Ning Sun

Physical Properties of Ionic Liquids: Database and Evaluation

A comprehensive database on physical properties of ionic liquids (ILs), which was collected from 109 kinds of literature sources in the period from 1984 through 2004, has been presented. There are 1680 pieces of data on the physical properties for 588 available ILs, from which 276 kinds of cations and 55 kinds of anions were extracted. In terms of the collected database, the structure-property relationship was evaluated. The correlation of melting points of two most common systems, disubstituted imidazolium tetrafluoroborate and disubstituted imidazolium hexafluorophosphate, was carried out using a quantitative structure-property relationship method.

Complete dissolution and partial delignification of wood in the ionic liquid 1-ethyl-3-methylimidazolium acetate

Both softwood (southern yellow pine) and hardwood (red oak) can be completely dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) after mild grinding. Complete dissolution was achieved by heating the sample in an oil bath, although wood dissolution can be accelerated by microwave pulses or ultrasound irradiation. It has been shown that [C2mim]OAc is a better solvent for wood than 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and that variables such as type of wood, initial wood load, particle size, etc. affect dissolution and dissolution rates; for example, red oak dissolves better and faster than southern yellow pine. Carbohydrate-free lignin and cellulose-rich materials can be obtained by using the proper reconstitution solvents (e.g., acetone/water 1 : 1 v/v) and approximately 26.1% and 34.9% reductions of lignin content in the reconstituted cellulose-rich materials (from pine and oak, respectively) have been achieved in one dissolution/reconstitution cycle. The regenerated cellulose-rich materials and lignin fractions were characterized and compared with the original wood samples and biopolymer standards. For pine, 59% of the holocellulose (i.e., the sum of cellulose and hemicellulose) in the original wood can be recovered in the cellulose-rich reconstituted material; whereas 31% and 38% of the original lignin is recovered, respectively, as carbohydrate-free lignin and as carbohydrate-bonded lignin in the cellulose-rich material.

Dissolution or extraction of crustacean shells using ionic liquids to obtain high molecular weight purified chitin and direct production of chitin films and fibers

1-Ethyl-3-methyl-imidazolium acetate can completely dissolve raw crustacean shells, leading to recovery of a high purity, high molecular weight chitin powder and to fibers and films which can be spun directly from the extract solution.

Rapid dissolution of lignocellulosic biomass in ionic liquids using temperatures above the glass transition of lignin

Rapid dissolution of bagasse and southern yellow pine has been achieved in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) by using a dissolution temperature above the glass transition of lignin (ca. 150 °C). When 0.5 g of bagasse or pine is added to 10 g of [C2mim]OAc, complete dissolution can be obtained in 5–15 min for bagasse at a temperature of 175–195 °C, compared to 15–16 h at 110 °C, and over 90% of added pine can be dissolved with heating at 175 °C for 30 min. Upon regeneration in acetone/water, lignin and carbohydrate can be partially separated as lignin and a cellulose-rich material (CRM, pulp). Compared to published methods with lower temperatures and longer times (e.g., 110 °C, 16 h), processing bagasse in [C2mim]OAc at 185 °C for 10 min results in higher yields of both recovered lignin (31% vs. 26% of the available lignin) and carbohydrate (carbohydrate yield = 66% vs. 63% of the available carbohydrate). In addition, the CRM pulp recovered using the higher temperature method has much lower residual lignin content (6% vs. 20%). Similar results were obtained for pine (lignin content in CRM with higher vs. lower temperature method = 16.1% vs. 23.5%). The IL was recycled and reused although the efficiency decreased and ca. 15% of the IL had degraded after the higher temperature process. These latter results suggest further optimization of the choice of IL and heating conditions might be needed to develop an energy and chemical efficient process.

Magnetite-embedded cellulose fibers prepared from ionic liquid

A dry-jet wet spinning process for making magnetically active cellulose fibers has been developed using the ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl). Cellulose from different sources with various degrees of polymerization (DP) was used for making fibers by first dissolving the cellulose in the IL, dispersing particles of magnetite in the solution, and then coagulating the fibers in a water bath under appropriate spinning conditions. The variation of fiber properties with cellulose source and concentration of magnetite is discussed. Fiber texture was found to be related to overall magnetite concentration, cellulose concentration, and molecular weight in the spinning solution. In general, it was found that increasing DP and/or cellulose concentration resulted in more robust fibers, and conversely the addition of magnetite particles weakened the overall mechanical properties.

Use of Polyoxometalate Catalysts in Ionic Liquids to Enhance the Dissolution and Delignification of Woody Biomass

A well-known polyoxometalate, [PV₂Mo₁₀O₄₀]⁵⁻, in both acidic (acidic POM, H₅[PV₂Mo₁₀O₄₀]) and ionic liquid-compatible form ([C₂mim]POM, [1-ethyl-3-methylimidazolium]₄H[PV₂Mo₁₀O₄₀]), has been studied as a catalyst for the dissolution and delignification of wood in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C(2) mim]OAc). Differences were observed with variables such as the form of POM, POM loading, and reaction conditions. Generally, the addition of POM leads to a faster dissolution, a lower lignin content in the recovered cellulose-rich materials (isolated pulp), and a lower isolated yield of lignin due to its oxidation. Acidic POM decreases the lignin content of the pulp without compromising the yield of the pulp. [C₂mim]POM in the IL facilitates greater delignification (lower lignin content in pulp) than the IL with acidic POM; however, the overall pulp yield is also lower indicating some degradation of the carbohydrates. The POM can be recovered with [C₂mim]OAc after evaporation of the reconstitution solvent (e.g., acetone/water) and can be reused, albeit with some loss of POM and loss of POM activity under the current conditions.

Composite fibers spun directly from solutions of raw lignocellulosic biomass dissolved in ionic liquids

Lignocellulosic biomass composite fibers (southern yellow pine and bagasse) were successfully prepared directly from the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C2mim]OAc) with a dry-jet wet spinning process using short dissolution times (10–30 min) and temperatures above the glass transition temperature of lignin. Fibers could not be spun at all from solutions of pine dissolved using previously reported dissolution methods (110 °C, 16 h), while bagasse fibers spun using the higher temperature/shorter time method were stronger than those obtained using the lower temperature/longer time method.