass fractionation (OrganoCat) into three phases, which comprise cellulose pulp, aqueous hydrolyzed hemicellulose, and organic lignin solutions. Lignin is transferred to further chemical valorization. The aqueous phase containing oxalic acid as well as hemi-cellulosic sugars is treated by nanofiltration to recycle the acid catalyst back to the chemo-catalytic pretreatment and to concentrate the sugar hydrolysate. In a parallel step, the cellulose pulp is enzymatically hydrolyzed to yield glucose, which—together with the pentose-rich stream—can be used as a carbon source in the fermentation. The fermentation of the sugar fraction into itaconic acid can either be performed with the established fungi Aspergillus terreus or with Ustilago maydis. Both fermentation concepts were realized and evaluated. For purification, (in situ) filtration, (in situ) extraction, and crystallization were investigated. The presented comprehensive examination and discussion of the itaconate synthesis process—as a case study—demonstrates the impact of realistic process conditions on product yield, choice of whole cell catalyst, chemocatalysts and organic solvent system, operation mode, and, finally, the selection of a downstream concept.