Value recovery from organic waste
Creators: name: Kewcharoenwong, Pajaree
Publisher: name: Imperial College London
Year: 2012

description: Organic waste has been recognised as a major problem in waste management worldwide. Material recovery of key value components from organic waste using a series of novel solvents, ionic liquids (ILs), has been investigated as a potential sustainable management solution. The overall aim of the research described in this thesis is to develop novel methodologies based on ionic liquid extraction that fractionates and recovers value from organic waste either as a source of energy or as a source of feedstock for the chemical and related industries. The results of this investigation are presented in terms of: (i) the synthesis and characterisation of ILs, using microwave-assisted methods and conventional organic synthesis; (ii) the solubility measurements of key food and food-related components in a suite of prepared ILs; (iii) the use of ILs in the recovery of key value components from organic waste streams; and (iv) the development and trialling of a novel IL mix as a dual solvent for extraction and subsequent conversion of key value components into value-added products in a selected organic waste stream. A suite of eight imidazolium and pyridinium-based ionic liquids is prepared, by microwave-assisted technology, and for comparison purposes by conventional organic synthesis methods. The extent of solubilities of pure food and food-related components in ‘dry’ conventionally prepared ILs was determined. Since the ILs are hygroscopic and can absorb water from the atmosphere, these studies are extended to identify any changes in solubility of the waste components in IL:water mixtures with varying water contents and in ILs obtained from the rapid synthesis method that are likely to contain higher levels of water than those prepared by conventional methods. Ionic liquids demonstrated selective solubility, a property that formed the basis of the extraction trials carried out in this research where the extent of extraction capability of the ILs was ascertained. These trials demonstrated that ILs can be a powerful tool for extraction and recovery of components from organic materials, where the ILs themselves can be recovered in high yield for recycle within a closed loop system. A major organic food-related waste stream is waste cooking oil which represents an attractive alternative feedstock for biodiesel production. A particular feature of waste cooking oils, however, is the elevated levels of free fatty acids that are produced during the frying process which reduce the effectiveness of the traditional transesterification process to produce biodiesel. To address this challenge, the research involved a two-step approach: (i) the identification of suitable ILs as extractants for fatty acids and as catalysts for esterification reactions on a model system; and (ii) the preparation of a simulated waste cooking oil, derived from pure palm oil, for trialling its conversion to fatty acid methyl esters (biodiesel) using an IL mix, as extractant and esterification catalyst. HPyrBr/SMIMHSO4 and HPyr/SPyrHSO4 were developed and found to exhibit both fatty acid extraction and esterification catalysis properties. Solubility testing of fatty acids and their methyl esters in the IL mix showed that the fatty acid extracting property and the ester separation mechanism of the IL mix were still preserved. In conclusion, as well as exploiting the properties of ILs in a dual reaction system, with a novel IL mix, a further benefit of the developed process is the ability for the first time to conduct the extraction of free fatty acids and their esteriification in a “one-pot” reactor. In all cases, the recovered IL and/or IL mix demonstrated the potential for its reuse within the closed loop process.