Producing renewable chemicals from fishery waste: chitin, chitosan and the monomers

Omari, Khaled Walid Baker (2012) Producing renewable chemicals from fishery waste: chitin, chitosan and the monomers. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Chitin, chitosan, and their monomers were investigated as renewable feedstocks to produce useful chemicals. These biopolymers are readily available, cheap, non-toxic, and environmentally benign. They are produced, degraded and reabsorbed in nature. They could in part replace depleting resources, such as fossil fuels, in useful chemicals production. To this end, microwave heating, catalysts and additives have been investigated. Factorial designs (FDs) were used as an effective approach to optimise the reaction conditions. Reaction products obtained were extracted using ethyl acetate and their amounts were determined using GC-MS. Although these biopolymers are difficult to solubilise, useful products were obtained in water under the reaction conditions described herein. Levulinic acid (LA) and 5-hydroxymethylfurfural (5-HMF) were produced from chitosan using SnCI₄5H₂O which can be handled with ease and is a relatively inexpensive reagent. The medium for this reaction (water) is non-toxic, nonflammable, and readily available at low cost. The chitosan reaction mixture was heated to 200℃ under microwave irradiation for 30 min in a closed vessel. Two different reaction concentrations were tested; the "concentrated reaction" yielded 23.9 wt% LA, and the "diluted reaction" yielded 10.0 wt% 5-HMF. Each reaction has a high selectivity for the desired product; chitin was also able to produce LA under the concentrated reaction conditions (12.7 wt%), This proof of concept study showed that amino-saccharides can be used as feedstocks for levulinic acid and 5-hydroxymethylfurfural typically obtained from cellulosic biomass. It was discovered that a nitrogen containing compound 3-acetamido5-acetylfuran (3A5AF), could also be produced from chitin and chitosan in small amounts. However, by using N-acetylglucosamine (NAG) instead of chitin, a higher % yield of 3A5AF could be obtained, possibly due to limitations in the depolymerisation process of chitin. The transformation of AG was dependent on the supplier of this amino-sugar and it was discovered that B- and CI-containing impurities in one source were likely aiding the conversion process. Therefore, AG was reacted in the presence of two additives: NaCI and B(OH)₃. After solvent-screening, the reaction was optimized in dimethylacetamide (DMA). The reaction mixture was heated using microwave irradiation to 220℃ for 15 min. 3A5AF production was quantified using GC-MS. The % yield of3A5AF was determined to be ca 58. This study showed that this compound could potentially be produced cheaply and is a potential renewable feedstock for other N-containing molecules e.g. proximicins A, B and C (antibiotic and antitumor drugs). As an alternative to this method, a procedure was developed in ionic liquids (ILs) to produce 3A5AF. 3A5AF could be obtained in up to 60% yield by heating AG in the presence of NaCI and B(OH)₃. In summary, the research described in this thesis demonstrates the potential of fishery waste to produce valuable chemicals (LA, 5-HMF. and 3A5AF). Mechanisms of product formation are also proposed and discussed.

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