Acid-base conjugate ionic liquids in lignocellulose processing : synthesis, properties and applications

As the consumption of natural resources increase with the exponential world population growth, the food industry needs to answer the demand. This means that farming has to be increased and optimized from its current level. The problem is summoned from the fact that the amount of arable land is decreasing. This eventually leads to prioritizing the land for food crops and the downscaling the production of i.e. palm oil and cotton. Cotton is ~90% pure cellulose and is used for textile commodities for its properties over synthetic fibers. The same cellulose can be found all around in nature, from the structure of trees to algae. Cellulose is the world s most commonly found polymer and it is generated annually in nature enough to stop cotton farming altogether. The problem is the low solubility of cellulose to commonly used solvents. The extensive hydrogen bonding network of cellulose gives this biopolymer its strong features. The structure of cellulose and the chemical features has been known for a century and a half to this date, but solubilization of cellulose has evaded a more systemic, yet pragmatic approach. There have been introductions of various types of solvent systems for cellulose dissolution, from which ionic liquids have been the most successful class of solvents. The research performed in this thesis has been focusing on the research and development of new cellulose dissolving ionic liquids. A class of imidazolium based ionic liquids was used as the starting point for the development, since they exhibit high dissolutive power and relatively low viscosities. The chemical stability of the solvent system needs to sustain various kinds of chemical and physical stress without compromising process safety, ecology or economy. Our research indicated that the acidity-basicity of the ionic liquid components was correlating with the chemical-physical stability of the solvents. The higher the basicity was the less stable the ionic liquid become and in the same time it was found out that the ionic liquids that were synthesized from less basic components were not able to dissolve cellulose in the first place. We calculated the gas-phase basicities (proton affinity) of various types and strengths of bases by using simple and efficient computational method. After the calculations were done, we combined the bases with acetic acid to form acetate ionic liquids and with propionic acid for propionates correspondingly. After the examination of the cellulose dissolution capability we discovered a threshold basicity where the cellulose dissolution capability was introduced. In a collaboration with Aalto University, we developed an ionic liquid that could be used in industrial scale production of cellulose fibers. The research was steered towards investigation of the chemical stability and recyclability of this new ionic liquid.Selluloosa on maailman yleisin luonnonpolymeeri, jota luonto tuottaa tonneittain vuodessa. Selluloosaa kasvaa luonnossa kasvien tukirakenteissa, missä se on sidoksissa mm. ligniiniin ja hemiselluloosaan. Puuvillassa puhtaan selluloosan määrä on lähellä 90% ja täten se on ollut erinomainen selluloosan lähde esim. tekstiiliteollisuudelle. Selluloosan sisäisen rakenteen ansiosta sitä on erittäin vaikea saada liukenemaan tyypillisiin liuottimiin. Liukoisessa muodossakin se muodostaa erittäin matalan viskositeetin liuoksia, mikä hankaloittaa prosessointia. Näitä liuottimia on kehitetty viimeisen 100 vuoden aikana muutamia, joista vain kourallinen on päätynyt teollisten sovelluksien käyttöön. Tässä tutkimuksessa halusimme perehtyä selluloosan liuottimien, etenkin ionisten nesteiden, kykyyn liuottaa selluloosaa ja hyödyntää tätä tietoa uusien ionisten nesteiden suunnittelussa mahdollisia kaupallisia sovelluksia varten