| Lignite,as the typical low rank coal,is a kind of important carbon resource on earth.However,the utilization efficiency of lignite as primary energy is low and the utilization process commonly cause serious pollution to the environment due to several specific properties,such as high content of water and volatiles but low calorific value.On the other hand,lignite contains abundant natural structure units and has high chemical reactivity,making it possible to utilize lignite as non-energy resource.Therefore,exploring novel and value-added approaches of non-energy resource use of lignite becomes the realistic demand and an inevitable choice for the utilization of lignite and other low rank coals.Oxidative depolymerization is a potential way to realize clean and high value utilization of lignite.However,the depolymerized products are rather complex mixtures,and how to realize the effective utilization of depolymerized mixtures is a bottleneck problem that limits the utilization of lignite depolymerization.In this thesis,according to the characteristics of abundant acidic oxygen-containing functional groups in lignite or its depolymerized products,together with the coordination between acidic oxygen-containing functional groups and metal ions,new routes of using lignite and its depolymerized products were put forward,which using lignite or its depolymerized products as the organic ligand to construct metal ions-organic ligand composite catalyst without complex separation of lignite or its depolymerized products.Based on this research,it was found that the metal ions could selectively coordinate with different organic acid components in depolymerization products,and a new method of coordination separation of organic acids mediated by metal ions was proposed.The main conclusions of this thesis are as follows:（1）A novel and facile route was designed using raw lignite directly as robust organic ligands to construct Zr-based catalyst based on the interaction between Zr4+and the abundant oxygen-containing acidic functional groups in lignite.The selective hydrogenation of biomass-derived carbonyl compounds into alcohols was used as the model reaction to evaluate the performance of the catalyst.The structures of the catalyst were characterized by SEM-EDS,XRD,FTIR,Raman and TG,and both the preparation conditions of the catalyst and the reaction parameters were systematically investigated.The results verified that the constructed catalyst was efficient for the conversion of furfural.The furfural conversion,furfuryl alcohol yield,and the selectivity could reach 93.4%,81.0%,and 86.7%respectively under the optimized conditions.Compared with the similar catalysts,the reaction conditions of the prepared catalyst were more competitive.The results of catalyst stability showed that demineralization of lignite before preparing catalyst could improve the reusability of the catalyst.The proposed route was identified to be applicable for different low rank coals,such as lignite and long flame coal.The catalyst prepared using lignite was robustly effective for the conversion of various carbonyl compounds with different structures,indicating the broad universality for different substrates.This new strategy of constructing Zr-based catalyst may have potential applications in the value-added utilization of both low rank coal and the biomass resources,with the advantages of high efficiency of the catalyst,low cost of raw materials,and simple preparing process.（2）Both the content of the zirconium active component and the specific surfacearea of the catalyst prepared using raw lignite were relatively lower from the above research results,which limited the further improvement of the performance of the catalyst.In this chapter,the lignite was treated by oxidative depolymerization,and the obtained depolymerization products were directly used in the construction of different catalysts without complex separation.The lignite was depolymerized by ruthenium ion catalytic oxidation to obtain depolymerized products,which were rich in a variety of small molecule fatty acids and benzene carboxylic acids.Different kinds of catalysts,including zirconium-based hydrogenation catalyst,copper-based oxidation catalyst,and iron-based photocatalytic catalyst,were constructed by the coordination of different metal ions with depolymerization products to investigate the universality of the proposed catalyst construction route.The results showed that the proposed route using the depolymerized mixtures from lignite via RICO to construct catalysts was feasible.The prepared catalysts gave high efficiency for their corresponding reaction,including Zr-based catalyst for catalytic transfer hydrogenation of biomass-derived carbonyl compounds,Cu-based catalyst for selective oxidation of alcohols,and Fe-based catalyst for photocatalytic degradation of organic dye.The results of the characterization of the depolymerization product–zirconium catalyst showed that the content of zirconium and the specific surface area of the catalyst constructed from the lignite depolymerization product were higher than that of the lignite raw coal-zirconium catalyst,so its catalytic efficiency was higher.Further analysis showed that the contributions of different organic acid products to the catalyst were different.Some organic carboxylic acids,such as trimesic acid,contributed more significantly to the catalyst activity,while benzoic acid,fatty acid and some high value-added aromatic acids,such as benzoic acid,contributed less significantly to catalyst activity.The above results showed that the utilization idea of directly constructing catalyst with lignite depolymerization products was of great significance to the utilization of complex lignite depolymerization products,but different components in the depolymerization products had different contributions to catalyst activity.It is necessary to separate and utilize the depolymerized products in order to give full play to their high added value.（3）In order to further improve the utilization efficiency of depolymerization products,a new method of separating valuable organic acids（VOAs）from depolymerization products by the coordination between metal ions and VOAs was proposed.The technical route mainly included three steps,（i）metal ions selectively combined with organic acids to form metal ion-organic acid intermediate precipitation,（ii）the intermediate precipitation dissolution in HCl or Na OH solution,and（iii）metal ion recycling and reuse.Results showed that among the 11 metal ions investigated,most metal ions(Mn+)can selectively coordinate with VOAs in the depolymerization products to form M-VOAs intermediate precipitation.The VOAs were transferred from the aqueous phase to the solid intermediate precipitation,which could be dissolved in the Na OH solution,thus"releasing"organic acids from the precipitate species into the solution.Meanwhile,Mn+was recycled and reused in the form of M（OH）n.The types of metal ions,the amount of metal ions,the p H value of mother liquor and the coordination reaction temperature could be used to adjust the separation yield and selectivity of different organic acids.The reaction temperature of metal-induced separation method was low,closing to room temperature,and the green medium water was used as the solvent,which does not need to use organic solvent.Because of the advantages of high efficiency,facile regulation of separation selectivity and green process,this separation strategy had a potential application prospect in the effective and clean utilization of lignite depolymerized products. |
