Physicochemical property analysis and structural characterization of bio-based polyol prepared form microalgae oil

Abstract: In order to cope with the resource crisis and environmental pollution that caused by the rapidly depletion of non-renewable petroleum resources, as well as to achieve the efficient and high value utilization of inedible green renewable oils were investigated. Bio-based polyols with different structures were prepared from microalgae oil, and the methods of epoxidation-ring opening and hydroformylation-hydroreduction were used to obtain the goal products. Physical and chemical properties of the raw materials and the resulted products were analyzed by determining the critical indexes including iodine value, acid value, oxirane oxygen content and hydroxyl value, and theoretical double bond content, theoretical oxirane oxygen content, theoretical hydroxyl value, conversion rate and selectivity. Structure of the raw material and the resulted products were characterized by gas chromatography-mass spectrometry, gel permeation chromatography, Fourier transform inferred spectrometry, and nuclear paramagnetic resonance. Results of the physical and chemical analysis and the structure characterization demonstrated that the main fatty acid composition of microalgae oil was oleic acid with high content of 91.10%, the iodine value of microalgae oil was 88.46 g /100g, and the theoretical double bond content of microalgae oil was 0.34 mol/100g. The iodine value of polyols obtained via epoxidation-ring opening method decreased to 0.62 g /100 g, the hydroxyl value was 150.35 mg /g, the conversion rate of microalgae oil was 99.30%, the selectivity of resulted target polyol was 86.74%, and the secondary hydroxyl group was introduced into the double bonds of triacylglycerol in microalgae oil. In addition, the goal polyol quality can be effectively promoted by immediately removing the water that generated in the epoxy reaction process and selecting the appropriate amount of alcohol in the ring opening reaction process. The iodine value of polyols obtained via hydroformylation-hydroreduction method decreased to 2.12 g/100g, the hydroxyl value was 166.29 mg/g, the conversion rate of microalgae oil was 97.60%, the selectivity of resulted target polyol was 95.83% and the primary hydroxyl group was introduced into the double bonds of triacylglycerol in microalgae oil. Due to the heterogeneous catalysts and inexpensive solvents were adopted both in the hydroformylation process and hydroreduction process, the resulted polyol can be easily separated by filtering to remove the catalyst, and the solvent can be recovered using vacuum distillation. Furthermore, the hydroformylation-hydroreduction method showed small side effects which make it easy to control the quality of the goal polyol. Both methods of epoxidation-ring opening method and hydroformylation-hydroreduction were given high raw material utilization and good reaction selectivity, more importantly, the physical and chemical properties of polyols could availably be evaluated through the simple and easy methods of the critical index determination and theoretical calculation, and the instrumental analysis could be used to quickly monitor the reaction progress, assure the product quality, identify the product quality problem, and broaden the utilizing scope of product. These two methods would be perfect economical technical routes and have excellent industrial application prospects for bio-based polyols prepared from oil. The results provide scientific and reliable data basis for the in-depth research of bio-based polyols prepared from oil, while provide technical support for the industrial application.