Publications
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Prado R, Weigand L, Zahari SMSNS, et al., 2017, An easy and reliable method for syringyl:guaiacyl ratio measurement, TAPPI JOURNAL, Vol: 16, Pages: 145-152, ISSN: 0734-1415
Prado R, Weigand L, Zahari SMSNS, et al., 2017, An easy and reliable method for syringyl: guaiacyl ratio measurement, TAPPI JOURNAL, Vol: 16, Pages: 145-152, ISSN: 0734-1415
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.
Lancefield CS, Rashid GMM, Bouxin F, et al., 2016, Investigation of the Chemocatalytic and Biocatalytic Valorization of a Range of Different Lignin Preparations: The Importance of beta-O-4 Content, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, Vol: 4, Pages: 6921-6930, ISSN: 2168-0485
De Gregorio GF, Prado R, Vriamont C, et al., 2016, Oxidative Depolymerization of Lignin Using a Novel Polyoxometalate-Protic Ionic Liquid System, ACS Sustainable Chemistry and Engineering, Vol: 4, Pages: 6031-6036, ISSN: 2168-0485
Oxidative depolymerization of lignin obtained from pine and willow can be achieved in a novel system encompassing the ionic liquid (IL) 1-butylimidazolium hydrogensulfate coupled with a vanadium based polyoxometalate (POM) under oxygen rich conditions. Along with an array of phenols and functionalized aromatics, vanillin and syringaldehyde were the main products extracted from the IL. The overall yield of aldehyde products were shown to be higher on lignin samples obtained with shorter pretreatment times, with vanillin being the exclusive aldehyde product obtained from pine. In the presence of molecular oxygen, the highest yield of aldehyde products was obtained when 5 wt % of the POM relative to the IL was employed and constituted the major product in the extracted oils. This system succeeds in exploiting the ability of ILs to depolymerize lignin and the remarkable properties of the POM to oxidize the lignin fragments into useful platform chemicals.
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.
Omoruyi U, Page S, Hallett J, et al., 2016, Homogeneous Catalyzed Reactions of Levulinic Acid: To γ-Valerolactone and Beyond, Chemsuschem, Vol: 9, Pages: 2037-2047, ISSN: 1864-564X
Platform chemicals derived from lignocellulosic plant biomass are viewed as a sustainable replacement for crude oil-based feedstocks. Levulinic acid (LA) is one such biomass-derived chemical that has been widely studied for further catalytic transformation to γ-valerolactone (GVL), an important ‘green’ fuel additive, solvent, and fine chemical intermediate. Although the transformation of LA to GVL can be achieved using heterogeneous catalysis, homogeneous catalytic systems that operate under milder reactions, give higher selectivities and can be recycled continuously are attracting considerable attention. A range of new homogeneous catalysts have now been demonstrated to efficiently convert LA to GVL and to transform LA directly to other value-added chemicals such as 1,4-pentanediol (1,4-PDO) and 2-methyltetrahydrofuran (2-MTHF). This Minireview covers recent advances in the area of homogeneous catalysis for the conversion of levulinic acid and levulinic ester derivatives to GVL and chemicals beyond GVL.
Hunt PA, Welton T, Hallett J, et al., 2016, Solubility of Alkali Metal Halides in the Ionic Liquid [C4C1im][OTf], Physical Chemistry Chemical Physics, Vol: 18, Pages: 16161-16168, ISSN: 1463-9084
The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl,CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li+, Na+and K+salts with anionsmatching the ionic liquid have been also investigated to determine how well these cations dissolve in[C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility ofsalts within this ionic liquid. The highest solubility found was for iodide salts and the lowestsolubility, for the three fluoride salts. There is no outstanding difference in the solubility of salts withmatching anions in comparison to halide salts. The experimental data were correlated employingseveral phase equilibria models, including ideal mixtures, van’t Hoff, the λh (Buchowski) equation,the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that thevan’t Hoff model gave the best correlation results. On the basis of the experimental data thethermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systemstogether with computed gas phase metathesis parameters. Dissolution depends on the energydifference between enthalpies of fusion and dissolution of the solute salt. This demonstrates thatovercoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionicliquids.
Brogan AP, Hallett JP, 2016, Solubilizing and stabilizing proteins in anhydrous lonic liquids through formation of protein-polymer surfactant nanoconstructs, Journal of the American Chemical Society, Vol: 138, Pages: 4494-4501, ISSN: 1520-5126
Nonaqueous biocatalysis is rapidly becoming a desirable tool for chemical and fuel synthesis in both the laboratory and industry. Similarly, ionic liquids are increasingly popular anhydrous reaction media for a number of industrial processes. Consequently, the use of enzymes in ionic liquids as efficient, environment-friendly, commercial biocatalysts is highly attractive. However, issues surrounding the poor solubility and low stability of enzymes in truly anhydrous media remain a significant challenge. Here, we demonstrate for the first time that engineering the surface of a protein to yield protein-polymer surfactant nanoconstructs allows for dissolution of dry protein into dry ionic liquids. Using myoglobin as a model protein, we show that this method can deliver protein molecules with near native structure into both hydrophilic and hydrophobic anhydrous ionic liquids. Remarkably, using temperature-dependent synchrotron radiation circular dichroism spectroscopy to measure half-denaturation temperatures, our results show that protein stability increases by 55 °C in the ionic liquid as compared to aqueous solution, pushing the solution thermal denaturation beyond the boiling point of water. Therefore, the work presented herein could provide a platform for the realization of biocatalysis at high temperatures or in anhydrous solvent systems.
Prado R, Brandt A, Erdocia X, et al., 2016, Depolymerisation of lignin by oxidation in ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
McIntosh AJS, Grasvik J, Griffith J, 2016, Methods of synthesis and purification of ionic liquids, Application, Purification, and Recovery of Ionic Liquids, Editors: Kuzmina, Hallett, Publisher: Elsevier, ISBN: 9780444637130
The book gives a description of the methods used for recovery and purification of ILs, a summary of the economic aspects of using ILs, and a review on the toxicity data of ILs.
Giarola S, Romain C, Williams C, et al., 2016, Techno-economic assessment of the production of phthalic anhydride from corn stover, Chemical Engineering Research & Design, Vol: 107, Pages: 181-194, ISSN: 1744-3563
Phthalic anhydride is used worldwide for an extremely broad range of applications spanning from the plastics industry to the synthesis of resins, agricultural fungicides and amines. This work proposes a conceptual design of a process for the production of phthalic anhydride from an agricultural residue (i.e. corn stover), energy integration alternatives as well as water consumption and life cycle greenhouse emissions assessment. The techno-economic and financial appraisal of the flowsheet proposed is performed. Results show how the valorization of all the carbohydrate-rich fractions present in the biomass as well as energy savings and integration is crucial to obtain an economically viable process and that it is in principle possible to produce renewable phthalic anhydride in a cost-competitive fashion with a lower impact on climate change compared to the traditional synthetic route.
Welton T, Matthews RP, Villar-Garcia IJ, et al., 2016, A structural investigation of ionic liquid mixtures, Physical Chemistry Chemical Physics, Vol: 18, Pages: 8608-8624, ISSN: 1463-9084
The structures of mixtures of ionic liquids (ILs) featuring a common 1-butyl-3-methylimidazolium ([C4C1im]+) cation butdifferent anions have been investigated both experimentally and computationally. 1H and 13C NMR of the ILs and theirmixtures has been performed both on the undiluted liquids and these diluted by CD2Cl2. These experiments have beencomplemented by quantum chemical density functional theory calculations and molecular dynamics simulations. Thesetechniques have identified the formation of preferential interactions between H2 of the imidazolium cation and the moststrongly hydrogen bond (H-bond) accepting anion. In addition, a preference for the more weakly H-bond accepting anionto interact above the imidazolium ring through anion-π+ interactions has been identified. The modelling of these data hasidentified that the magnitude of these preferences are small, of the order of only a few kJ mol−1, for all IL mixtures. Noclustering of the anions around a specific cation could be observed, indicating that these interactions arise from thereorientation of the cation within a randomly assigned network of anions. π+-π+ stacking of the imidazolium cations wasalso studied and found to be promoted by ILs with a strong H-bond accepting anion. Stacking interactions are easilydisrupted by the introduction of small proportions (< 50 mol%) of a weakly coordinating anion due to their propensity toform anion-π+ interactions. These results suggest that the formation of IL mixtures with different anions leads to subtlestructural changes of much lower energy than the Coulombic ordering of ions, accounting for why most IL mixtures exhibitideal, or nearly ideal, behaviour.
Kuzmina O, Hallett JP, 2016, Application, Purification, and Recovery of Ionic Liquids, ISBN: 9780444637130
Application, Purification, and Recovery of Ionic Liquids provides a comprehensive overview of the usage of ionic liquids (IL). The book gives a description of the methods used for recovery and purification of ILs, a summary of the economic aspects of using ILs, and a review on the toxicity data of ILs. It is written for researchers, scientists, and engineers working with ILs, their properties, and usages. The book not only describes the chemical aspects, but the economic and environmental aspects as well, making it of particular interest to professionals applying this technology. Chapters written by scientists in academia and researchers in industry, ensuring coverage of both the scientific fundaments and industrial applications. A single source of information for a broad collection of recovery and purification methods. Provides information on using ionic liquids as green solvents. Includes economic aspects of recovery and reuse of ionic liquids.
Brandt A, Chen L, van Dongen BE, et al., 2015, Structural changes in lignins isolated using an acidic ionic liquid water mixture, Green Chemistry, Vol: 17, Pages: 5019-5034, ISSN: 1463-9262
Recently, acidic ionic liquid water mixtures based on the hydrogen sulfate anion have been shown to effectively extract lignin from lignocellulosic biomass. This study analyses Miscanthus giganteus lignin isolated after extraction with the protic ionic liquid 1-butylimidazolium hydrogen sulfate ([HC4im][HSO4]) followed by precipitation with the antisolvent water. Several analytical techniques were employed, such as quantitative 13C-NMR, 1H–13C HSQC NMR, 31P-NMR, Py-GC-MS, GPC and elemental analysis. The analysis shows that the ionic liquid pretreatment breaks lignin-hemicellulose linkages and depolymerizes the lignin through the cleavage of glycosidic, ester and β-O-4 ether bonds. This is accompanied by solubilization of the newly generated lignin fragments. At longer pretreatment times, repolymerization of lignin fragments through condensation reactions occurs. The isolated lignins were carbohydrate-free, had low sulfur contents, low molecular weights. Early stage lignins were structurally similar to ball-milled lignin, while more treated lignins were enriched in p-hydroxyphenyl and guaiacyl units and had a high phenolic hydroxyl group content. We conclude that, depending on the treatment conditions, lignins with a variety of characteristics can be isolated using this type of ionic liquid solution.
Prado R, Brandt A, Erdocia X, et al., 2015, Lignin oxidation and depolymerisation in ionic liquids, Green Chemistry, Vol: 18, Pages: 834-841, ISSN: 1463-9262
The depolymerisation of lignin directly in the black liquor was studied, comparing two ionic liquids as extracting solvents (butylimidazolium hydrogen sulphate and triethylammonium hydrogen sulphate), under oxidising conditions. H2O2 was chosen as the oxidant agent. It was observed that lignins derived from butylimidazolium hydrogen sulphate were more susceptible to degradation. The main degradation products found in the extracted oils were aromatic acids, such as vanillic acid, benzoic acid and 1,2-benzenedicarboxylic acid.
Brandt A, Hallett JP, 2015, Low-cost ionic liquids for wood fractionation, Pages: 462-466
Pretreatment of lignocellulosic biomass is the first step in the production of chemicals and fuels from woody biomass. It is also of the most expensive steps and has many implications on down-stream processes. Hence pretreatment technologies must be developed that are have low cost and provide high-quality substrates for subsequent chemical and biological transformations. To optimise cost, valorisation of all components contained in the lignocellulosic feedstock is required, including the hemicellulose and the lignin. A novel pretreatment technology is the application of low-cost ionic liquid water mixtures.
Cadogan SP, Hallett JP, Maidand GC, et al., 2015, Diffusion Coefficients of Carbon Dioxide in Brines Measured Using <SUP>13</SUP>C Pulsed-Field Gradient Nuclear Magnetic Resonance, JOURNAL OF CHEMICAL AND ENGINEERING DATA, Vol: 60, Pages: 181-184, ISSN: 0021-9568
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- Citations: 19
Giarola S, Romain C, Williams CK, et al., 2015, Production of phthalic anhydride from biorenewables: process design, 12TH INTERNATIONAL SYMPOSIUM ON PROCESS SYSTEMS ENGINEERING AND 25TH EUROPEAN SYMPOSIUM ON COMPUTER AIDED PROCESS ENGINEERING, PT C, Vol: 37, Pages: 2561-2566, ISSN: 1570-7946
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George A, Brandt A, Tran K, et al., 2014, Design of low-cost ionic liquids for lignocellulosic biomass pretreatment, Green Chemistry, Vol: 17, Pages: 1728-1734, ISSN: 1744-1560
The cost of ionic liquids (ILs) is one of the main impediments to IL utilization in the cellulosic biorefinery, especially in the pretreatment step. In this study, a number of ionic liquids were synthesized with the goal of optimizing solvent cost and stability whilst demonstrating promising processing potential. To achieve this, inexpensive feedstocks such as sulfuric acid and simple amines were combined into a range of protic ionic liquids containing the hydrogen sulfate [HSO4]− anion. The performance of these ionic liquids was compared to a benchmark system containing the IL 1-ethyl-3-methylimidazolium acetate [C2C1im][OAc]. The highest saccharification yields were observed for the triethylammonium hydrogen sulfate IL, which was 75% as effective as the benchmark system. Techno-economic modeling revealed that this promising and yet to be optimized yield was achieved at a fraction of the processing cost. This study demonstrates that some ILs can compete with the cheapest pretreatment chemicals, such as ammonia, in terms of effectiveness and process cost, removing IL cost as a barrier to the economic viability of IL-based biorefineries.
Gschwend FJV, Hallett JP, Fennell PS, 2014, Towards a cost efficient production of fuels from lignocellulosic biomass using ionic liquids, 248th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
De Gregorio GF, Welton T, Hallett JP, 2014, Elucidating the mechanism of lignin depolymerisation using acidic ionic liquids: A focus on ether cleavage, 248th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Ismail NL, Trang QT, Hallett JP, et al., 2014, Nucleophilic substitution of benzyl alcohol with hydrogensulfate ionic liquids, 248th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Hallett JP, Brandt A, 2014, Low cost ionic liquids for biorefining, 248th National Meeting of the American-Chemical-Society (ACS), Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Mac Dowell N, Llovell F, Sun N, et al., 2014, New Experimental Density Data and soft-SAFT Models of Alkylimidazolium ([CnC₁im](+)) Chloride (Cl-), Methylsulfate ([MeSO4](-)), and Dimethylphosphate ([Me2PO4](-)) Based Ionic Liquids, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 118, Pages: 6206-6221, ISSN: 1520-6106
Chen L, Sharifzadeh M, Mac Dowell N, et al., 2014, Inexpensive ionic liquids: [HSO₄]¯-based solvent production at bulk scale, Green Chemistry, Vol: 16, Pages: 3098-3106, ISSN: 1463-9262
Through more than two decades’ intensive research, ionic liquids (ILs) have exhibited significant potential in various areas of research at laboratory scales. This suggests that ILs-based industrial process development will attract increasing attention in the future. However, there is one core issue that stands in the way of commercialisation: the high cost of most laboratory-synthesized ILs will limit application to small-scale, specialized processes. In this work, we evaluate the economic feasibility of two ILs synthesized via acid–base neutralization using two scenarios for each: conventional and intensification processing. Based upon our initial models, we determined the cost price of each IL and compared the energy requirements of each process option. The cost prices of triethylammonium hydrogen sulfate and 1-methylimidazolium hydrogen sulfate are estimated as $1.24 kg−1 and $2.96–5.88 kg−1, respectively. This compares favourably with organic solvents such as acetone or ethyl acetate, which sell for $1.30–$1.40 kg−1. Moreover, the raw materials contribute the overwhelming majority of this cost and the intensified process using a compact plate reactor is more economical due to lower energy requirements. These results indicate that ionic liquids are not necessarily expensive, and therefore large-scale IL-based processes can become a commercial reality.
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