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

离子液体(ILS)由于其可调的物理化学性质，在许多过程中是越来越受欢迎的替代溶剂1，它们被用于催化、2电沉积3、4和生物质的有价化，特别是在从木材生物质中高效溶解和回收木质素方面。为了使更多可行的工业过程能够利用离子液体，需要对每一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经受高温过程，从而在原则上具有很高的可回收性，但它们的合成成本往往很高。许多ILS对木质素具有很高的溶解度，水是一种廉价的抗溶剂，这使得这些ILS成为从生物质中分离木质素的有趣溶剂，并用于木质素提纯和纤维形成。最近报道的质子型硫酸氢离子液体在木材分馏工业中显示出特别有潜力的潜力，其散装溶剂成本低至1.87公斤-1.6美元，7然而，人们对这些离子液体的热性质知之甚少。因此，该项目的一个目标是提供关于低成本离子液体木质素溶解稳定性和分解机理的全面的动力学和热力学数据，并将研究这些离子液体降解时的汽相组成。该项目的第二个目标是生产溶解木质素的离子液体，在感兴趣的温度下显示液晶相的各向异性行为。这是一个假设，木素基碳纤维迄今的性能不令人满意的是原丝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结构域的形成，从而限制了所得到的碳纤维的强度和硬度。该项目将使用各向同性的硫酸氢离子液体以及新型离子液晶，研究这两种类型的离子液体是否能够帮助生产更有序的前体纤维，这应该会导致更坚固、更便宜、更可持续的碳纤维。ILS将被用来修饰木质素，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，为了实现纤维生产，该项目将开发一种加热微挤出机，可用于极小规模(1克)的木质素纤维熔融纺丝或木质素纤维的热湿法纺丝，加热有助于降低纺丝原液的粘度，从而增加离子液体原液中的聚合物含量，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.