Imperial College London

Prof Jason P. Hallett

Faculty of EngineeringDepartment of Chemical Engineering

Professor of Sustainable Chemical Technology
 
 
 
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Contact

 

+44 (0)20 7594 5388j.hallett Website

 
 
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Location

 

228bBone BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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184 results found

Shmool TA, Martin LK, Clarke CJ, Bui-Le L, Polizzi KM, Hallett JPet al., 2021, Exploring conformational preferences of proteins: ionic liquid effects on the energy landscape of avidin, Chemical Science, Vol: 12, Pages: 196-209, ISSN: 2041-6520

© 2021 The Royal Society of Chemistry. In this work we experimentally investigate solvent and temperature induced conformational transitions of proteins and examine the role of ion-protein interactions in determining the conformational preferences of avidin, a homotetrameric glycoprotein, in choline-based ionic liquid (IL) solutions. Avidin was modified by surface cationisation and the addition of anionic surfactants, and the structural, thermal, and conformational stabilities of native and modified avidin were examined using dynamic light scattering, differential scanning calorimetry, and thermogravimetric analysis experiments. The protein-surfactant nanoconjugates showed higher thermostability behaviour compared to unmodified avidin, demonstrating distinct conformational ensembles. Small-angle X-ray scattering data showed that with increasing IL concentration, avidin became more compact, interpreted in the context of molecular confinement. To experimentally determine the detailed effects of IL on the energy landscape of avidin, differential scanning fluorimetry and variable temperature circular dichroism spectroscopy were performed. We show that different IL solutions can influence avidin conformation and thermal stability, and we provide insight into the effects of ILs on the folding pathways and thermodynamics of proteins. To further study the effects of ILs on avidin binding and correlate thermostability with conformational heterogeneity, we conducted a binding study. We found the ILs examined inhibited ligand binding in native avidin while enhancing binding in the modified protein, indicating ILs can influence the conformational stability of the distinct proteins differently. Significantly, this work presents a systematic strategy to explore protein conformational space and experimentally detect and characterise 'invisible' rare conformations using ILs.

Journal article

Cuéllar-Franca RM, García-Gutiérrez P, Hallett JP, Mac Dowell Net al., 2021, A life cycle approach to solvent design: challenges and opportunities for ionic liquids – application to CO2 capture, Reaction Chemistry & Engineering

<p>CO<sub>2</sub> capture and storage is widely anticipated to play a key role in combatting climate change, however the solvents proposed for use have embedded environmental concerns.</p>

Journal article

Bhatia R, Lad JB, Bosch M, Bryant DN, Leak D, Hallett JP, Franco TT, Gallagher JAet al., 2020, Production of oligosaccharides and biofuels from Miscanthus using combinatorial steam explosion and ionic liquid pretreatment., Bioresour Technol, Vol: 323

Pretreatment strategies are fundamental to effectively deconstruct lignocellulosic biomass and economically produce biofuels, biomaterials and bio-based chemicals. This study evaluated individual and combinatorial steam explosion (SE) and ionic liquid (IL) pretreatments for production of high-value oligosaccharides from a novel seed-based Miscanthus hybrid (Mx2779). The two ILs used for pretreatment were triethylammonium hydrogen sulphate [TEA][HSO4] and 1-ethyl-3-methylimidazolium acetate [C2mim][OAc]. The results showed that each pretreatment leads to distinct effects on the fragmentation (cellulose and xylan dissolution, delignification, deacetylation) and physicochemical modification (cellulose and lignin properties) of lignocellulose. This, in turn, dictated enzymatic hydrolysis efficiencies of the cellulose pulp to glucose or gluco-oligosaccharides for downstream applications. Our findings suggest that the stand-alone SE or [C2mim][OAc] pretreatments may offer cost advantages over [TEA][HSO4] through the production of oligosaccharides such as xylo- and gluco-oligosaccharides. This study also highlights technical and economic pretreatment process challenges related to the production of oligosaccharides from Miscanthus Mx2779 biomass.

Journal article

Clarke CJ, Richardson ND, Firth AEJ, Hallett JP, Licence Pet al., 2020, Thermolysis of Organofluoroborate Ionic Liquids to NHC-Organofluoroborates, ACS Sustainable Chemistry and Engineering, Vol: 8, Pages: 16386-16390

© 2020 American Chemical Society. A range of dialkylimidazolium organotrifluoroborate ionic liquids were prepared by anion metathesis from newly available potassium organotrifluoroborate salts, and their physical properties were characterized by TGA, DSC, and STA. Thermal decomposition was subsequently investigated under vacuum with direct insertion mass spectrometry to determine whether thermolysis was a viable route to prepare N-heterocyclic carbene organofluoroborates, which are an important class of emerging compounds. Several key targets were identified, which highlighted the potential to shortcut complex synthetic methodologies otherwise required to access such molecules.

Journal article

Bui-Le L, Brogan APS, Hallett JP, 2020, Solvent-free liquid avidin as a step toward cold chain elimination, BIOTECHNOLOGY AND BIOENGINEERING, ISSN: 0006-3592

Journal article

Skoronski E, Fernandes M, Malaret FJ, Hallett JPet al., 2020, Use of phosphonium ionic liquids for highly efficient extraction of phenolic compounds from water, Separation and Purification Technology, Vol: 248, Pages: 1-8, ISSN: 1383-5866

Ionic liquids (ILs) are undergoing development as extractants for phenolic compounds from wastewater due to their outstanding properties. Although many ILs have been considered, the use of phosphonium-based ILs has thus far been neglected, despite advantages in viscosity and low water solubility. This work details the application of phosphonium-based ILs for the liquid–liquid extraction of phenolic compounds from water. The selected target contaminants, phenol and 2,4-dichlorophenol, were extracted using two ILs composed of trihexyltetradecylphosphonium cations with decanoate or bis(2,4,4-trymetylpentyl)phosphinate anions. The effect of volume ratio, time of contact, pH, temperature and (inorganic) salt concentration on the extraction efficiency were examined. Additionally, the ILs used in this study were characterised in terms of water solubility and solvatochromic polarity. These ILs are less soluble in water than the others reported in the literature, and even at a volume ratio (water: ionic liquid) of 135, the IL can extract more than 99% and 89% of 2,4-dichlorophenol and phenol, respectively, in just 10 min, with the best extraction performance at lower temperatures and pH lower than the pKa of these phenolic compounds. Overall, these ILs demonstrate high potential for phenol extraction and can be considered as a powerful alternative for wastewater treatment.

Journal article

Abouelela AR, Tan S-Y, Kelsall GH, Hallett JPet al., 2020, Toward a Circular Economy: Decontamination and Valorization of Postconsumer Waste Wood Using the ionoSolv Process, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 14441-14461, ISSN: 2168-0485

Journal article

Green SP, Wheelhouse KM, Payne AD, Hallett JP, Miller PW, Bull JAet al., 2020, On the Use of Differential Scanning Calorimetry for Thermal Hazard Assessment of New Chemistry: Avoiding Explosive Mistakes, Angewandte Chemie, Vol: 132, Pages: 15930-15934, ISSN: 0044-8249

© 2020 Wiley-VCH GmbH Differential scanning calorimetry (DSC) is increasingly used as evidence to support a favourable safety profile of novel chemistry, or to highlight the need for caution. DSC enables preliminary assessment of the thermal hazards of a potentially energetic compound. However, unlike other standard characterisation methods, which have well defined formats for reporting data, the current reporting of DSC results for thermal hazard assessment has shown concerning trends. Around half of all results in 2019 did not include experimental details required to replicate the procedure. Furthermore, analysis for thermal hazard assessment is often only conducted in unsealed crucibles, which could lead to misleading results and dangerously incorrect conclusions. We highlight the specific issues with DSC analysis of hazardous compounds currently in the organic chemistry literature and provide simple “best practice” guidelines which will give chemists confidence in reported DSC results and the conclusions drawn from them.

Journal article

Green S, Wheelhouse K, Payne A, Hallett J, Miller P, Bull Jet al., 2020, On the use of differential scanning calorimetry for thermal hazard assessment of new chemistry: Avoiding explosive mistakes, Angewandte Chemie International Edition, Vol: 59, Pages: 15798-15802, ISSN: 1433-7851

Differential scanning calorimetry (DSC) is increasingly used as evidence to support a favourable safety profile of novel chemistry, or to highlight the need for caution. DSC enables preliminary assessment of the thermal hazards of a potentially energetic compound. However, unlike other standard characterisation methods, which have well defined formats for reporting data, the current reporting of DSC results for thermal hazard assessment has shown concerning trends. Around half of all results in 2019 did not include experimental details required to replicate the procedure. Furthermore, analysis for thermal hazard assessment is often only conducted in unsealed crucibles, which could lead to misleading results and dangerously incorrect conclusions. We highlight the specific issues with DSC analysis of hazardous compounds currently in the organic chemistry literature and provide simple ‘best practice’ guidelines which will give chemists confidence in reported DSC results and the conclusions drawn from them.

Journal article

Tan S-Y, Hallett J, Geoff K, 2020, Electrodeposition of lead from methanesulfonic acid and methanesulfonate ionic liquid derivatives, Electrochimica Acta, Vol: 353, Pages: 1-11, ISSN: 0013-4686

The influence is reported of electrolyte composition on the electrochemistry of PbII and electrodeposition morphology of Pb in aqueous methanesulfonic acid (MSA) and two methanesulfonate-based ionic liquids: 1-butyl-3-methylimidazolium methanesulfonate and N,N-dimethylbutylammonium methanesulfonate. Cyclic voltammetry and chronoamperometry indicated that the reduction of PbII ions to Pb was a diffusion-controlled process proceeding via a two-electron transfer process at -0.67 V vs. Ag (1 M MSA) and involved 3-D progressive nucleation. Scanning electron microscopy showed a strong influence of deposition potential and electrolyte composition on the morphology of Pb deposits. Experimental data was used to model predictions of the specific electrical energy consumption for cathodic PbII electrodeposition coupled with either anodic oxygen evolution or PbO2 electrodeposition.

Journal article

Chen M, Malaret F, Firth AEJ, Verdia P, Abouelela AR, Chen Y, Hallett JPet al., 2020, Design of a combined ionosolv-organosolv biomass fractionation process for biofuel production and high value-added lignin valorisation, GREEN CHEMISTRY, Vol: 22, Pages: 5161-5178, ISSN: 1463-9262

Journal article

Gschwend FJ, Hennequin LM, Brandt-Talbot A, Bedoya-Lora F, Kelsall GH, Polizzi K, Fennell PS, Hallett JPet 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.

Journal article

Firth AEJ, Mac Dowell N, Fennell PS, Hallett JPet al., 2020, Assessing the economic viability of wetland remediation of wastewater, and the potential for parallel biomass valorisation, Environmental Science: Water Research & Technology, Vol: 6, Pages: 2103-2121, ISSN: 2053-1400

Constructed wetlands have been shown to consistently remove a wide range of pollutants from contaminated water. However, no wide-ranging studies exist on the economic viability of this technology. This paper performs a high-level economic comparison between wetland remediation and conventional water remediation technologies, for a wide range of contaminant inputs, outputs, and flow rates. The cases considered are nutrient removal from wastewater, and remediation of low-pH and circumneutral acid mine drainage (AMD). The first-order P-k-C* model is used for nutrient removal, while a zeroth-order model is used for AMD remediation, with removal rate data taken from the literature. The number of wetland cells employed was found to significantly affect the overall cost of nutrient removal, allowing savings of up to 86% and 42% for biochemical oxygen demand and phosphorus removal, particularly for low concentrations and flow rates. For integrated secondary and tertiary treatment, wetland remediation was economically competitive down to stringent effluent standards. A sensitivity analysis was performed on sizing and costing parameters of nutrient removal wetlands, with required wetland size found to be most strongly correlated with the assumed removal rate, and land costs found to have relatively little effect on overall costs. Wetland remediation of AMD was only found to be economically favourable for less severe conditions and lower flow rates when treating low-pH drainage, and was heavily influenced by the acidity removal rate. However, the majority of site data from literature was found to fall within this range of conditions. For circumneutral AMD, wetland remediation was found to be cheaper for all simulated cases. The feasibility of offsetting wetland remediation costs through biomass valorisation was investigated for a range of products, with area requirements for minimum economic production identified as the principal barrier.

Journal article

Clarke CJ, Bui-Le L, Corbett PJ, Hallett JPet al., 2020, Implications for heavy metal extractions from hyper saline brines with [NTf2](-) ionic liquids: performance, solubility, and cost, Industrial and Engineering Chemistry Research, Vol: 59, Pages: 12536-12544, ISSN: 0888-5885

The bis(trifluoromethanesulfonyl)imide anion, [NTf2]−, can be paired with organic cations to give hydrophobic ionic liquids (ILs) that form secondary phases with water. These ILs are often identified as green solvents and considered as replacements for traditional organic solvents in chemical processes, i.e., aqueous biphasic extractions. Here, we consider a range of hydrophobic [NTf2]− ILs as extraction phases with hypersaline brines for heavy metal remediation. Extraction experiments were complicated by the partial solubility of the hydrophobic ILs, and ion chromatography was used to quantify the anion and cation losses to the aqueous phase. Although IL leaching was lower in hypersaline brine than in water (i.e., salting-out), IL losses were significant at relatively low volume ratios (Vaq/VIL) for short-chain and functional ILs. IL purity was also affected by cation exchange; more organic cations were lost to the aqueous phase than [NTf2]− anions. Solvent replenishment costs were extremely high due to loss to the aqueous phase and high IL prices. New separation technologies will be required if these ILs are to be used industrially; recovery is unlikely to offset the cost with current separation methodologies.

Journal article

Chambon CL, Karia T, Sandwell P, Hallett JPet al., 2020, Techno-economic assessment of biomass gasification-based mini-grids for productive energy applications: The case of rural India, Renewable Energy, Vol: 154, Pages: 432-444, ISSN: 0960-1481

As the costs of solar PV continuously decrease and pollution legislation imposes less burning of agricultural residues, decentralized renewable energy is increasingly affordable for providing electricity to one billion people lacking access to a power grid. This paper presents a techno-economic feasibility case study of biomass gasification in off-grid and grid-connected mini-grids for community-scale energy application in rural Uttar Pradesh, India. Energy demand data was collected through surveys in a village with irrigation and agro-processing loads and off-grid households and used to construct a seasonal load profile based on statistical methods. This was used to simulate single-source and hybrid mini-grids based on solar PV, biomass gasification and diesel generation using HOMER Pro. Hybrid PV-biomass or PV-diesel systems were found to offer the highest reliability for off-grid power at the lowest cost. Single-source PV was cheaper than biomass gasification, though the cost of electricity is highly sensitive to biomass supply and gasifier maintenance. Both renewable options were around half the cost of diesel generation. The findings held across grid-connected systems with weak, moderate and strong reliability of grid supply. This suggests that biomass gasification-based mini-grids are not cost-competitive with PV unless the two generation sources are combined in a hybrid system, though they require operational testing prior to implementation.

Journal article

Clarke CJ, Bui-Le L, Hallett JP, Licence Pet al., 2020, Thermally-Stable Imidazolium Dicationic Ionic Liquids with Pyridine Functional Groups, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 8, Pages: 8762-8772, ISSN: 2168-0485

Journal article

Nakasu PYS, Clarke CJ, Rabelo SC, Costa AC, Brandt-Talbot A, Hallett JPet al., 2020, Interplay of acid-base ratio and recycling on the pretreatment performance of the protic ionic liquid monoethanolammonium acetate, ACS Sustainable Chemistry and Engineering, Vol: 8, Pages: 7952-7961, ISSN: 2168-0485

The use of protic ammonium ionic liquids (PILs) in the pretreatment of lignocellulosic biomass is a promising alternative to using expensive aprotic ionic liquids such as 1-ethyl-3-methylimidazolium acetate, [Emim][OAc]. In this work, the PIL monoethanolammonium acetate, [MEA][OAc], was used for the pretreatment of sugar cane bagasse. The study investigated changing the acid base ratio (ABR) from 0.1 to 10 and recycling of the solvent. We determined the lignin extraction, lignin recovery, solvent recovery, and enzymatic saccharification yield and compared the performance to that of the pure amine base, monoethanolamine. We found that lignin extraction and glucose release during enzymatic saccharification increased with base (amine) content, reaching up to 84% and 96%, respectively, after 72 h of saccharification for the 0.1 ABR. Up to 97% of the solvent was recovered for the 1.0 ABR. A higher acid content led to increased hemicellulose extraction into the liquid phase and reduced ionic liquid recovery. A partial conversion of the PIL into N-(hydroxyethyl) acetamide was observed after pretreatment, with up to 86% of conversion after the sixth use for the 1.0 ABR. A negative correlation (R2 = 0.96) was found between the acetamide content in the solvent and the saccharification yield. The drop in pretreatment performance was also correlated with a decrease in accumulated lignin recovery and the molecular weight of the isolated lignins. Acetamide formation was reduced when excess base was present. Recycling of the mixture with 0.5 ABR showed that the performance was unchanged (97% saccharification yield) after three uses, although 28% of the mixture was converted into the acetamide. The study shows that protic acetate ILs made from primary amines form an equilibrium with their amide and a low ABR is required in order to maintain high pretreatment efficiency when the PIL is reused.

Journal article

Baqeel H, Diaz I, Tulus V, Chachuat B, Guillén-Gosálbez G, Hallett Jet al., 2020, Role of life-cycle externalities in the valuation of protic ionic liquids – a case study in biomass pretreatment solvents, Green Chemistry, Vol: 22, Pages: 3132-3140, ISSN: 1463-9262

Ionic liquids have found their way into many applications where they show a high potential to replace traditional chemicals. But there are concerns over their ecological impacts (toxicity and biodegradability) and high cost, which have limited their use so far. The outcome of existing techno-economic and life-cycle assessments comparing ionic liquids with existing solvents has proven hard to interpret due to the many metrics used and trade-offs between them. For the first time, this paper couples the concept of monetization with detailed process simulation and life-cycle assessment to estimate the true cost of ionic liquids. A comparative case study on four solvents used in lignocellulosic biomass pretreatment is conducted: triethylammonium hydrogen sulfate [TEA][HSO4], 1-methylimidazolium hydrogen sulfate [HMIM][HSO4], acetone from fossil sources, and glycerol from renewable sources. The results show that the total monetized cost of production accounting for externalities can be more than double the direct costs estimated using conventional economic assessment methods. The ionic liquid [TEA][HSO4] is found to have the lowest total cost, while the renewable solvent glycerol presents the highest total cost. We expect this methodology to provide a starting point for future research and development in sustainable ionic liquids

Journal article

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.

Journal article

Clarke C, Bui-Le L, Hallett J, 2020, Ion chromatography for monitoring [NTf2]- anion contaminants in pure and saline water, Analytical Methods, Vol: 12, Pages: 2244-2252, ISSN: 1759-9660

Hydrophobic ionic liquid containing bis(trifluoromethanesulfonyl)imide, [NTf2]-, anions partially dissolve in aqueous phases. The potential ecotoxicity of [NTf2]- means wastewater streams must be closely monitored to avoid environmental release. A new anion chromatography method is presented, which improves on existing techniques and methods by significantly decreasing analysis time and improving chromatographic peak properties. Subsequently, the limit of detection was lowered to 5 µM (1.4 ppm) and limit of quantification lowered to 30 μM (8.5 ppm), without the use of expensive concentrator columns or mass spectrometers. The chromatographic method employed a Dionex AS20 column designed for trace analysis of perchlorate in drinking water, which is ideal for highly polarizable [NTf2]- ions to be detected with high accuracy in the presence of high salinity samples, such as seawater. The technique is consequently ideal for environmental monitoring or process design of [NTf2]- ionic liquid-based applications.

Journal article

Bui-Le L, Clarke CJ, Bröhl A, Brogan APS, Arpino JAJ, Polizzi KM, Hallett Jet al., 2020, Revealing the complexity of ionic liquid-protein interactions through a multi-technique investigation, Communications Chemistry, Vol: 3, ISSN: 2399-3669

Ionic liquids offer exciting possibilities for biocatalysis as solvent properties provide rare opportunities for customizable, energy-efficient bioprocessing. Unfortunately, proteins and enzymes are generally unstable in ionic liquids and several attempts have been made to explain why; however, a comprehensive understanding of the ionic liquid–protein interactions remains elusive. Here, we present an analytical framework (circular dichroism (CD), fluorescence, ultraviolet-visible (UV/Vis) and nuclear magnetic resonance (NMR) spectroscopies, and small-angle X-ray scattering (SAXS)) to probe the interactions, structure, and stability of a model protein (green fluorescent protein (GFP)) in a range (acetate, chloride, triflate) of pyrrolidinium and imidazolium salts. We demonstrate that measuring protein stability requires a similar holistic analytical framework, as opposed to single-technique assessments that provide misleading conclusions. We reveal information on site-specific ionic liquid–protein interactions, revealing that triflate (the least interacting anion) induces a contraction in the protein size that reduces the barrier to unfolding. Robust frameworks such as this are critical to advancing non-aqueous biocatalysis and avoiding pitfalls associated with single-technique investigations.

Journal article

Tu W-C, Weigand L, Hummel M, Sixta H, Brandt-Talbot A, Hallett JPet 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.

Journal article

Malaret F, Gschwend FJV, Lopes JM, Tu WC, Hallett Jet al., 2020, Eucalyptus Red Grandis pretreatment with protic ionic liquids: effect of severity and influence of sub/super-critical CO2 atmosphere on pretreatment performance, RSC Advances: an international journal to further the chemical sciences, Vol: 10, Pages: 16050-16060, ISSN: 2046-2069

Deconstruction of lignocellulosic biomass with low-cost ionic liquids (ILs) has proven to be a promising technology that could be implemented in a biorefinery to obtain renewable materials, fuels and chemicals. This study investigates the pretreatment efficacy of the ionoSolv pretreatment of Eucalyptus red grandis using the low-cost ionic liquid triethylammonium hydrogen sulfate ([N2220][HSO4]) in the presence of 20 wt% water at 10% solids loading. The temperatures investigated were 120 °C and 150 °C. Also, the influence of performing the pretreatment under sub-critical and supercritical CO2 was investigated. The IL used is very effective in deconstructing eucalyptus, producing cellulose-rich pulps resulting in enzymatic saccharification yields of 86% for some pretreatment conditions. It has been found that under a CO2 atmosphere, the ionoSolv process is pressure independent. The good performance of this IL in the pretreatment of eucalyptus is promising for the development of a large-scale ionoSolv pretreatment processes.

Journal article

Chambon CL, Fitriyanti V, Verdía P, Yang SM, Hérou S, Titirici M-M, Brandt-Talbot A, Fennell PS, Hallett JPet 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.

Journal article

Brogan APS, Clarke CJ, Charalambidou A, Loynachan CN, Norman SE, Doutch J, Hallett JPet al., 2020, Expanding the design space of gel materials through ionic liquid mediated mechanical and structural tuneability, Materials Horizons, Vol: 7, Pages: 820-826, ISSN: 2051-6355

Ionogels are an emerging class of soft material with exceptional properties stemming from high ionic liquid content. In contrast to other gel systems, the ionic liquid component provides an extra level of design. However, this highly modular nature has yet to be fully explored and the role ionic liquids play in the structural properties of gel-based materials is poorly understood. Here, methodical small angle neutron scattering and X-ray photoelectron spectroscopy studies reveal the relationship between bulk structure and surface composition of a soft material for the first time. Furthermore, we show how ionic liquid design dictates polymer structure, which in turn can be harnessed to fine tune the mechanical properties of ionogels. With a level of control over gel structure beyond what is possible using molecular solvents, our systematic study thus provides insight into how ionic liquids can expand the design space for gel development for a broad range of applications.

Journal article

Al Ghatta A, Wilton-Ely JDET, Hallett JP, 2020, Efficient formation of 2,5-diformylfuran (DFF) in ionic liquids at high substrate loadings and low oxygen pressure with separation through sublimation, ACS Sustainable Chemistry & Engineering, Vol: 8, Pages: 2462-2471, ISSN: 2168-0485

The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using oxygen (1 atm) with a TEMPO and CuCl catalyst system is investigated using a range of imidazolium-based ionic liquids (ILs) and various bases at different HMF substrate loadings (10-50%). This represents the first example of HMF to DFF conversion in ionic liquid media under homogeneous catalysis conditions, revealing dramatic differences in performance between the ILs. In the non-coordinating, hydrophobic ionic liquid, [bmim][NTf2], 90% DFF yield is obtained at 5 mol% catalyst loading after 6 hours at 80 °C at a very high 40% HMF loading. Increasing the temperature to 100 °C leads to a lower yield, attributed to loss of volatile TEMPO from the reaction medium. A system using TEMPO and pyridine immobilized within the ionic liquid [bmim][NTf2] results in selective conversion of HMF to high purity DFF. It also allows the DFF formed to be isolated by sublimation in 81% yield before a further cycle is performed. Subsequent catalyst deactivation is probed by X-ray photoelectron spectroscopy (XPS). Synthesis from fructose in a two-step process achieves a 55% isolated DFF yield. This approach overcomes significant drawbacks previously reported for this transformation, such as solvent toxicity, separation and purification problems as well as the need for high oxygen pressures. Further oxidation of HMF with this system leads to a 62% yield of 5-formyl-2-furancarboxylic acid (FFCA). The separation of this compound can be achieved by sublimation of DFF followed by solvent extraction.

Journal article

Green S, Wheelhouse K, Payne A, Hallett J, Miller P, Bull Jet al., 2020, Thermal stability and explosive hazard assessment of diazo compounds and diazo transfer reagents, Organic Process Research and Development, Vol: 24, Pages: 67-84, ISSN: 1083-6160

Despite their wide use in academia as metal-carbene precursors, diazo compounds are often avoided in industry owing to concerns over their instability, exothermic decomposition and potential explosive behaviour. The stability of sulfonyl azides and other diazo-transfer reagents is relatively well understood, but there is little reliable data available for diazo compounds. This work firstly collates available sensitivity and thermal analysis data for diazo-transfer reagents and diazo compounds to act as an accessible reference resource. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) data for the model donor/acceptor diazo compound ethyl (phenyl)diazoacetate is presented. We also present a rigorous DSC dataset with 43 other diazo compounds, enabling direct comparison to other energetic materials to provide a clear reference work to the academic and industrial chemistry communities. Interestingly, there is a wide range of onset temperatures (Tonset) for this series of compounds which varied between 75 and 160 °C. The thermal stability variation depends on the electronic effect of substituents and the amount of charge delocalisation. A statistical model is demonstrated to predict the thermal stability of differently substituted phenyl diazoacetates. A maximum recommended process temperature (TD24) to avoid decomposition is estimated for selected diazo compounds. Average enthalpy of decomposition (∆HD) for diazo compounds without other energetic functional groups is −102 kJ mol−1. Several diazo transfer reagents are analyzed using the same DSC protocol and found to have higher thermal stability, which is in general agreement with reported values. For sulfonyl azide reagents an average ∆HD of −201 kJ mol−1 is observed. High quality thermal data from ARC experiments shows the initiation of decomposition for ethyl (phenyl)diazoacetate to be 60 °C , compared to 100 °C for t

Journal article

Upcraft T, Johnson R, Finnigan T, Hallett J, Guo Met al., 2020, Protein from Renewable Resources: Mycoprotein Production from Agricultural Residues, Computer Aided Chemical Engineering, Pages: 985-990

© 2020 Elsevier B.V. As concerns intensify over the increasing impact of human activities on the environment, efforts are underway in several areas in order to mitigate the worst effects. In recent years agricultural systems have received intense public scrutiny and if the global population increases, then the risk to food security is of real concern. Food-grade Single Cell Proteins (SCPs), produced through microbial fermentation, are an alternative to traditional livestock protein sources. This study presents a conceptual design and economic evaluation of SCP production from cellulosic-derived sugars from agricultural wastes. We modelled an SCP biorefinery, with ionic liquid pretreatment, enzymatic hydrolysis and fermentation to convert rice straw to food-grade protein. A Techno-Economic Analysis (TEA) was performed to assess the feasibility and compare the minimum selling price (MSP) to meat protein sources. Technical constraints were evaluated, in addition to evaluating the impact of reagent prices to the commercial success of the process.

Book chapter

Baaqel H, Tulus V, Chachuat B, Guillén-Gosálbez G, Hallett Jet al., 2020, Uncovering the True Cost of Ionic Liquids using Monetization, Computer Aided Chemical Engineering, Pages: 1825-1830

© 2020 Elsevier B.V. Due to their attractive properties, ionic liquids have found their way into many applications where they show high potential to replace existing chemicals. However, rising concerns over their ecological impacts, e.g., toxicity and biodegradability, and high cost have limited their use. Techno-economic and life cycle assessment studies were carried out to compare ionic liquids with existing solvents, yet the outcome of these analyses is often hard to interpret, as multiple metrics need to be considered simultaneously between which trade-offs exist. Here, for the first time the concept of monetization is coupled with process simulation and life cycle assessment to estimate the true cost of four lignocellulosic biomass pretreament solvents: triethylammonium hydrogen sulfate [TEA][HSO4], 1-methylimidazolium hydrogen sulfate [HMIM][HSO4], acetone from fossil sources and glycerol from renewable sources. The results show that monetized cost can be higher than or as high as the production cost. The real cost of production accounting for externalities can be more than 100% of direct costs estimated using conventional economic assessment methods. Our results show that [TEA][HSO4] has the lowest cost, while glycerol has the highest cost. We expect this to be a starting point for future studies targeting the design of more sustainable ionic liquids.

Book chapter

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