Arno Parviainen

Predicting Cellulose Solvating Capabilities of Acid-Base Conjugate Ionic Liquids

Different acid-base conjugates were made by combining a range of bases and superbases with acetic and propionic acid. Only the combinations that contained superbases were capable of dissolving cellulose. Proton affinities were calculated for the bases. A range, within which cellulose dissolution occurred, when combined with acetic or propionic acid, was defined for further use. This was above a proton affinity value of about 240 kcal mol(-1) at the MP2/6-311+G(d,p)//MP2/ 6-311+G(d,p) ab initio level. Understanding dissolution allowed us to determine that cation acidity contributed considerably to the ability of ionic liquids to dissolve cellulose and not just the basicity of the anion. By XRD analyses of suitable crystals, hydrogen bonding interactions between anion and cation were found to be the dominant interactions in the crystalline state. From determination of viscosities of these conjugates over a temperature range, certain structures were found to have as low a viscosity as 1-ethyl-3-methylimidazolium acetate, which was reflected in their high rate of cellulose dissolution but not necessarily the quantitative solubility of cellulose in those ionic liquids. 1,5-Diazabicyclo[4.3.0]non-5-enium propionate, which is one of the best structures for cellulose dissolution, was then distilled using laboratory equipment to demonstrate its recyclability.

Relative and inherent reactivities of imidazolium-based ionic liquids: the implications for lignocellulose processing applications

Novel methods for the fractionation of wood, as a major renewable chemical and material feedstock, are in demand. Ionic liquids, such as 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), are promoted as potential media for these processes. However, the chemical stabilities of such ionic liquids are in question as they may have an effect on process sustainability or efficiency. With anion nucleophilicity and basicity being implicated more in ionic liquid reactivity, a rough scale of the relative reactivities for [emim]-based ionic liquids is demonstrated, based upon their TGA decomposition temperatures. These values are compared to the proton affinities for the anions of those ionic liquids, as a crude measure of nucleophilicity or basicity. The implications for the temperature-dependent chemical stability of imidazolium-based ionic liquids are discussed, in regard to their interactions with wood biopolymers. It is observed that for ionic liquids with less diffuse anions (more nucleophilic or basic), such as [emim][OAc], they unfortunately become more unstable. This is exhibited by a decrease in the thermal stability and an increase in the degree of interaction with the biomass, to the point of better solvation and even covalent interactions with dissolved components. The ab initio proton affinities, dipole moments, van der Waals surface area, and volumes, are presented for an extended series of anions, commonly used in ionic liquids.

Cellulose hydrolysis with thermo- and alkali-tolerant cellulases in cellulose-dissolving superbase ionic liquids

Pretreatment with ionic liquids (ILs) is known to greatly increase the subsequent biomass hydrolysis with enzymes. However, the presence of even low amounts of ILs has negative effects on cellulase action. Most studies on cellulase inactivation by ILs have focused on imidazolium-based ILs, which until recently were one of the few IL classes known to dissolve cellulose. In this article we describe results of cellulase action in matrices containing ILs belonging to two IL classes recently reported as cellulose solvents. These ILs are based on the organic superbases 1,1,3,3-tetramethylguanidine (TMG) or 1,5-diazabicyclo[4.3.0]non-5-ene (DBN). In this study commercial thermo- and alkaline stabile cellulase products were employed, as these were anticipated to also have a higher stability in ILs. For comparison, hydrolysis experiments were also carried out with a well-characterised endoglucanase (Cel5A) from Trichoderma reesei and in matrices containing 1-ethyl-3-methylimidazolium acetate, [EMIM]AcO. Two different substrates were used, microcrystalline cellulose (MCC) and eucalyptus pre-hydrolysis kraft dissolving grade pulp. The hydrolysis yields were on the same level for both of these substrates, but decreases in molecular weight of the cellulose was observed only for the dissolving grade pulp. By using commercial cellulases with good thermo- and alkali-stability some benefits were obtained in terms of IL compatibility. Enzyme thermostability correlated with higher hydrolysis yields in IL-containing matrices, whereas activity at high pH values did not offer benefits in terms of IL tolerance. The new classes of cellulose-dissolving superbase ILs did not differ in terms of cellulase compatibility from the well-studied imidazolium-based ILs. Of the novel superbase ILs tested, [TMGH]AcO was found to inhibit the enzymatic hydrolysis the least.

On the solubility of wood in non-derivatising ionic liquids

Norway spruce wood was mechanically pulverized to varying degrees. The solubility of the wood samples, in a range of common ionic and molecular solvents, was quantified using a novel 31P NMR technique. The results show that intact wood is not soluble under mild treatment conditions, in cellulose-dissolving or swelling solvents.

Ionic Liquids for the Production of Man-Made Cellulosic Fibers: Opportunities and Challenges

The constant worldwide increase in consumption of goods will also affect the textile market. The demand for cellulosic textile fibers is predicted to increase at such a rate that by 2030 there will be a considerable shortage, estimated at ~15 million tons annually. Currently, man-made cellulosic fibers are produced commercially via the viscose and Lyocell™ processes. Ionic liquids (ILs) have been proposed as alternative solvents to circumvent certain problems associated with these existing processes. We first provide a comprehensive review of the progress in fiber spinning based on ILs over the last decade. A summary of the reports on the preparation of pure cellulosic and composite fibers is complemented by an overview of the rheological characteristics and thermal degradation of cellulose–IL solutions. In the second part, we present a non-imidazolium-based ionic liquid, 1,5-diazabicyclo[4.3.0]non-5-enium acetate, as an excellent solvent for cellulose fiber spinning. The use of moderate process temperatures in this process avoids the otherwise extensive cellulose degradation. The structural and morphological properties of the spun fibers are described, as determined by WAXS, birefringence, and SEM measurements. Mechanical properties are also reported. Further, the suitability of the spun fibers to produce yarns for various textile applications is discussed.

Sustainability of cellulose dissolution and regeneration in 1,5-diazabicyclo[4.3.0]non-5-enium acetate: a batch simulation of the IONCELL-F process

The recyclability of 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]), as a direct dissolution solvent for cellulose, was evaluated during laboratory scale recycling trials. The main objective was to simulate the conditions of a spinning bath from a Lyocell-type air-gap spinning process, called the IONCELL-F process. The saline solution was then concentrated, recycled and reused as many times as possible before cellulose dissolution was no longer possible. The chemical compositions of the ionic liquid and pulp were recorded throughout the experiments. The results of the experiments showed that [DBNH][OAc] can be recycled from aqueous media with an average recovery rate of 95.6 wt% using basic laboratory equipment, without any further process intensification or optimisation. The recycling of the ionic liquid did not change the chemical composition or degree of polymerisation of the recovered pulp but the colour of the regenerated pulps gradually darkened as the recycling times increased. The ionic liquid was found to hydrolyse 6.0–13.6 mol% per cycle, under these conditions. The build-up of the hydrolysis product, 3-(aminopropyl)-2-pyrrolidonium acetate, killed the dissolution feature at between 30.6–45.6 wt% hydrolysis product. The enzymatic digestibility of the regenerated pulp samples was studied with both a monocomponent endoglucanase and a cellulase mixture. The amount of residual [DBNH][OAc] in the regenerated pulps was determined, by both NMR and capillary electrophoresis. Although hydrolysis of the ionic liquid occurs, this study clearly shows potential for industrial application, with appropriate process equipment and recycling conditions.

Dissolution enthalpies of cellulose in ionic liquids.

In this work, interactions between cellulose and ionic liquids were studied calorimetrically and by optical microscopy. Two novel ionic liquids (1,5-Diazabicyclo[4.3.0]non-5-enium propionate and N-methyl-1,5-diazabicyclo[4.3.0]non-5-enium dimethyl phosphate) and 1-ethyl-3-methylimidazolium acetate-water mixtures were used as solvents. Optical microscopy served in finding the extent of dissolution and identifying the dissolution pattern of the cellulose sample. Calorimetric studies identified a peak relating to dissolution of cellulose in solvent. The transition did, however, not indicate complete dissolution, but rather dissolution inside fibre or fibrils. This method was used to study differences between four cellulose samples with different pretreatment or origins.

Efficiency of hydrophobic phosphonium ionic liquids and DMSO as recyclable cellulose dissolution and regeneration media

Hydrophobic, long-chain tetraalkylphosphonium acetate salts (ionic liquids) were combined with a dipolar aprotic co-solvent, dimethylsulfoxide (DMSO), and the feasibility of these solvent systems for cellulose dissolution and regeneration was studied. A 60 : 40 w/w mixture of the ionic liquid tetraoctylphosphonium acetate ([P8888][OAc]) and DMSO was found to dissolve up to 8 wt% cellulose, whilst trioctyl(tetradecyl)phosphonium acetate ([P14888][OAc]) dissolved up to 3 wt% cellulose. Water (an anti-solvent for cellulose) was found to give rise to biphasic liquid–liquid systems when combined with these mixtures, yielding an upper phase rich in ionic liquid and a lower aqueous phase. The liquid–liquid equilibria of the ternary systems were experimentally determined, finding that DMSO strongly partitioned towards the aqueous phase. Thus, a process scheme involving simultaneous regeneration of cellulose and recycling of the solvent system was envisioned, and demonstrated on a large scale using [P8888][OAc]. A large portion of the ionic liquid (ca. 60 wt%) was directly recovered via phase separation, with a further 37 wt% being recovered from the swollen cellulose phase and residual materials, bringing recovery to 97%. XRD analysis of the recovered cellulose materials showed a loss of crystallinity and conversion from Cellulose I to Cellulose II. Non-dissolving compositions of ionic liquid and DMSO did not affect cellulose crystallinity after cellulose pulp treatment.

Practical Aerobic Oxidation of Alcohols: Ligand Enhanced TEMPO/Mn(NO3)2 Catalyst System

A highly efficient, ligand‐enhanced 2,2,6,6‐tetramethylpiperidine‐1‐oxy (TEMPO)/Mn(NO3)2 catalyst system for the aerobic oxidation of alcohols is described. From the series of coordinating ligands studied herein, 2‐picolinic acid (PyCOOH) improves the catalytic activity of TEMPO/Mn(NO3)2 remarkably. Under ambient air at room temperature in acetic acid, the ligand‐enhanced catalyst converts aliphatic and benzylic primary alcohols that bear various functional groups into their respective aldehydes with near quantitative conversions. The applicability of the catalyst for convenient preparative synthesis was demonstrated by conducting oxidations on a gram scale. A change of TEMPO to the sterically less demanding 9‐azabicyclo[3.3.1]nonane N‐oxyl results in a Mn catalyst that is also able to oxidize secondary alcohols to ketones. Mechanistic studies showed that alcohols are oxidized by the oxoammonium cation derived from the nitroxyl radical. The active oxidant is regenerated by Mn(NO3)2, and this process is greatly promoted by the coordination of PyCOOH to Mn.

Selective Aerobic Oxidation of Alcohols with NO3 − Activated Nitroxyl Radical/Manganese Catalyst System

A homogeneous Mn(NO3)2/2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl/2‐picolinic acid catalyst system is highly active and versatile for the selective aerobic oxidation of alcohols (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl=TEMPO, 2‐picolinic acid=PyCOOH). The catalytic method enables near quantitative conversion of various primary alcohols to the respective aldehydes using a very simple reaction setup and workup. This study presents findings on the catalyst stability and mechanisms of deactivation. The results show that NO3− plays a crucial catalytic role in the reaction as a source of oxygen activating NOx species. Yet, disproportionation of NO3− to the volatile NO2 during the reaction leads to catalyst deactivation under open air conditions. Catalyst deactivation through this route can be overcome by adding a catalytic amount of nitrate salt, for example NaNO3 into the reaction. This stabilizes the Mn(NO3)2/TEMPO/PyCOOH catalyst and enables oxidation of various primary alcohols to the respective aldehydes using low catalyst loadings under ambient conditions. Secondary alcohols can be oxidized with a modified catalyst utilizing sterically accessible nitroxyl radical 9‐azabicyclo[3.3.1]nonane N‐oxyl (ABNO) instead of TEMPO. At the end of the alcohol oxidation, pure carbonyl products and the reusable catalyst can be recovered simply by extracting with organic solvent and dilute aqueous acid, followed by evaporation of both phases.