| Environmental concerns and the security of energy supply have boosted interestin the development of alternatives for fossil based energy carriers and chemicals.Biomass has been considered as a promising resource because it is abundantlyavailable and in principle CO2neutral. Biomass can be converted to liquid bio-oilwith high energy density by fast pyrolysis technology. However, the bio-oil is notdirectly suitable as a bio-fuel for internal combustion engines because it containslarge amounts of water and corrosive organic acids and shows limited storagestability. Therefore, bio-oil upgrading by either physical or chemical methods isrequired. To increase the economic attractiveness, bio-oil upgrading processes toobtain fuel and valuable chemicals are studied in this research.Firstly, hydrogenation of bio-oil was carried out in this study. Afterhydrogenation, liquid product consisting of an aqueous phase and an oil phase wasgenerated, and its properties such as water content, pH value, higher heating value(HHV) and component and so on were characterized. Results showed that the watercontent of oil phase was much lower and its pH value, higher heating value andstability were improved, which became much more suitable as fuel. In contrastorganic compounds in the aqueous phase became much less, mainly carboxylicacids. So this part was used for chemical recovery in the following study.Acetic acid recovery from aqueous phase was carried out by using reactiveextraction method. Factors affecting the extraction efficiency, such as extractants,diluents, extractant concentration and initial concentration of acetic acid wereinvestigated to optimize extraction conditions. Results showed that an acetic acidextraction efficiency of84.4%could be obtained using50~60vol.%tri-n-octylamine diluted in2-ethyl-hexanol as the extractant system and the volumeratio of extractant system and aqueous phase was1. Furthermore, the COD of theaqueous phase before and after reactive extraction was measured. A high COD removal efficiency of77.5%was obtained, which benefits for reducing the cost ofsubsequent treatment.Esterification is also an effective method for recovering acetic acid andpurification of water. Since esterification is a typical reversible reaction and theconcentration of acetic acid in the aqueous phase is really low, anesterification-extraction method is proposed to improve the reaction efficiency. Inthis method adding organic extractants to the esterification system leads to the ethylacetate product transfer into the organic phase, thereby promote the esterificationequilibrium shift to formation of ester. Effects of ultrasound, organic solvent, aceticacid to ethanol molar ratio, and reuse of organic solvent on the esterificationefficiency were firstly studied using dilute acetic acid aqueous solution as simulated.The results showed that the ultrasonic accelerated the esterification reaction rate, andtoluenewas more suitable as organic solvent to promote esterification rate.Moreover, esterification efficiency significantly increased by increasing the amountof organic solvent and ethanol. Then, the performance of this method for acetic acidesterification in aqueous phase of bio-oil hydrogenation was investigated under theoptimum conditions, and a considerable esterification efficiency of86.5%wasachieved, while the aqueous solution was purified. Results indicate thatesterification-extraction method can effectively improve the esterification efficiencyand show great practical prospect.Catalytic hydrogenation of bio-oil not only improved the quality of the oilphase, but also enriched acetic acid in the aqueous phase.Both reactive extractionand esterification-extraction method can simultaneouseffectively recover aceticacidandpurify the water preliminarily. This study issignificant for improving theutilization and economic benefits of biomass. |
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