| The plants can construct their fronds by absorbing the nitrogen and phosphorus from the eutrophicated water body, and adsorb heavy metals from the polluted water through biosorption process. However, after these processes, the pollutants are usually enriched in the plant biomass, and may cause secondary pollution problems if the pollutant-enriched biomass is mishandled. On the other hand, due to depletion of fossil energy, and the environmental and climate problems caused by the use of fossil energy, it urgently needs to recover energy and resource from the renewable and environmentally friendly biomass. As a mature and promising technique for the recovery of energy and resource from biomass, it will be great environmental and economical significance if the fast pyrolysis can be used for treating the polluted biomass.In this thesis, the enhanced removal of pollutants by biomass, as well as the migration, transformation, and distribution of pollutants during the fast pyrolysis of biomass were investigated systematically. The mechanism for the migration and transformation of the pollutants during biomass pyrolysis process was explored. Based on the above results, we developed two sustainable methods for the upgrading of bio-oil, and applied the biomass as raw materials to synthesize a series of functional carbon materials and explore their applications in the fields of environment, catalysis, and energy storage. The main contents and results of this thesis are as follows:1. Surface modification of the biomass to enhance the pollutant removal. A chemically modified Typha angustifolia biomass material with abundant carboxyl and amino groups was prepared using SOCl2-activated EDTA as a modification reagent. The results indicate that the chemical modified biomass exhibited significantly enhanced removal ability towards Pb in wastewater, and the maximum adsoption capacity reached263.9mg/g, much higher than that of the raw biomass (104.5mg/g). The main mechanisms involved in the Pb removal process included ion-exchange, complexation, and hydrogen binding interactions, among which the ion-exchange mainly occurred at a low pH, while the complexation, and hydrogen binding interactions contributed mainly at a high pH. 2. Migration and transformation of the pollutants in the fast pyrolysis of biomass as well as the related mechanism. The migration, transformation and distribution of Pb in the fast pyrolysis of Pb polluted biomass were investigated. During the whole pyrolysis process, when the temperature was increased from400to600℃, the Pb recovery efficiency exceeded98.8%. The main mechanism for this phenomenon is that during the pyrolysis process, the adsorbed Pb was transformed to PbO and metallic Pb, which could not volatilize and remained in the char phase.The migration and transformation of N and P in the fast pyrolysis of three typical N-and P-enriched wetland plants were studied. The main compositions of the obtained bio-oil included phenols, aldehydes, ketones, carboxylic acids, and nitrogen-containing heterocyclic compounds. In the pyrolysis process, a large amount of the organic N and P was converted to inorganic forms and remained in the biochar, which could be recovered by leaching. In average,76%of N and57%of P could be recovered in this case.The biomass and plastics of electronic waste were mixed in a certain ratio and co-pyrolyzed, and the fate of brominated flame retardants (BFRs) in the co-pyrolysis process was studied in detail. The mechanism for the transformation of BFRs was further investigated by the TG-FTIR-MS technique. The results show that The synergistic effects between the plastics and biomass can significantly improve the yield of bio-oil. As the mechanism analysis shows, the Br radicals formed in the pyrolysis process can be either captured by the organic species to form brominated hydrocarbons and release to the bio-oil or gas phases, or captured by the inorganic species and remained in the char phase.3. The upgrading of bio-oil and its mechanism. A green method for bio-oil upgrading at ambient pressure and temperature through in-situ hydrogenation by the zero-valent Zn was proposed. The results indicate that zero-valent Zn showed favorable reactivity in the complex bio-oil system, which ccould significantly improve the property of bio-oil, including decreased corrosivity, and increased heating value and stability. The formation mechanism of13newly formed compounds in the upgraded bio-oil involved the direct hydrogenation of aldehydes and ketones, esterification of alcohols and organic acids, and hydrogenation of the fragments of lignin.A new method for selectively improve the quality of bio-oil with Cu catalysis in the pyrolysis of Cu preloaded biomass was developed. The results indicate that the mono-aromatic compounds contents in the Cu catalytzed bio-oil were greatly higher than those in the non-catalyzed bio-oil. The main mechanism for this phenomenon is that the presence of Cu could promote the decomposition of lignin in the biomass, which minght produce various mono-aromatic compounds. After pyrolysis, more than90%of the preloaded Cu was enriched in the biochar phase, which could be easily recovered by a calcination method.4. Synthesis of functional carbon materials by the thermochemical methods using the biomass as raw materials. The waste sawdust biomass was used as adsorbent to adsorb MgCl2from seawater to obtain the MgCl2preloaded biomass, was then pyrolyzed to synthesize mesoporous carbon stabilized MgO NPs, which was further used for CO2capture. The maximum CO2capture capacity of the as-synthesized material was5.45mol/kg. The mechanism involved in the CO2capture process included physical adsorption and chemical interaction, among which the physical adsorption was weaken with the increase in temperature, while the chemical interaction contributed mainly to the CO2capture, which included hydrogen binding and the reaction between CO2and MgO.A magnetic porous solid acid material was synthesized by pyrolysis and then sulfonation of FeCl3preloaded biomass. The as-synthesized material was used as a catalyst for the organic reactions. The results indicate that the presence of FeCl3could catalyze the formation of the porous structure in the pyrolysis process. The magnetic solid acid had a high acid strength and large surface area, which exhibited a high catalytic activity, favorable separability and cycle stability.The nitrogen-doped porous carbon materials were synthesized from an N-enriched wetland plant biomass by a simple fast pyrolysis and KOH activated method. The as-synthesized materials were used as electrode materials for supercapacitor, and their energy storage performance was evaluated. The as-synthesized materials had porous structure with a surface area higher than3000m2/g, and exhibited favorable performance as a supercapacitor with a high capacity (257F/g), large energy and power density (19.0Wh/kg), and could be reused6,000cycles without significant loss of the capacity. |
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