Deconstruction of lignocellulosic biomass with ionic liquids

In the paper

“A protic cation prevents cellulose solubilisation entirely in many cases.57,91”

What the sources say

• Not checked yetcites [57] source
• Not checked yetcites [91] source

In the paper

“Despite these difficulties, the tabulated data show that [C 2 C 1 im][MeCO 2 ] is capable of partially removing both hemicellulose and lignin simultaneously.”

In the paper

“The choice of cation also affects solubility considerably.”

In the paper

“For [C 4 C 1 im][HSO 4 ], and also for its acid-base ionic liquid analogue [C 4 Him][HSO 4 ], the delignification seems to be more extensive than with [C 2 C 1 im]-[MeCO 2 ].”

In the paper

“Lengthening the alkyl (or glycol) chains on the cation progressively reduces cellulose solubility.”

In the paper

“Although the measurements were performed under a variety of conditions (e.g.different temperature, dissolution time, cellulose degree of polymerisation, moisture content, ionic liquid purity), which affect the maximum solubility, the importance of a high β value (>0.8) is apparent.”

In the paper

“Less extensive delignification and hemicellulose removal is generally achieved for softwood ( pine) feedstocks compared to herbaceous and hardwood lignocellulose.”

In the paper

“Hydroxyl groups on the alkyl chains, functionalities that increase the hydrogen-bond acidity of the ionic liquid, also reduce the solubility of cellulose.”

In the paper

“The ionic liquid [C 4 C 1 pyrr][MeCO 2 ], based on an aliphatic (cyclic) ammonium cation, which usually show lower resistance to decomposition than imidazolium cations, decomposed completely within just 30 h at 120 °C.”

In the paper

“Wang et al. reused [CvC 2 C 1 im]Cl once after a dissolution treatment of 5 wt% pine and did not detect any reduction in performance.121”

What the sources say

• Not checked yetcites [121] source

In the paper

“Optimisation of the carbohydrate yield after deconstructing wheat straw with a [C 2 C 1 im][MeCO 2 ] process using the Design of Experiment (DOE) approach resulted in an optimal process temperature of 158 °C.175”

What the sources say

• Not checked yetcites [175] source

In the paper

“It is important to note that the majority of biomass deconstruction experiments using these ionic liquids have been performed at temperatures greatly in excess of this limit.”

In the paper

“This was at 50.5 wt% water content, where the effect of water on the ionic liquid is likely to be considerable.”

What the sources say

• Not checked yetcites [175] source

In the paper

“It has been shown that anions that are very nucleophilic, such as chloride and acetate, can lower T onset to around 200 °C, while dissolved cellulose appears to have no effect on the IL decomposition temperature, even up to 12% cellulose.74”

What the sources say

• Not checked yetcites [74] source

In the paper

“Due to the lack of data in the literature, we measured T 0.01/10 h for [C 4 C 1 im][MeCO 2 ] and determined it as 102 °C.174”

What the sources say

• Not checked yetcites [174] source

In the paper

“Decomposition of [C 2 C 1 im]-[MeCO 2 ] and [C 2 C 1 im]Cl at 100-130 °C was almost complete within 4 months.177”

What the sources say

• Not checked yetcites [177] source

In the paper

“It has been shown that anions that are very nucleophilic, such as chloride and acetate, can lower T onset to around 200 °C, while dissolved cellulose appears to have no effect on the IL decomposition temperature, even up to 12% cellulose.74”

What the sources say

• Not checked yetcites [74] source

In the paper

“It has been shown that the economic viability of ionic liquid deconstruction is very sensitive to the efficiency of ionic liquid recycling and therefore decomposition must be avoided.171”

What the sources say

• Not checked yetcites [171] source

In the paper

“Data from deconstruction experiments support this: Rogers and co-workers have observed 15% weight loss within 10 min when treating bagasse and pine with [C 2 C 1 im][MeCO 2 ] at 185 °C.119”

What the sources say

• Not checked yetcites [119] source

In the paper

“Another study reused [C 4 C 1 im]Cl 7 times for fractionation of legume straw with ionic liquid water mixtures.140”

What the sources say

• Not checked yetcites [140] source

In the paper

“The biomass type also plays a role with regard to the energy consumption of grinding, with grasses requiring less grinding energy than woody biomass.184”

What the sources say

• Not checked yetcites [184] source

In the paper

“In addition, higher pulp recoveries were observed when the ionic liquid was reused, which could be due to less extensive lignin removal.”

What the sources say

• Not checked yetcites 129b

In the paper

“Li et al. reused [CvC 2 C 1 im]Cl three times for deconstructing 8 wt% Eucalyptus using the Dissolution Process and found that the saccharification yields decreased progressively.129b”

What the sources say

• Not checked yetcites 129b

In the paper

“For example, it was shown that more than 10% of the energy contained in willow was required for grinding air-dried chips to a particle size of <1 mm.184”

What the sources say

• Not checked yetcites [184] source

In the paper

“Rogers and co-workers reused [C 2 C 1 im][MeCO 2 ] once after treatment of 4.8 wt% bagasse at 185 °C for 10 min; 119 the delignification efficiency dropped from 63% to 38%.”

What the sources say

• Not checked yetcites [119] source

In the paper

“A recent study shows that ionic liquids could help to reduce the energy input for grinding wood-derived lignocellulose.”

What the sources say

• Not checked yetcites [187] source

In the paper

“The energy input to grinding for corn stover conversion was estimated to be 1.1% of the energy content of corn stover (0.186 GJ of 17.0 GJ per tonne).185”

What the sources say

• Not checked yetcites [185] source

In the paper

“The savings were shown to be due to the lubricating properties of ionic liquids, rather than partial modification of the lignocellulose matrix.”

What the sources say

• Not checked yetcites [187] source

In the paper

“In spite of this, almost quantitative removal of lignin has been achieved.55”

What the sources say

• Not checked yetcites [55] source

In the paper

“The ionic liquid [C 2 C 1 im]Cl also affects growth of the yeast, but to a lesser extent.188”

What the sources say

• Not checked yetcites [188] source

In the paper

“The ionic liquids used for biomass dissolution are highly hydroscopic (Fig. 21).”

In the paper

“Careful analysis of the ionic liquids that are actually used in the chemicals processing industry on a large scale shows that they are mostly based on protic cations, such as [C 1 Him] + , usually combined with a mineral acid derived anion, such as Cl -.”

In the paper

“The most effective ionic liquid so far has been [C 2 C 1 im][MeCO 2 ].”

In the paper

“Although there has very recently been an increased interest in the conversion of lignin into chemicals, 9 to date there are no available commercial processes for this upgrading.”

What the sources say

• Not checked yetcites [9] source

In the paper

“The study found that water was more effective in removing residual ionic liquid than either pure ethanol or acetone-ethanol mixtures.”

What the sources say

• Not checked yetcites [195] source

In the paper

“The chloride ions also inhibit enzymatic activity in concentrations of less than 1%.195”

What the sources say

• Not checked yetcites [195] source

In the paper

“The first techno-economical analysis modelling of ionic liquid deconstruction has determined that among the investigated variables the order of importance/ sensitivity is ionic liquid price > biomass loading > recycling rate.171”

What the sources say

• Not checked yetcites [171] source

In the paper

“As little as 0.25% residual [C 2 C 1 im][MeCO 2 ] in the fermentation broth will completely inhibit yeast growth and biofuel production.188”

What the sources say

• Not checked yetcites [188] source

In the paper

“Lignin precipitation requires more water than is generally used to precipitate cellulose from the Dissolution Process solutions.”

In the paper

“In spite of this complaint, for other applications, ionic liquids have been applied as process solvents on a large scale.51”

What the sources say

• Not checked yetcites [51] source

In the paper

“The lignin crust has been identified as one of the major obstacles for an energy-efficient biomass deconstruction process.8”

What the sources say

• Not checked yetcites [8] source

In the paper

“Native lignin not only prevents access of polysaccharide hydrolases to their substrates, but modified lignin adhering to the pulp after pretreatment also causes unproductive binding of hydrolases.25”

What the sources say

• Not checked yetcites [25] source

In the paper

“Lignocellulosic biomass is the most abundant plant material on our planet and therefore available in much higher quantities (also due to higher yields per area of land) and at lower cost than starch and sucrose based materials.1c,4”

What the sources say

• Not checked yetcites 1c,4

In the paper

“A major obstacle to competitive lignocellulose utilisation is that cost-effective technologies for processing lignocellulosic material into fuels and chemicals are yet to be commercially developed.6”

What the sources say

• Not checked yetcites [6] source

In the paper

“Lignocellulosic biomass is the most abundant plant material on our planet and therefore available in much higher quantities (also due to higher yields per area of land) and at lower cost than starch and sucrose based materials.1c,4”

What the sources say

• Not checked yetcites 1c,4

In the paper

“This paper reviews the application of ionic liquids to the deconstruction and fractionation of lignocellulosic biomass, in a process step that is commonly called pretreatment.”

In the paper

“The deconstruction of lignocellulose is likely to account for an important fraction of the energy requirement for biomass processing.8”

What the sources say

• Not checked yetcites [8] source

In the paper

“Lignocellulosic biomass is the most abundant plant material on our planet and therefore available in much higher quantities (also due to higher yields per area of land) and at lower cost than starch and sucrose based materials.1c,4”

What the sources say

• Not checked yetcites 1c,4

In the paper

“It has been estimated that the US produces enough lignocellulosic feedstock today to substitute 30% of their liquid transport fuels with biofuels.4”

What the sources say

• Not checked yetcites [4] source

In the paper

“Utilisation of lignocellulose as a biofuel feedstock is likely to provide much higher CO 2 emission savings.2,5”

What the sources say

• Not checked yetcites [2] source
• Not checked yetcites [5] source

In the paper

“A relatively high lignin content combined with a high guaiacyl to syringyl ratio in the lignin is considered to be the reason for its higher resistance to delignification compared to grass or hardwood biomass.”

In the paper

“Thus, these cross-links must be broken by chemically hydrolysing the ester bonds in order to obtain an effective deconstruction process.31”

What the sources say

• Not checked yetcites [31] source

In the paper

“Ferulic acid can also dimerise hemicellulose chains (Fig. 10).”

In the paper

“The utilisation of the pentoses, particularly xylose, will improve the economics of biofuel production.42”

What the sources say

• Not checked yetcites [42] source

In the paper

“This structure also affects the diffusion of chemicals into and out of wood chips during chemical deconstruction.33”

What the sources say

• Not checked yetcites [33] source

In the paper

“In grasses, these lignin-carbohydrate complexes contain ferulic acid (Fig. 9).”

What the sources say

• Not checked yetcites [28]

In the paper

“Although this feedstock is very abundant, it is also the most recalcitrant feedstock type.”

In the paper

“This also results in significantly accelerated hydrolysis with cellulases compared to native cellulose, 77 an effect that is very attractive in terms of the biorefinery and has sparked interest in the use of cellulose dissolving ionic liquids in lignocellulose deconstruction.”

What the sources say

• Not checked yetcites [77] source

In the paper

“The extent of cross-linking via lignin-carbohydrate complexes has been correlated with increased cell wall rigidity and resistance to enzymatic digestion.”

In the paper

“In softwood and hardwood, direct complexes between lignin and carbohydrates are present.32”

What the sources say

• Not checked yetcites [32] source

In the paper

“Lignin can also be a source of compounds that inhibit hydrolases and fermentative organisms, including syringyl aldehyde and vanillic acid.26”

What the sources say

• Not checked yetcites [26] source

In the paper

“It has been observed that the ionic liquid anion plays an important role in determining an ionic liquid's ability to dissolve cellulose.69a”

What the sources say

• Not checked yetcites 69a

In the paper

“Native lignin not only prevents access of polysaccharide hydrolases to their substrates, but modified lignin adhering to the pulp after pretreatment also causes unproductive binding of hydrolases.25”

What the sources say

• Not checked yetcites [25] source

In the paper

“Ferulic acid is initially bonded to hemicellulose (arabinoxylan) via ester bonds.28”

What the sources say

• Not checked yetcites [28]

In the paper

“These processes are optimised for high cellulose yield and fibre strength, which are required for paper production.This does not match the needs of the biorefinery industry, which needs high quality fermentable sugar solutions at extremely low cost, and highpurity by-product streams that add value.”

In the paper

“In addition, the recovery of non-fermentable components as co-products, particularly lignin, will allow multiple revenue streams compared to a single fermentation product. 1”

What the sources say

• Not checked yetcites [1] source

In the paper

“More recently, it has been demonstrated that a range of ionic liquids, typically with 1,3-dialkylimidazolium cations, are also effective cellulose solvents.69”

What the sources say

• Not checked yetcites [69] source

In the paper

“The dissolving power of these relevant ionic liquids has been typically attributed to strong hydrogen-bonding interactions between the anions and equatorial hydroxyl groups on the cellulose.”

In the paper

“The order of molecular weight reduction was sulfates > lactate > acetate > chloride > phosphates.”

What the sources say

• Not checked yetcites [134] source

In the paper

“Therefore it appears, as one might expect, that water tolerance is dependent on the nature of the ionic liquid.”

In the paper

“The enol ether product in Fig. 23 (top) was observed as an intermediate when the ionic liquid contained a coordinating anion.”

What the sources say

• Not checked yetcites [142] source

In the paper

“As a potential drawback, the less basic or sometimes even acidic environment of non-acetate ionic liquids can cause more hemicellulose conversion to furfurals and/or humins, which is not seen for the acetate ionic liquids.55”

What the sources say

• Not checked yetcites [55] source

In the paper

“Differences in reactivity depending on the anion were observed.”

What the sources say

• Not checked yetcites [142] source

In the paper

“These findings also agree with empirical solvent polarity measurements, which are applied to predict solvent properties, among others, rate constants and solubility.46a”

What the sources say

• Not checked yetcites 46a

In the paper

“Suitable ionic liquids identified to date contain anions that can form strong hydrogen bonds with hydroxyl groups, e.g.chloride, 69a carboxylates (acetate, formate, propionate, lactate), 78 dialkyl phosphates, dialkyl and trialkylphosphonates 69d and amino acid anions.79”

What the sources say

• Not checked yetcites 69a
• Not checked yetcites [78] source
• Not checked yetcites 69d,79

In the paper

“In ionic liquids, particularly those with non-functionalised cations such as dialkylimidazolium, the hydrogen-bond basicity/value of β is primarily influenced by the anion.56”

What the sources say

• Not checked yetcites [56] source

In the paper

“Therefore, the ionic liquids treatments typically lead to enrichment of cellulose in the recovered solids.”

In the paper

“In support of this, an increased sulfur content of the lignin after treatment with ionic liquids with sulfur containing anions such as sulfonates and sulfamates (e.g.[ABS] -and acesulfamate) 52,53 and sulfates ([MeSO 4 ] -and [HSO 4 ] -) 55 has been reported.”

What the sources say

• Not checked yetcites [52] source
• Not checked yetcites [53] source
• Not checked yetcites [55] source

In the paper

“Less coordinating anions such as [BF 4 ] -resulted in elimination of the γ hydroxyl methylene group, resulting in formation of formaldehyde.”

What the sources say

• Not checked yetcites [142] source

In the paper

“The oxidation of Organosolv beech lignin in ionic liquids in the presence of transition metals and molecular oxygen has been demonstrated by Stärk et al. 143”

What the sources say

• Not checked yetcites [143] source

In the paper

“This close association was confirmed by NMR studies on ionic liquid solutions of glucose and cellobiose 81 and molecular dynamics studies of the interaction of [C 2 C 1 im][MeCO 2 ] 82 or [C 4 C 1 im]Cl 83 with celloligomers.”

What the sources say

• Not checked yetcites [81] source
• Not checked yetcites [82] source
• Not checked yetcites [83] source

In the paper

“The 1 H-NMR spectral shift of the ethanol hydroxyl proton peak in the presence of ionic liquids has been correlated with the cellulose solubilisation power of imidazolium ionic liquids.84”

What the sources say

• Not checked yetcites [84] source

In the paper

“Ionic liquids with more exotic hydrogen-bond basic anions, such as phosphorthioates or phosphorselenoates, have proven to be less stable than the earlier discoveries.80”

What the sources say

• Not checked yetcites [80] source

In the paper

“For cellulose solubility, it was shown that ionic liquids that dissolve cellulose are characterised by high values for parameters describing solvent hydrogen-bond basicity.”

In the paper

“An α,β-dehydration reaction was reported for both ionic liquids.”

What the sources say

• Not checked yetcites [135] source

In the paper

“Therefore sulfonate and sulfate containing ionic liquids appear to be the currently most potent ionic liquids in terms of separating cellulose from lignin (and hemicelluloses).”

In the paper

“The dehydration was significantly faster in [C 2 C 1 im][MeCO 2 ] than in [C 2 C 1 im]Cl, possibly reflecting the acetate's greater basicity and affinity towards water.141”

What the sources say

• Not checked yetcites [135] source

In the paper

“Since the anion and the cation core are very similar for [C 4 C 1 im][MeCO 2 ] and [C 2 C 1 im][MeCO 2 ], the T 0.01/10 h for [C 2 C 1 im][MeCO 2 ] is anticipated to be very similar.”

In the paper

“It has been shown that the economic viability of ionic liquid deconstruction is very sensitive to the efficiency of ionic liquid recycling and therefore decomposition must be avoided.171”

What the sources say

• Not checked yetcites [171] source

In the paper

“This would result in a maximum process temperature of ca.90 °C for both of these very commonly used ionic liquids.”

In the paper

“The latter two ionic liquids can dissolve cellulose, but the relatively high basicity of their anions, which are both counter-ions of weak acids (with pK a values of 1.29 155 for dimethyl phosphoric acid and 4.76 for acetic acid) reduces the acidity of these solutions so much that glucose production cannot be observed.”

What the sources say

• Not checked yetcites 146a

In the paper

“Almost quantitative yield of glucose and cellobiose with very little HMF was achieved when hydrolysing pure cellulose in acidified [C 4 C 1 im]Cl with the incremental water method.149”

What the sources say

• Not checked yetcites [149] source

In the paper

“Lignocellulose deconstruction with ionic liquids will only be successful if the ionic liquid can be recycled, due to the high solvent cost.”

In the paper

“When acidic protons are present in a mixture of proton acceptors the weaker acid always forms.”

In the paper

“In ionic liquids with basic anions, such as [C 2 C 1 im][MeCO 2 ], the hemicellulose remains largely oligomeric, 136 which is typical for alkaline deconstruction processes.”

What the sources say

• Not checked yetcites [136] source

In the paper

“The decrease of the monomer yield at higher water content is probably due to decreased lignocellulose solubility.”

What the sources say

• Not checked yetcites 129a

In the paper

“This partial degradation affects the recycling efficiency as well as the properties of the ionic liquid as degradation products accumulate.”

In the paper

“This gives rise to 'solvent levelling' of the acidity, with the ionic liquid anion playing the role of the solvent's basic functional group.”

In the paper

“The use of [C 4 C 1 im][MeCO 2 ] led to destruction of the heterogeneous catalysts.”

What the sources say

• Not checked yetcites [152]

In the paper

“This is likely due to the limited amount of water available in the anhydrous system, halting the hydrolysis at the oligomer stage.”

What the sources say

• Not checked yetcites 129a

In the paper

“Similarly to soluble acids, the production of short cellulose oligomers was observed rather than complete hydrolysis to monomers.”

What the sources say

• Not checked yetcites [152]

In the paper

“The best conditions (using a 1 : 3 ration of NMP to ionic liquid) resulted in a 69% total reducing sugar yield and 39% glucose yield.”

What the sources say

• Not checked yetcites [150] source

In the paper

“Performing the (chemical) hydrolysis of cellulose and hemicellulose while dissolved in an ionic liquid has the advantage that the glycosidic bonds are more accessible in homogenous solution, allowing milder hydrolysis conditions.”

In the paper

“As already mentioned, the long-term thermal stability of the ionic liquid under process conditions will be important for the near-quantitative recycling.”

In the paper

“The product solution was not analysed for degradation products or lignin.”

What the sources say

• Not checked yetcites [150] source

In the paper

“Lignocellulose deconstruction with ionic liquids typically involves heatingin many studies well above 100 °C (up to 190 °C has been reported).52,119”

What the sources say

• Not checked yetcites [52] source
• Not checked yetcites [119] source

In the paper

“Although this is a start, one repeat is not sufficient to assess performance on an industrial scale where many cycles will be necessary to make an ionic liquid deconstruction process viable.”

In the paper

“It is also likely that this is where the extractable organic small molecules will be found (oils, acetic acid, ferulic acid, vanillin, other small lignin fragments, furfurals, levulinic acid etc.).”

In the paper

“Therefore, it is by cation design that an ionic liquid could be optimised for washing.”

In the paper

“The preliminary observations that fractionation and, in some cases, the saccharification are somewhat adversely affected by repeated use of the ionic liquid suggests that a clean-up step is likely to be necessary.”

In the paper

“However, the larger the ratio between initial and final particle size, the more mechanical energy is required for the size reduction, all other conditions being equal.183”

What the sources say

• Not checked yetcites [183] source

In the paper

“These studies show results for the changing performance of the ionic liquids in the process step in which they were used, not the condition of the ionic liquid solution that was being recycled.”

In the paper

“In contrast, hardwoods and softwoods may require prohibitive quantities of energy to grind to fine powders.183,186”

What the sources say

• Not checked yetcites [183] source
• Not checked yetcites [186] source

In the paper

“For the Ionosolv, as well as the Dissolution Process, it is important that the cellulose fraction be as free of ionic liquid as possible to avoid unwanted deactivation of the saccharification enzymes 162 or toxicity to the fermenting microorganisms.188”

What the sources say

• Not checked yetcites [162] source
• Not checked yetcites [188] source

In the paper

“Water can be added to the ionic liquid phase to precipitate the dissolved lignin for further processing or incineration.52,53,55”

What the sources say

• Not checked yetcites [52] source
• Not checked yetcites [53] source
• Not checked yetcites [55] source

In the paper

“As has been noted above, the solubility of cellulose in the ionic liquids used in the Dissolution Process is sensitive to the presence of water.”

In the paper

“Even the lower end of this temperature range coincides with some degradation of [C 2 C 1 im][MeCO 2 ] on these timescales (see above).”

In the paper

“In addition, the ability to sell the lignin and/or its products will heavily impact on the process costs.”

In the paper

“For the Ionosolv Process to be viable, it will be necessary to reconcentrate the ionic liquid for reuse.”

In the paper

“This makes these ionic liquids much cheaper than those with fully alkylated cations (e.g.[C 2 C 1 im] + in [C 2 C 1 im][MeCO 2 ]) used in most academic laboratories.”

In the paper

“Since good cellulose solubility (Fig. 18) has been related to the ionic liquid anion's β value in the same way as its hydrophilicity (Fig. 21), we cannot see a way to address this problem through ionic liquid design.”

In the paper

“This is made possible by the relatively acidic nature of the ionic liquid, which keeps the dissolved lignin in fully protonated form ( phenol groups rather than phenolates).”

In the paper

“Unless drying is a prominent feature of the process, the build-up of water in the ionic liquid will lead to levels that will prevent cellulose dissolution and hence stop the process.”

In the paper

“However, deconstruction with ionic liquid will only be viable if its advantages outweigh the drawbacks of ionic liquids, most prominently the cost of ionic liquids relative to the value of the substrate processed by them.”

In the paper

“As already mentioned, a major and widely highlighted advantage of the ionic liquid Dissolution Process compared to other pretreatment options is its ability to decrystallise the cellulose portion of lignocellulosic biomass and simultaneously disrupt the lignin and hemicellulose network.”