Publications
51 results found
Castillo Castillo A, Brophy K, Hallett J, et al., 2023, Addressing plastic additives, London, Publisher: Institute for Molecular Science and Engineering, Briefing topic No. 10
Hundreds of chemicals with known toxicity to humans and the environment are still widely used as additives in plastics. The average consumer’s knowledge of what goes into plastic products is not sufficient to make informed choices about exposure. The data collection needed to make these choices often does not exist, especially for recycled products made of mixtures of existing plastics. Though data on the toxicology of single additives in isolation may be available, there is very little data on the interaction of multiple additives in real world situations, either within a single product or between many products in a single place. Most substances are not restricted until proven toxic. As a result, damage comes first and action second. Substance-by-substance testing often results in the substitution of one hazardous molecule by another with similar toxicology. Governments and consumers should demand the use of non-toxic chemicals for use in plastics, especially given the risk of admixture of toxic substances in recycled plastic products. Consumers and producers should demand full supply chain transparency on additive presence in plastic products. Understanding the toxicology of mixtures of additives requires the generation of substantial new datasets. This data should include biomonitoring to characterise the complexity of real-world exposures. Assessments of toxicity should not assume that a low dose always means a low risk. Hazardous substances should be regulated by group rather than one-by-one to avoid substituting one harmful chemical for another. A molecular science and engineering approach is crucial to finding chemical and functional alternatives to toxic additives, and also for developing new processes to better manage the toxicity of additives which cannot be replaced or omitted.
Yang SM, Shaffer MSP, Brandt-Talbot A, 2023, High Lignin Content Carbon Fiber Precursors Wet-Spun from Low-Cost Ionic Liquid Water Mixtures, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 11, Pages: 8800-8811, ISSN: 2168-0485
Barbara PV, Rafat AA, Hallett JP, et al., 2023, Purifying cellulose from major waste streams using ionic liquids and deep eutectic solvents, CURRENT OPINION IN GREEN AND SUSTAINABLE CHEMISTRY, Vol: 41, ISSN: 2452-2236
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Bukowski A, Schnepf K, Wesinger S, et al., 2022, Sensitivity analysis and parameter optimization for the fractionative catalytic conversion of lignocellulosic biomass in the polyoxometalate–ionosolv concept, ACS Sustainable Chemistry and Engineering, Vol: 10, Pages: 8474-8483, ISSN: 2168-0485
The recently developed polyoxometalate (POM)–ionosolv concept offers an interesting strategy to generate two valuable product streams from lignocellulosic biomass, a solid cellulose-rich pulp and short-chain carboxylic acids like formic acid and acetic acid in a simple and cost-efficient manner. This study aimed to find optimum parameters for the two steps of the transformation by performing a sensitivity analysis on the initial ionosolv fractionation step as well as kinetic investigations of the following POM-catalyzed oxidation step. The results were transferred to the POM–ionosolv concept to find the overall process optimum. Beech wood was used as an industrially relevant substrate for ionosolv fractionation with the low-cost ionic liquid triethylammonium sulfate, [TEA][HSO4], and the HPA-5 [H8PV5Mo7O40] POM catalyst for the oxidation of the dissolved components in an oxygen atmosphere. As the most seminal finding, we defined optimum conditions of 125 °C, 1200 rpm, 30 bar oxygen, and 24 h reaction time in ionic liquid containing 70% water, achieving 72% xylose extraction from beech wood, which resulted in a 39% formic acid yield. We suggest that the fractionation and catalytic conversion are carried out at different water contents for maximum conversion efficiency for each step.
Titirici M, Baird SG, Sparks TD, et al., 2022, The sustainable materials roadmap, Journal of Physics: Materials, Vol: 5, Pages: 1-98, ISSN: 2515-7639
Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as
Gschwend FJ, Hennequin LM, Brandt-Talbot A, et al., 2020, Towards an environmentally and economically sustainable biorefinery: heavy metal contaminated waste wood as a low-cost feedstock in a low-cost ionic liquid process, Green Chemistry, Vol: 22, Pages: 5032-5041, ISSN: 1463-9262
In the present study, we used a low-cost protic ionic liquid, 1-methylimidazolium chloride, to simultaneously fractionate heavy metal contaminated wood and extract the metals from the wood at elevated temperature and short reaction time. This treatment selectively dissolves the lignin and hemicellulose in the biomass, leaving a solid cellulose-rich pulp, while coordinating and extracting 80–100% of the metal species present in the wood in a one-pot process. The lignin stream was recovered from the liquor and the cellulose was hydrolysed and then fermented into ethanol. The ionic liquid was recycled 6 times and the metals were recovered from the liquor via electrodeposition. This is the first time that highly contaminated waste wood has been integrated into a process which does not produce a contaminated waste stream, but instead valorises the wood as a feedstock for renewable chemicals, materials and fuels, while efficiently recovering the metals, converting a toxic environmental hazard into a rich source of biorenewables. We have therefore used an otherwise problematic waste as a low-cost lignocellulsoic feedstock for a circular bioeconomy concept.
Nakasu PYS, Clarke CJ, Rabelo SC, et al., 2020, Interplay of Acid–Base Ratio and Recycling on the Pretreatment Performance of the Protic Ionic Liquid Monoethanolammonium Acetate, ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 7952-7961
Gschwend FJV, Hallett JP, Brandt-Talbot A, 2020, Exploring the effect of water content and anion on the pretreatment of poplar with three 1-Ethyl-3-methylimidazolium ionic liquids, Molecules, Vol: 25, Pages: 2318-2318, ISSN: 1420-3049
We report on the pretreatment of poplar wood with three different 1-ethyl-3-methylimidazolium ionic liquids, [EMim][OAc], [EMim][MeSO3], and [EMim][HSO4], at varying water contents from 0–40 wt% at 100 °C. The performance was evaluated by observing the lignin and hemicellulose removal, as well as enzymatic saccharification and lignin yield. The mechanism of pretreatment varied between the ionic liquids studied, with the hydrogen sulfate ionic liquid performing delignification and hemicellulose hydrolysis more effectively than the other solvents across the investigated water content range. The acetate ionic liquid produced superior glucose yield at low water contents, while the hydrogen sulfate ionic liquid performed better at higher water contents and produced a recoverable lignin. The methanesulfonate ionic liquid did not introduce significant fractionation or enhancement of saccharification yield under the conditions used. These findings help distinguish the roles of anion hydrogen bonding, solvent acidity, and water content on ionic liquid pretreatment and can aid with anion and water content selections for different applications.
Tu W-C, Weigand L, Hummel M, et al., 2020, Characterisation of cellulose pulps isolated from Miscanthus using a low-cost acidic ionic liquid, Cellulose, Vol: 27, Pages: 4745-4761, ISSN: 0969-0239
The ionoSolv pretreatment generates a cellulose pulp by extracting hemicellulose and lignin using low-cost ionic liquids. In this study, cellulose pulp was obtained from Miscanthus × giganteus using the protic ionic liquid triethylammonium hydrogen sulfate [N2220][HSO4] with 20% water as a co-solvent and characterised in detail for its material properties as a function of pretreatment severity. We measured the particle size distribution, porosity and crystallinity of the unbleached pulps and the molar weight distribution of the cellulose contained within. We report that the surface area increased and the size of the pulp particles decreased as ionoSolv processing progressed. While the native cellulose I structure was maintained, the average degree of polymerisation of the cellulose was reduced to a DPn of around 300, showing the cellulose polymers are shortened. We correlate the pulp properties with enzymatic saccharification yields, concluding that enzymatic saccharification of the cellulose after ionoSolv pretreatment is mainly enhanced by removing hemicellulose and lignin. We also observed that overtreatment deteriorated saccharification yield and that this coincides with cellulose fibrils becoming coated with pseudolignin redeposited from the ionic liquid solution, as demonstrated by FT-IR spectroscopy. Pseudolignin deposition increases the apparent lignin content, which is likely to increase chemical demand in bleaching, suggesting that both glucose release and material use benefit from a minimum lignin content. Overall, this study demonstrates that cellulose pulps isolated with ionoSolv processing are not only a promising intermediate for high-yield release of purified glucose for biorefining, but also have attractive properties for materials applications that require cellulose I fibrils.
Chambon CL, Fitriyanti V, Verdía P, et al., 2020, Fractionation by sequential antisolvent precipitation of grass, softwood, and hardwood lignins isolated using low-cost ionic liquids and water, ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 3751-3761, ISSN: 2168-0485
In this study, fractionation by sequential antisolvent precipitation was applied to ionoSolv lignins for the first time. Pretreatment with the aqueous low-cost protic ionic liquid N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4], 80 wt % in water) was applied to Miscanthus (herbaceous), willow (hardwood), and pine (softwood) to extract lignin. Then, lignin was sequentially precipitated by the addition of water as an antisolvent. Fractionation appeared to be controlled by the molecular weight of lignin polymers. Fractions isolated with minimal water volumes were shown to have high molecular weight, polydispersity, thermal stability, and Tg (178 °C). Later precipitates were more monodisperse and had high phenolic and total hydroxyl content and lower thermal stability and Tg (136 °C). Addition of 1 g of water per gram of dry IL was able to precipitate up to 90 wt % of lignin. Fractional precipitation represents a novel lignin isolation technique that can be performed as part of the lignin recovery procedure enabling a high degree of control of lignin properties. The effect of the fractionation on lignin structural, chemical, and thermal properties was thoroughly examined by two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance, gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry and compared to the unfractionated lignin precipitate obtained by addition of an excess of water.
Bukowski A, Esau D, Rafat Said AA, et al., 2020, Combining cost‐efficient cellulose and short‐chain carboxylic acid production: the polyoxometalate (POM)‐Ionosolv concept, ChemPlusChem, Vol: 85, Pages: 373-386, ISSN: 2192-6506
Full cost‐effective exploitation of all wood components is key to growing a commercially successful biorefining industry. An innovative process is reported that combines fractionation of lignocellulosic biomass using a low‐cost ionic liquid (Ionosolv) and production of bio‐derived formic acid using polyoxometalates and molecular oxygen (OxFA process). We show that the hemicellulose and part of the lignin were selectively dissolved into the ionic liquid triethylammonium hydrogen sulfate and oxidised in situ to short‐chain, distillable carboxylic acids by a Keggin‐type polyoxometalate with high yields and selectivities. Characterization by several techniques, including ICP‐OES, FTIR, GC, HPLC and NMR spectroscopy confirmed stability of the catalyst over three consecutive POM‐Ionosolv recycles and stable formic acid yields.High formic acid yields of 26 % (pine chips), 23 % (beech chips), and 18 % (Miscanthus ) were obtained with respect to the initial carbon content of the biomass, with unprecedented oxidation selectivities for formic acid of 54–62 % depending on vanadium substitution in the polyoxometalate, the processing temperature and the water content in the reaction mixture.. We also demonstrate that the cellulose rich pulp is a suitable source of glucose via enzymatic saccharification. We report cellulose yields of 37% for Miscanthus (from originally 48% glucan content), 33% for pine (from originally 49%) and 31% for beech (from originally 41%) were achieved, and a saccharification yield of up to 25% without optimisation. With further optimisation, this concept has the potential to generate two chemical products directly from lignocellulose in high yields and selectivities and hence a novel avenue for full utilisation of cellulose, hemicellulose and lignin.
Gschwend F, Chambon C, Biedka M, et al., 2019, Quantitative glucose release from softwood after pretreatment with low-cost ionic liquids, Green Chemistry, Vol: 21, Pages: 692-703, ISSN: 1463-9262
Softwood is an abundantly available feedstock for the bio-based industry, however, achieving cost-effective sugar release is particularly challenging owing to its guaiacyl-only lignin. Here, we report the highly effective pretreatment of the softwood pine (Pinus sylvestris) using ionoSolv pretreatment, a novel ionic liquid-based lignocellulose fractionation technology. Three protic, low-cost ionic liquids, 1-butylimidazolium hydrogen sulfate, triethylammonium hydrogen sulfate and N,N-dimethylbutylammonium hydrogen sulfate, were used to fractionate the biomass into a carbohydrate-rich pulp and a lignin. The carbohydrate-rich pulp was hydrolysed into fermentable sugars by enzymatic saccharification. Under the most successful pretreatment conditions, quantitative glucose release from the pulp was achieved, which equates to a projected glucose release of 464 mg per gram of pine wood entering the process. We further intensified the process by increasing the solid to solvent ratio up to 1:2 g/g while maintaining saccharification yields of 75% of the theoretical maximum. We also demonstrate for the first time that N,N-dimethylbutylammonium hydrogen sulfate, [DMBA][HSO4] is an excellent low-cost pretreatment solvent, surpassing the pretreatment effectiveness of its symmetrically substituted analogue triethylammonium hydrogen sulfate. This shows that ionoSolv pretreatment with protic hydrogen sulfate ionic liquids is a truly feedstock-independent pretreatment option, further increasing the commercial potential of this pretreatment technology.
Chambon C, Mkhize T, Reddy P, et al., 2018, Pretreatment of South African sugarcane bagasse using a low-cost protic ionic liquid: a comparison of whole, depithed, fibrous and pith bagasse fractions, Biotechnology for Biofuels, Vol: 11, ISSN: 1754-6834
BackgroundSugarcane bagasse is an abundant and geographically widespread agro-industrial residue with high carbohydrate content, making it a strong candidate feedstock for the bio-based economy. This study examines the use of the low-cost protic ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) to fractionate a range of South African sugarcane bagasse preparations into a cellulose-rich pulp and lignin. The study seeks to optimize pretreatment conditions and examine the necessity of applying a depithing step on bagasse prior to pretreatment.ResultsPretreatment of five bagasse preparations, namely whole, industrially depithed, laboratory depithed (short and long fiber) and pith bagasse with [TEA][HSO4]:[H2O] (4:1 w/w) solutions produced highly digestible cellulose-rich pulps, as assessed by residual lignin analysis and enzymatic hydrolysis. Pretreatment under the optimized condition of 120 °C for 4 h produced a pretreated cellulose pulp with up to 90% of the lignin removed and enabled the release of up to 69% glucose contained in the bagasse via enzymatic hydrolysis. Glucose yields from whole and depithed bagasse preparations were very similar. Significant differences in lignin recovery were obtained for laboratory depithed bagasse compared with whole and industrially depithed bagasse. The silica-rich ash components of bagasse were seen to partition mainly with the pulp, from where they could be easily recovered in the post-hydrolysis solids.ConclusionsThe five bagasse preparations were compared but did not show substantial differences in composition or cellulose digestibility after pretreatment. Evidence was presented that a depithing step appears to be unnecessary prior to ionoSolv fractionation, potentially affording significant cost and energy savings. Instead, lignin re-deposition onto the pulp surface (and, in turn, particle size and shape) appeared to be major factors affecting the conditioning of bagasse with the applied IL. We show that pith ba
Gschwend FJV, Brandt-Talbot A, Malaret FJ, et al., 2018, Rapid pretreatment of Miscanthus using the low-cost ionic liquid triethylammonium hydrogen sulfate at elevated temperatures, Green Chemistry, Vol: 20, Pages: 3486-3498, ISSN: 1463-9262
Deconstruction with low-cost ionic liquids (ionoSolv) is a promising method to pre-condition lignocellulosic biomass for the production of renewable fuels, materials and chemicals. This study investigated process intensification strategies for the ionoSolv pretreatment of Miscanthus X giganteus using the low-cost ionic liquid triethylammonium hydrogen sulfate ([TEA][HSO4]) in the presence of 20 wt% water, using high temperatures and a high solid to solvent loading of 1:5 g/g. The temperatures investigated were 150, 160, 170 and 180°C. We discuss the effect of pretreatment temperature on lignin and hemicellulose removal, cellulose degradation and enzymatic saccharification yields. We report that very good fractionation can be achieved across all investigated temperatures, including an enzymatic saccharification yield exceeding 75% of the theoretical maximum after only 15 min of treatment at 180°C. We further characterised the recovered lignins which established some tunability of the hydroxyl group content, subunit composition, connectivity and molecular weight distribution in the isolated lignin while maintaining maximum saccharification yield. This drastic reduction of pretreatment time at increased biomass loading without a yield penalty is promising for the development of a commercial ionoSolv pretreatment process.
Hallett J, Fennell P, Gschwend F, et al., 2018, Process for the extraction of metal pollutants from treated cellulosic biomass, CN108291033 (A)
The present invention relates to a process for extracting oxidised metal pollutants from treated cellulosic or lignocellulosic biomass to recover the metal. The treatment also generates a cellulosic or lignocellulosic biomass which can to be used as a feedstock for biofuel, for making cellulose containing materials, and provides a source of other renewable chemicals.
Fogarty RM, Matthews RP, Ashworth CR, et al., 2018, Experimental validation of calculated atomic charges in ionic liquids, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606
A combination of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy has been used to provide an experimental measure of nitrogen atomic charges in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital population analysis, and the atoms in molecules approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of the charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (<0.3 e) should be interpreted with care. We use these validated charges to provide physical insight into nitrogen atomic charges for the ILs probed.
Brandt-Talbot A, Hallett JP, Gschwend FJV, 2018, Ultra-low cost ionic liquids for waste wood biorefining, Pages: 47-54
The BioFlex process is a lignocellulose fractionation process that can treat many different lignocellulosic input materials in a one-size-fits-all system. This now includes low value metal polluted waste wood. We have demonstrated high metal extraction can be achieved with ultra-low cost BioFlex ILs. The ionic liquid solution based on 1-methylimidazolium chloride was shown to be particularly effectively in removing heavy metals from waste wood while affording a cellulose pulp that results in high glucose yields after enzymatic saccharification. It has further been shown that copper can be deposited from BioFlex ionic liquids. The presence of biomass degradation products from pretreatment did not alter the deposition behaviour. Ionic liquid based pretreatment therefore represents a promising platform for the decontamination of metal contaminated waste wood while concomitantly producing intermediate fractions that can be used for biorefining. Our techno-economic estimate shows that the BioFlex process with metal polluted waste wood is economically attractive at a small commercial scale. The next focus is finding suitable applications for the BioFlex process outputs.
Fogarty RM, Matthews RP, Clough MT, et al., 2017, NEXAFS spectroscopy of ionic liquids: experiments versus calculations, Physical Chemistry Chemical Physics, Vol: 19, Pages: 31156-31167, ISSN: 1463-9076
Experimental near edge X-ray absorption fine structure (NEXAFS) spectra are reported for 12 ionic liquids (ILs) encompassing a range of chemical structures for both the sulfur 1s and nitrogen 1s edges and compared with time-dependent density functional theory (TD-DFT) calculations. The energy scales for the experimental data were carefully calibrated against literature data. Gas phase calculations were performed on lone ions, ion pairs and ion pair dimers, with a wide range of ion pair conformers considered. For the first time, it is demonstrated that TD-DFT is a suitable method for simulating NEXAFS spectra of ILs, although the number of ions included in the calculations and their conformations are important considerations. For most of the ILs studied, calculations on lone ions in the gas phase were sufficient to successfully reproduce the experimental NEXAFS spectra. However, for certain ILs – for example, those containing a protic ammonium cation – calculations on ion pairs were required to obtain a good agreement with experimental spectra. Furthermore, significant conformational dependence was observed for the protic ammonium ILs, providing insight into the predominant liquid phase cation–anion interactions. Among the 12 investigated ILs, we find that four have an excited state that is delocalised across both the cation and the anion, which has implications for any process that depends on the excited state, for example, radiolysis. Considering the collective experimental and theoretical data, we recommend that ion pairs should be the minimum number of ions used for the calculation of NEXAFS spectra of ILs.
Brandt-Talbot A, Weigand L, 2017, Highlights from the Faraday Discussion: Bio-resources: Feeding a Sustainable Chemical Industry, 19-21 June 2017, London, UK, Chemical Communications, Vol: 53, Pages: 12848-12856, ISSN: 1359-7345
Hallett J, Welton T, Brandt-Talbot A, 2017, Treatment, EP3244371 (A1)
The present disclosure relates to an improved method for treating a lignocellulose biomass in order to dissolve the lignin therein, while the cellulose does not dissolve. The cellulose pulp obtained can be used to produce glucose. In addition the lignin can be isolated for subsequent use in the renewable chemical industry.
Gschwend FJV, Brandt-Talbot A, Chambon CL, et al., 2017, Ultra-Low Cost Ionic Liquids for the Delignification of Biomass, Ionic Liquids: Current State and Future Directions, Editors: Shiflett, Scurto, Publisher: American Chemical Society, Pages: 209-223, ISBN: 9780841232136
Low-cost pretreatment of lignocellulosic biomass is an essential next step toward large-scale deployment as renewable liquid fuels, materials or chemicals. Ionic liquids (ILs) are highly effective at pretreatment, but high IL cost has hindered commercial viability. We have recently developed low-cost (ca. $1/kg) ILs, such as triethylammonium hydrogen sulphate, for pretreatment. In this chapter we discuss the fractionation of the grass Miscanthus x giganteus, wherein we deconstruct the lignocellulosic matrix into a cellulose-rich pulp, a recovered lignin fraction and an organic distillate. More than 80% of the lignin and quantitative hemicelluloses are removed during extraction. This results in 70-90% glucose release during enzymatic saccharification. The IL can also be successfully recovered and reused, with >99% IL recovery and minimal effects on efficiency of extraction. A detailed mass balance of all components and subsequent economic analysis revealed this efficient pretreatment with an ultra-low cost IL could result in an economically viable pretreatment process.
Argyropoulos D, Bitter H, Brandt-Talbot A, et al., 2017, Conversion technologies: general discussion, FARADAY DISCUSSIONS, Vol: 202, Pages: 371-389, ISSN: 1359-6640
Fogarty RM, Rowe R, Matthews RP, et al., 2017, Atomic charges of sulfur in ionic liquids: experiments and calculations, Faraday Discussions, Vol: 206, Pages: 183-201, ISSN: 1359-6640
Experimental near edge X-ray absorption fine structure (NEXAFS) spectra, X-ray photoelectron (XP) spectra and Auger electron spectra are reported for sulfur in ionic liquids (ILs) with a range of chemical structures. These values provide experimental measures of the atomic charge in each IL and enable the evaluation of the suitability of NEXAFS spectroscopy and XPS for probing the relative atomic charge of sulfur. In addition, we use Auger electron spectroscopy to show that when XPS binding energies differ by less than 0.5 eV, conclusions on atomic charge should be treated with caution. Our experimental data provides a benchmark for calculations of the atomic charge of sulfur obtained using different methods. Atomic charges were computed for lone ions and ion pairs, both in the gas phase (GP) and in a solvation model (SMD), with a wide range of ion pair conformers considered. Three methods were used to compute the atomic charges: charges from the electrostatic potential using a grid based method (ChelpG), natural bond orbital (NBO) population analysis and Bader’s atoms in molecules (AIM) approach. By comparing the experimental and calculated measures of the atomic charge of sulfur, we provide an order for the sulfur atoms, ranging from the most negative to the most positive atomic charge. Furthermore, we show that both ChelpG and NBO are reasonable methods for calculating the atomic charge of sulfur in ILs, based on the agreement with both the XPS and NEXAFS spectroscopy results. However, the atomic charges of sulfur derived from ChelpG are found to display significant, non-physical conformational dependence. Only small differences in individual atomic charge of sulfur were observed between lone ion (GP) and ion pair IL(SMD) model systems, indicating that ion–ion interactions do not strongly influence individual atomic charges.
Fennell PS, hallett J, Brandt-Talbot A, et al., 2017, An economically viable ionic liquid for the fractionation of lignocellulosic biomass, RSC Green Chemistry, Vol: 19, Pages: 3078-3102, ISSN: 1757-7047
Cost-effective fractionation (pretreatment) of lignocellulosic biomass is necessary to enable its large-scale use as a source of liquid fuels, bio-based materials and bio-derived chemicals. While a number of ionic liquids (ILs) have proven capable of highly effective pretreatment, their high cost presents a barrier to commercial viability. In this study, we investigate in detail the application of the low-cost (ca. $1 kg−1) ionic liquid triethylammonium hydrogen sulfate for the fractionation of the grass Miscanthus x giganteus into a cellulose rich pulp, a lignin and a distillate. We found that up to 85% of the lignin and up to 100% of the hemicellulose were solubilized into the IL solution. The hemicellulose dissolved mainly in monomeric form, and pentoses were partially converted into furfural. Up to 77% of the glucose contained in the biomass could be released by enzymatic saccharification of the pulp. The IL was successfully recovered and reused four times. A 99% IL recovery was achieved each time. Effective lignin removal and high saccharification yields were maintained during recycling, representing the first demonstration that repeated IL use is feasible due to the self-cleaning properties of the non-distillable solvent. We further demonstrate that furfural and acetic acid can be separated quantitatively from the non-volatile IL by simple distillation, providing an easily recoverable, valuable co-product stream, while IL degradation products were not detected. We further include detailed mass balances for glucose, hemicellulose and lignin, and a preliminary techno-economic estimate for the fractionation process. This is the first demonstration of an efficient and repeated lignocellulose fractionation with a truly low-cost IL, and opens a path to an economically viable IL-based pretreatment process.
Weigand L, Mostame S, Brandt-Talbot A, et al., 2017, Effect of pretreatment severity on the cellulose and lignin isolated from Salix using ionoSolv pretreatment, Faraday Discussions, Vol: 202, Pages: 331-349, ISSN: 1359-6640
The ionoSolv pretreatment is a new technique employing protic low-cost ionic liquids and has previously been applied to successfully fractionate switchgrass and the grass Miscanthus giganteus. This study investigates the effect of using the protic ionic liquid solution [N2220][HSO4]80% with two different acid/base ratios (1.02 and 0.98) at 120, 150 and 170 °C on the pretreatment outcome of the hardwood willow. The ionic liquid solution was able to fractionate willow, and a pulp and lignin fraction were recovered after treatment. The pretreatment success was determined via enzymatic hydrolysis of the pulp, which showed that the ionoSolv pretreatment was able to increase enzymatic glucose yields compared to untreated willow biomass. The pretreatment produced a cellulose-rich pulp with high hemicellulose and lignin removal. The pulp composition and glucose yield after saccharification were greatly influenced by the acidity of the ionic liquid solution, temperature and pretreatment time. The extracted lignin was analysed via 2-D HSQC NMR spectroscopy and GPC to investigate the changes in the lignin structure induced by the pretreatment severity. The lignin structure (in terms of inter-unit linkages and S/G ratio) and molecular weight varied significantly depending on the pretreatment conditions used.
Clarke CJ, Tu WC, Weigand L, et al., 2017, Solvation behavior of ionic liquids and their role in the production of lignocellulosic biofuels and sustainable chemical feedstocks, Advanced Green Chemistry: Part 1: Greener Organic Reactions and Processes, Pages: 77-134, ISBN: 9789813228108
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De Gregorio GF, Weber CC, Gräsvik J, et al., 2016, Mechanistic insights into lignin depolymerisation in acidic ionic liquids, Green Chemistry, Vol: 18, Pages: 5456-5465, ISSN: 1744-1560
Acidic anions of ionic liquids have been demonstrated as efficient catalysts for the cleavage of the β-O-4 ether linkage prevalent in the lignin superstructure. Through the use of lignin model compounds with varying functionality and by monitoring reaction kinetics, a full mechanistic investigation into the hydrolysis of the β-O-4 linkage in acidic ionic liquid solutions is reported. Hammett acidities are reported for different 1-butyl-3-methylimidazolium hydrogen sulfate [C4C1im][HSO4] ionic liquid systems with varying acid and water concentrations and were correlated to substrate reactivity. Results show that the rate of ether cleavage increases with an increase in acidity and the initial dehydration of the model compound is the rate-determining step of the reaction. The Eyring activation parameters of the reaction in hydrogen sulfate ionic liquids with a variety of cations are reported, indicating a consistent E1 dehydration mechanism. Hydrogen bonding in protic ionic liquids was shown to significantly influence anion–cation interactions, consequently altering the solvation of the protonated starting material and therefore the overall rate of reaction. Comparison of reaction rates in these ionic liquids with results within aqueous or aqueous/organic media indicate that the ionic liquids facilitate more rapid cleavage of the β-O-4 ether linkage even under less acidic conditions. All the reported results give a complete overview of both the mechanistic and solvation effects of acidic ionic liquids on lignin model compounds and provide scope for the appropriate selection and design of ionic liquids for lignin processing.
Eminov S, Filippousi P, Brandt A, et al., 2016, Direct catalytic conversion of cellulose to 5-hydroxymethylfurfural using ionic liquids, Inorganics, Vol: 4, ISSN: 2304-6740
Cellulose is the single largest component of lignocellulosic biomass and is an attractive feedstock for a wide variety of renewable platform chemicals and biofuels, providing an alternative to petrochemicals and petrofuels. This potential is currently limited by the existing methods of transforming this poorly soluble polymer into useful chemical building blocks, such as 5-hydroxymethylfurfural (HMF). Ionic liquids have been used successfully to separate cellulose from the other components of lignocellulosic biomass and so the use of the same medium for the challenging transformation of cellulose into HMF would be highly attractive for the development of the biorefinery concept. In this report, ionic liquids based on 1-butyl-3-methylimidazolium cations [C4C1im]+ with Lewis basic (X = Cl−) and Brønsted acidic (X = HSO4−) anions were used to investigate the direct catalytic transformation of cellulose to HMF. Variables probed included the composition of the ionic liquid medium, the metal catalyst, and the reaction conditions (temperature, substrate concentration). Lowering the cellulose loading and optimising the temperature achieved a 58% HMF yield after only one hour at 150 °C using a 7 mol % loading of the CrCl3 catalyst. This compares favourably with current literature procedures requiring much longer reactions times or approaches that are difficult to scale such as microwave irradiation.
Eminov S, Brandt A, Wilton-Ely JD, et al., 2016, The Highly Selective and Near-Quantitative Conversion of Glucose to 5-Hydroxymethylfurfural Using Ionic Liquids, PLOS One, Vol: 11, ISSN: 1932-6203
A number of ionic liquids have been shown to be excellent solvents for lignocellulosic biomass processing, and some of these are particularly effective in the production of the versatile chemical building block 5-hydroxymethylfurfural (HMF). In this study, the production of HMF from the simple sugar glucose in ionic liquid media is discussed. Several aspects of the selective catalytic formation of HMF from glucose have been elucidated using metal halide salts in two distinct ionic liquids, 1-butyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium hydrogen sulfate as well as mixtures of these, revealing key features for accelerating the desired reaction and suppressing byproduct formation. The choice of ionic liquid anion is revealed to be of particular importance, with low HMF yields in the case of hydrogen sulfate-based salts, which are reported to be effective for HMF production from fructose. The most successful system investigated in this study led to almost quantitative conversion of glucose to HMF (90% in only 30 minutes using 7 mol% catalyst loading at 120°C) in a system which is selective for the desired product, has low energy intensity and is environmentally benign.
Gschwend FJ, Brandt A, Chambon CL, et al., 2016, Pretreatment of Lignocellulosic Biomass with Low-cost Ionic Liquids., Jove-Journal of Visualized Experiments, Vol: 114, ISSN: 1940-087X
A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of a variety of lignocellulosic feedstocks. Here we demonstrate the use of these low-cost protic ILs in the deconstruction of lignocellulosic biomass (Ionosolv pretreatment), yielding cellulose and a purified lignin. In the most generic process, the protic ionic liquid is synthesized by accurate combination of aqueous acid and amine base. The water content is adjusted subsequently. For the delignification, the biomass is placed into a vessel with IL solution at elevated temperatures to dissolve the lignin and hemicellulose, leaving a cellulose-rich pulp ready for saccharification (hydrolysis to fermentable sugars). The lignin is later precipitated from the IL by the addition of water and recovered as a solid. The removal of the added water regenerates the ionic liquid, which can be reused multiple times. This protocol is useful to investigate the significant potential of protic ILs for use in commercial biomass pretreatment/lignin fractionation for producing biofuels or renewable chemicals and materials.
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