Developing and understanding lignin dissolving ionic liquids for sustainable carbon fibre production from lignin

离子液体由于其可调节的物理化学性质，在许多工艺中成为越来越受欢迎的替代溶剂它们被用于催化、电沉积和生物质增值，特别是用于木材生物质中木质素的高产溶解和回收。为了利用离子液体实现大量可行的工业过程，需要对每种表现出良好性能的离子液体进行成本和安全性评估。虽然已知某些离子液体能够承受高温过程，从而在原则上具有高可回收性，但它们的合成成本往往很高。许多il对木质素具有高溶解度，水是一种廉价的抗溶剂，这使得这些il成为从生物质中分离木质素和用于木质素净化和纤维形成的有趣溶剂。最近报道的硫酸氢质子离子液体作为木材分馏的工业候选物显示出特别有前景的潜力，其散装溶剂成本低至1.87美元kg-1.6,7然而，这些离子液体的热性能尚不清楚。因此，本项目的目的之一是获得有关木质素溶解低成本离子液体的稳定性和分解机制的综合动力学和热数据，并研究这些离子液体降解时的气相组成。该项目的第二个目标是生产木质素溶解离子液体，在感兴趣的温度下显示液晶相的各向异性行为。有一种假设认为，迄今为止，木质素基碳纤维的性能不理想是由于前体纤维中木质素聚合物的无序排列，这似乎限制了碳化过程中有序石墨畴的形成，从而限制了碳纤维的强度和刚度。使用各向同性硫酸氢离子液体和新型离子液晶，该项目将研究这两种类型的离子液体是否有助于生产更有序的前体纤维，从而产生更强、更便宜、更可持续的碳纤维。il将用于修饰木质素，作为提取的一部分或作为提取后的纯化步骤。作为第三个目标，为了使纤维生产成为可能，该项目将开发一种加热微挤出机，可用于木质素纤维的熔融纺丝或木质素纤维的热湿纺丝，其规模非常小（<1克），热量有助于降低纺丝涂料的粘度，从而增加离子液体涂料中的聚合物负荷，从而提高加工经济性。

Ionic liquids (ILs) are increasingly popular alternative solvents for many processes, due to their tuneable physicochemical properties.1 They are utilised in catalysis,2 electrodeposition3,4 and biomass valorisation, in particular, in the high yielding dissolution and recovery of lignin from wood biomass. In order to enable a larger numbers of viable industrial processes utilising ionic liquids, both cost and safety need to be assessed for each ionic liquid that shows promising performance. While certain ionic liquids are known to be able to withstand high-temperature processes, resulting in high recyclability in principle, they are often expensive to synthesise. A number of ILs have been shown to have high solubility for lignin, with water being an inexpensive antisolvent, which makes these ILs interesting solvents for isolating lignin from biomass and for use in lignin purification and in fibre formation. Recently reported protic hydrogen sulfate ionic liquids have shown particular promising potential as industrial candidates for wood fractionation, with bulk solvent cost as low as $1.87 kg-1.6,7 However, the thermal properties of these ILs are poorly understood. Hence, one aim of this project is to produce comprehensive kinetic and thermal data regarding the stability and decomposition mechanisms of lignin dissolving low-cost ILs, and the vapour phase composition upon degradation of these ionic liquids will be studied. A second aim of the project is to produce lignin dissolving ionic liquids that display the anisotropic behaviour of liquid crystals phases at temperatures of interest. It is the hypothesis that the unsatisfactory performance of lignin based carbon fibres to date is the disordered arrangement of the lignin polymers in the precursor fibres, which appears to limit the formation of ordered graphitic domains during carbonisation and hence the strength and stiffness of resulting carbon fibres. Using isotropic hydrogen sulfate ionic liquids as well as the novel ionic liquid crystals, the project will investigate whether either type of ionic liquid can help produce more ordered precursor fibres, which should result in stronger, cheaper, more sustainable carbon fibres. The ILs will be used to modify the lignin either as part of the extraction or as a post-extraction purification step. As a third aim, to enable fibre production, the project will develop a heated microextruder, which can be used for melt-spinning lignin fibres or for hot wet-sinning of lignin fibres at a very small (<1 g) scale, with the heat helping to reduce the viscosity of the spinning dope, which increases polymer loading in the ionic liquid dopes and hence improving processing economics.