Ionic Liquid Pretreatment Research Articles

Demonstrating a separation-free process coupling ionic liquid pretreatment, saccharification, and fermentation withRhodosporidium toruloidesto produce advanced biofuels

A lignocellulose to bisabolene bioconversion process is demonstrated to be fully compatible with [Ch][Lys].

Ionic Liquid Pretreatment of Lignocellulosic Biomass for Enhanced Enzymatic Delignification.

Ionic liquids (ILs), a potentially attractive "green," recyclable alternative to environmentally harmful volatile organic compounds, have been increasingly exploited as solvents and/or cosolvents and/or reagents in a wide range of applications, including pretreatment of lignocellulosic biomass for further processing. The enzymatic delignification of biomass to degrade lignin, a complex aromatic polymer, has received much attention as an environmentally friendly process for clean separation of biopolymers including cellulose and lignin. For this purpose, enzymes are generally isolated from naturally occurring fungi or genetically engineered fungi and used in an aqueous medium. However, enzymatic delignification has been found to be very slow in these conditions, sometimes taking several months for completion. In this chapter, we highlight an environmentally friendly and efficient approach for enzymatic delignification of lignocellulosic biomass using room temperature ionic liquids (ILs) as (co)solvents or/and pretreatment agents. The method comprises pretreatment of lignocellulosic biomass in IL-aqueous systems before enzymatic delignification, with the aim of overcoming the low delignification efficiency associated with low enzyme accessibility to the solid substrate and low substrate and product solubilities in aqueous systems. We believe the processes described here can play an important role in the conversion of lignocellulosic biomass-the most abundant renewable biomaterial in the world-to biomaterials, biopolymers, biofuels, bioplastics, and hydrocarbons. Graphical Abstract.

Analysis of an Ionic Liquid and Salt Tolerant Microbial Consortium Which Is Useful for Enhancement of Enzymatic Hydrolysis and Biogas Production

Production of biofuels and biochemicals from lignocellulosic biomass via biorefining process requires both efficient pretreatment and cellulase enzymes to improve saccharification. Ionic liquid (IL) pretreatment is one of the competent methods to modify recalcitrant structures of lignocellulosic biomass, however, IL inhibits cellular metabolisms and cellulase activities. In this study, a lignocellulose degrading microbial consortium, named CT-1, was newly bred from saline soil sample by successive subcultivations and was cultured to produce IL-tolerant cellulase enzymes. The CT-1 showed high degradation activity on various cellulosic substrates, including rice straw, corn stover, and mixed vegetable residues. In the presence of 1 M of an IL, 1-ethyl-3-methylimidazolium acetate (EMIM-Ac), activity of cellulase produced from CT-1 remained more than 95% of non-IL condition. For application in biogas production, the CT-1 was mixed with activated wastewater sludge and rice straw residues in batch anaerobic digester. Addition of CT-1 enhanced biogas production for 6.5 times (170.92 mL/g-VS) compared to the control batch. The bacterial population distribution of CT-1 was analyzed by quantitative PCR with specific primers and the results showed that Bacteroidetes, Actinobacteria and Methanosarcinales were major members that corresponding with the activities of biomass degradation and biogas production. Overall, these results demonstrated the potential of CT-1 in biorefining process of lignocellulosic biomass with compatibility to IL pretreatment.

Coal structure change by ionic liquid pretreatment for enhancement of fixed-bed gasification with steam and CO2

An innovative pretreatment of Indonesian low-rank coal (ILRC) by 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) ionic liquid (IL) was conducted. The obtained IL pretreated coal had a loose and porous structure. Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) analysis showed that pretreated ILRC had a stronger absorption ability and an increased average pore size (from 23.6 to 51.8 nm). Steam-coal gasification was conducted to explore the effect of coal pretreatment. The result showed that 1.63-times more hydrogen was generated from pretreated coal compared to original (i.e., untreated) coal, and carbon conversion (X c ) increased from 89.03 to 97.25%. During CO2 coal gasification, IL pretreated coal had a greater CO2 consumption potential and generated more CO. The chemical exergy of syngas of the pretreated coal gasification was higher than that of the untreated coal gasification with CO2 at 900 °C. In addition, pretreated coal emitted less CO2 than untreated coal at 900 °C.

Recycled ionic liquid 1-ethyl-3-methylimidazolium acetate pretreatment for enhancing enzymatic saccharification of softwood without cellulose regeneration

In this work, pretreatment of wood meals using a recycled ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), enhanced glucose liberation by enzymatic saccharification, without dissolution of cellulose and lignin. In contrast, previous studies on IL pretreatment have mostly focused on lignocellulosic dissolution to regenerate cellulose and removing lignin. Softwood (Cryptomeria japonica) was pretreated with [Emim]Ac at 60–100 °C for 2–8 h without collecting regenerated cellulose. The pretreatment did not have a strong effect on wood component dissolution (weight of residues: 91.7–98.8%). The residues contained relatively high amounts of lignin (26.6–32.6%) with low adsorption of [Emim]Ac (0.9–2.7%). Meanwhile, the crystallinity index (C r I) of cellulose in the wood was significantly reduced by pretreatment, from 50.9% to 28.4–37.1%. In spite of the high lignin contents in the residues, their glucose liberation values by enzymatic saccharification using a cellulase mixture were 3–16 times greater than that of untreated wood. A good correlation was found between the saccharification effectiveness of pretreated samples and the C r I. Although lignin dissolved in [Emim]Ac continued to accumulate after repeated use of [Emim]Ac, the pretreatment was found to be effective for three consecutive cycles without the need to remove the dissolved materials.

Nanoscale Observation of Microfibril Swelling and Dissolution in Ionic Liquids

Ionic liquids (ILs) are widely used for biomass pretreatment because of their excellent dissolving capacity. The efficient and economical use of ILs in pretreatment greatly depends on revealing the underlying mechanism of biomass dissolution. Here, we observed that cellulose microfibrils of rice straw swelled in ILs using atomic force microscopy, and the swelling resulted in a decrease in cellulose crystallinity as determined by time-course X-ray diffraction analysis. The swelling of the IL-induced cellulose microfibrils greatly promoted the saccharification efficiency of rice straw. Compared with conventional acid or alkali solutions, strong hydrogen bond interactions between ILs of the appropriate size and polysaccharides resulted in cellulose microfibrils swelling in ILs, which was demonstrated by nuclear magnetic resonance and molecular simulation. Therefore, microfibril swelling is the key step in cellulose dissolution with ILs; effective swelling could accelerate cellulose dissolution and biomass pr...

Optimizing treatment condition of coir fiber with ionic liquid and subsequent enzymatic hydrolysis for future bioethanol production

In the present study, we pretreated coir fiber with an ionic liquid (IL), n-butylammonium acetate, to expose its cellulose fibers. The best IL pretreatment conditions were determined by central composite design using a desirability function to maximize the enzymatic hydrolysis. To collect data for this optimization, coir fiber was subjected to a pulping process with 9% (w/w) sodium hydroxide for 6 h at 137 °C with a pressure of 2.5 atm. The pulping fiber was then treated with the IL for a range of times and at a range of temperatures. Based on the results, the best treatment conditions were determined to be 90 °C for 40 h. The best conditions for enzymatic hydrolysis were determined to be pH 6 at 44.16 °C for 25.57 h. Under these conditions, 32.33 ± 1.08% of the coir fiber was converted to glucose. The efficiency obtained with pulped coir fiber was 14.34 ± 0.14% and with crude coir fiber was 6.27 ± 0.15%, demonstrating the benefits of the proposed IL pretreatment.

Oxidative depolymerization potential of biorefinery lignin obtained by ionic liquid pretreatment and subsequent enzymatic saccharification of eucalyptus

This study compared the oxidative depolymerization potential between ionic liquid (IL)-pretreated/enzyme lignin, diluted acid (DA)-pretreated/enzyme lignin, and soda lignin of eucalyptus, by means of alkaline nitrobenzene or cupric oxide (CuO) oxidation which depolymerize lignin into phenolic aldehydes such as vanillin and syringaldehyde. Here, the IL-pretreated/enzyme lignin was prepared by 1-ethyl-3-methylimidazolium acetate pretreatment and subsequent enzymatic saccharification. Upon the oxidative depolymerization of lignin sample by alkaline nitrobenzene oxidation, total yield of vanillin and syringaldehyde was 36.6% for untreated control eucalyptus. In contrast, the yield was enhanced upto 48.0% for IL-pretreated/enzyme lignin. As for the soda lignin prepared by alkali cooking, the yield was 29.0%. As for the DA-pretreated/enzyme lignin prepared by DA pretreatment and subsequent enzymatic saccharification, the yield was 39.5%. Therefore, it was found that the IL-pretreated/enzyme lignin showed the highest yield of phenolic aldehydes (vanillin and syringaldehyde) via alkaline oxidation, namely, highest oxidative depolymerization potential among the lignin tested.

Lignocellulose nanofibers prepared by ionic liquid pretreatment and subsequent mechanical nanofibrillation of bagasse powder: Application to esterified bagasse/polypropylene composites

In the present study, we examined the efficacy of choline acetate (ChOAc, a cholinium ionic liquid))-assisted pretreatment of bagasse powder for subsequent mechanical nanofibrillation to produce lignocellulose nanofibers. Bagasse sample with ChOAc pretreatment and subsequent nanofibrillation (ChOAc/NF-bagasse) was prepared and compared to untreated control bagasse sample (control bagasse), bagasse sample with nanofibrillation only (NF-bagasse) and with ChOAc pretreatment only (ChOAc-bagasse). The specific surface area was 0.83m2/g, 3.1m2/g, 6.3m2/g, and 32m2/g for the control bagasse, ChOAc-bagasse, NF-bagasse, and the ChOAc/NF-bagasse, respectively. Esterified bagasse/polypropylene composites were prepared using the bagasse samples. ChOAc/NF-bagasse exhibited the best dispersion in the composites. The tensile toughness of the composites was 0.52J/cm3, 0.73J/cm3, 0.92J/cm3, and 1.29J/cm3 for the composites prepared using control bagasse, ChOAc-bagasse, NF-bagasse, and ChOAc/NF-bagasse, respectively. Therefore, ChOAc pretreatment and subsequent nanofibrillation of bagasse powder resulted in enhanced tensile toughness of esterified bagasse/polypropylene composites.

Characterization of ionic liquid pretreated plant cell wall for improved enzymatic digestibility

An insight into the properties of cell wall of mustard stalk (MS) pretreated by five ionic liquids (ILs) revealed ILs interaction with cellulose, hemicellulose and lignin components. Differential Scanning Calorimetry (DSC) showed increased pore size coupled with increased population of pores evoked by certain ILs in better facilitating enzymatic accessibility. Interestingly, all the five ILs predominantly increased the propensity of two pore sizes formation; 19 and 198 nm, but remarkable difference in the pore volumes of pretreated MS suggested the supremacy of [OAc]− based ILs, resulting in higher glucose yields. Cellulose I to II transition in pretreated MS was supported by the reduced total crystallinity index (TCI), lateral order index (LOI) values. Strong inverse correlation existed between the said parameters and residual acetyl content with enzymatic hydrolysis (R2 > 0.8). An inverse relationship between hydrogen bond basicity, LOI and TCI suggested it to be a good indicator of IL pretreatment efficiency.

Life-Cycle Greenhouse Gas and Water Intensity of Cellulosic Biofuel Production Using Cholinium Lysinate Ionic Liquid Pretreatment

Cellulosic biofuels present an opportunity to meet a significant fraction of liquid transportation fuel demand with renewable, low-carbon alternatives. Certain ionic liquids (ILs) have proven effective at facilitating hydrolysis of lignocellulose to produce fermentable sugars with high yields. Although their negligible vapor pressure and low flammability make ILs attractive solvents at the point of use, their life-cycle environmental impacts have not been investigated in the context of cellulosic biorefineries. This study provides the first life-cycle greenhouse gas (GHG) and water use inventory for biofuels produced using IL pretreatment. We explore two corn stover-to-ethanol process configurations: the conventional water-wash (WW) route and the more recently developed integrated high gravity (iHG) route, which eliminates washing steps after pretreatment. Our results are based on the use of a representative IL, cholinium lysinate ([Ch][Lys]). We find that the WW process results in unacceptably high GHG e...

The effect of ionic liquids pretreatment on the distribution and structure of alkali-soluble hemicelluloses from Eucalyptus

Abstract In this study, Eucalyptus was treated by an integrated process based on ionic liquids ([Bmim]Cl and [Bmim]OAc) combined with successive alkali solutions (0.5, 2.0, and 4.0% NaOH). The dynamic distribution changes of hemicelluloses on the morphologically distinct regions in the treated Eucalyptus cell walls revealed that the dissolution of hemicelluloses mainly occurred in the secondary layers during this process. In addition, the structural features of alkali-soluble hemicelluloses dissolved from ionic liquids pretreated Eucalyptus were thoroughly investigated. The [Bmim]OAc pretreatment promoted the separation of hemicelluloses with relatively high molecular weights in the following alkali extractions, accompanying with slightly structural changes. The alkali-soluble hemicelluloses obtained from Eucalyptus are characterized to be a linear backbone of (1 → 4)-linked-β-D-xylopyranosyl residues decorated with branch at O-2 of 4-O-methyl-α-glucuronic acid unit. Additionally, the thermal stability of hemicelluloses was also increased by the ionic liquids pretreatment.

Effect of ionic liquids pretreatment on thermal degradation kinetics of agro-industrial waste reinforced thermoplastic starch composites

Converting agricultural lignocellulosic waste into marketable composite product is a promising approach to protect the environment and earn financial gain. Ionic liquids (ILs) have emerged as the innovative and effective solvents for pretreatment of lignocellulosic materials to produce potential reinforcements for biocomposite manufacturing. Kinetic predictions are particularly essential for practical utilization of kinetic analysis for process design and to assess the performance of composite product during service life. This work aims to explore the impact of ILs assisted pretreatment of oil palm biomass on the thermal degradation kinetics of their fabricated biocomposites with thermoplastic starch as polymer matrix. The approach combines the pretreatment of oil palm frond (OPF) fiber with ILs 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-ethyl-3-methylimidazolium diethylphosphate ([Emim][dep]) prior to fabricate thermo-molded composite panels. Flynn–Wall–Ozawa method based on the model-free isoconversional approach was chosen to predict the activation energy of the biocomposites. Further, the influence of ILs pretreatment on physico-chemical properties of the OPF fiber was assessed by lignocellulosic characterization and crystallinity measurement. The results indicated that composites prepared with ILs pretreated OPF fiber exhibited 10–125% higher activation energy as compared to untreated composite over a conversion range of α=0.1–0.6. Characterization of the untreated and pretreated fibers by examining the lignocellulosic fraction and analyzing the degree of crystallinity evidenced that ILs pretreatment increased the cellulose contents by 1.5–1.8 folds and caused significant reduction in the crystallinity of the OPF fiber. The present findings plainly indicate the promising potential of ILs based pretreatment as a new and clean processing approach for manufacturing of engineered composite panels from agricultural waste.

Survey of Lignin-Structure Changes and Depolymerization during Ionic Liquid Pretreatment

A detailed study of chemical changes in lignin structure during the ionic liquid (IL) pretreatment process is not only pivotal for understanding and overcoming biomass recalcitrance during IL pretreatment but is also necessary for designing new routes for lignin valorization. Chemical changes in lignin were systematically studied as a function of pretreatment temperature, time, and type of IL used. Kraft lignin was used as the lignin source, and common pretreatment conditions were employed using three different ILs of varying chemical structure in terms of acidic or basic character. The chemical changes in the lignin structure due to IL pretreatment processes were monitored using 1H–13C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR), 31P NMR, elemental analysis, gel permeation chromatography (GPC), and Fourier transform infrared (FT-IR), and the depolymerized products were analyzed using gas chromatography mass spectrometry (GC-MS). Although, with pretreatment in acidic IL,...

Effect of Ionic Liquid Pretreatment on the Porosity of Pine: Insights from Small-Angle Neutron Scattering, Nitrogen Adsorption Analysis, and X-ray Diffraction

Small-angle neutron scattering (SANS) was used to study the porosity of pine samples before and after ionic liquid (IL) pretreatment. Pine samples were pretreated using 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]) at 110 °C for 3 h at biomass concentrations of 5, 10, 15, 20, and 25 wt % and at 130 °C for 3 h at biomass concentrations of 5 and 25 wt %. For the first time, relative changes in porosity of pretreated pine samples derived from SANS were compared with those obtained from the nitrogen adsorption analysis. Biomass crystalline structures were measured by X-ray diffraction (XRD). Both porosity and XRD data suggest that [C2C1Im][OAc] interacted with pine samples more efficiently at higher biomass concentrations during pretreatment. This was attributed to the presence of resin acid in the pine samples.

Unraveling variations of crystalline cellulose induced by ionic liquid and their effects on enzymatic hydrolysis

Ionic liquid (IL) is one of the pretreatment processes gaining considerable interests to remove the native recalcitrance of lignocellulose. But the cellulose crystalline transformation during the pretreatment and their correlations with enzymatic digestibility have not been fully elucidated. Microcrystalline cellulose (Avicel) and holocellulose, which have differential sources and original crystallinity, were respectively pretreated with 1-butyl-3-methylimidazolium chloride ([C4min]Cl). Cellulose crystalline variations as well as chemical and morphological changes were determined. Crystallinity of different materials was proved to influence the effects of pretreatment and following enzymatic digestibility. Recrystallized cellulose Iβ was revealed from slight initial cellulose Iα of Avicel, which was accomplished via formation of intermediate paracrystalline phases. The conversion yield of IL pretreated Avicel displayed no obvious changes, mainly resulted from initial high crystalline order and the recrystallization behavior. Recalcitrance of holocellulose was destroyed during cellulose allomorph transformation and hemicelluloses extraction, contributing to significant increase of glucose yield up to 92.20%. Explicit comprehension on cellulose supramolecular structure may help provide more efficient process for bioconversion after IL pretreatment.

Variations in Physicochemical Properties and Bioconversion Efficiency of Ulva lactuca Polysaccharides After Different Biomass Pretreatment Techniques.

Green macroalgae are an abundant and undervalued biomass with a specific cell wall structure. In this context, different pretreatments, namely ethanol organosolv (Org), alkaline, liquid hot water (LHW), and ionic liquid (IL) pretreatments, were applied to the green macroalgae Ulva lactuca biomass and then evaluated. Their effects on chemical composition, biomass crystallinity, enzymatic digestibility, and theoretical ethanol potential were studied. The chemical composition analysis showed that the Org and LHW pretreatments allowed the highest glucan recovery (80.8±3.6 and 62.9±4.4g/100g DM, respectively) with ulvan (80.0 and 99.1%) and hemicellulose (55.0 and 42.3%) removal. These findings were in agreement with both thermogravimetric analysis and scanning electron microscopy results that confirm significant structural changes of the pretreated biomasses. It was found that the employed pretreatments did not significantly affect the cellulose crystallinity; however, they both increased the whole crystallinity and the enzymatic digestibility. This later reached 97.5% in the case of LHW pretreatment. Our results showed high efficiency saccharification of Ulva lactuca biomass that will constitute the key step of the implementation of a biorefinery process.

Impact of Dilute Sulfuric Acid, Ammonium Hydroxide, and Ionic Liquid Pretreatments on the Fractionation and Characterization of Engineered Switchgrass

Improving plant characteristics for better environmental resilience and more cost-effective transformation to fuels and chemicals is one of the focus areas in biomass feedstock development. In order to bridge lignin engineering and conversion technologies, this study aimed to fractionate and characterize lignin streams from wild-type and engineered switchgrass using three different pretreatment methods, i.e., dilute sulfuric acid (DA), ammonium hydroxide (AH), and aqueous ionic liquid (IL). Results demonstrate the low lignin content and high S/G ratio switchgrass mutant (4CL) was more susceptible to pretreatment and subsequently more digestible by enzymes as compared to wild-type switchgrass and AtLOV1 mutant. In addition, when compared to DA and AH pretreatment, aqueous IL (cholinium lysinate) was demostrated to be an efficient lignin solvent, as indicated by the high (> 80%) lignin solubility and reduced lignin molecular weight. FTIR and differential scanning calorimetry measurements suggest that pretreatment chemistry greatly influenced the structural and compositional changes and thermal properties of the pretreated switchgrass and recovered lignin-rich streams. The comparative data obtained from this work deepen our understanding of how lignin modification impacts the fractionation and properties of biomass feedstocks.

Investigation of accessibility and reactivity of cellulose pretreated by ionic liquid at high loading

High loading of cellulose in ionic liquid (IL) pretreatment is potentially a key technique for cellulose conversion to glucose in biorefining. In this work, to expand the potential use of this high loading technique, the accessibility of microcrystalline cellulose pretreated with an IL across a wide cellulose loading range (5–50mol%) and its relationship with the hydrolytic reactivity were comprehensively investigated. The results show that the estimated cellulose accessibility based on the crystallinity and specific surface area was notably higher in 25mol% loading than that for a conventional loading of 5mol%. Consistently, acid-catalyzed glucose conversion was faster at this high loading, showing that a higher cellulose loading improves the pretreatment efficiency. In contrast, enzymatic hydrolysis was not enhanced by a high cellulose loading. A key difference between the activities in these two hydrolytic reactions is the catalyst size.

Microwave-Assisted Simplified Simultaneous Distillation Coupled with Ionic Liquid Pretreatment for the Analysis of Essential Oil in Schisandra sphenanthera.

Simultaneous distillation extraction (SDE) is quite useful for the separation of volatile compounds from an analyte when their contents are quite low. In this study, a simplified SDE approach is applied for the extraction of essential oil from Schisandra sphenanthera, with microwave as heating source, [Bmim][Cl] as the medium for pretreatment, and gas chromatography-mass spectrometry as the analytical approach. Consequently, the improvement resulted from [Bmim][Cl] pretreatment is demonstrated by taking comparison with blank experiments. Totally 61 compounds have been detected in the essential oil obtained by using [Bmim][Cl] pretreatment, while without [Bmim][Cl] pretreatment, only 53 compounds can be detected. Moreover, [Bmim][Cl] pretreatment can also resulted in a higher yield of essential oil. The experimental results demonstrate that the simplified SDE coupled with ionic liquid pretreatment is a feasible approach for the extraction of essential oil from S. sphenanthera with high efficiency as 0.85% of essential oil yield has been obtained, and can be potentially extended to the extraction of essential oil or other target volatile compounds with low content.