| China's oil dependence on foreign countries is up to 70%.Biomass is the only carbon-containing renewable resource that can be converted into liquid fuel.The preparation of liquid fuel by biomass is of great significance for the clean and efficient use of agricultural and forestry waste and the alleviation of petroleum resources'shortage.The fast pyrolysis of biomass is the most efficient and fast way to prepare bio-oil.However,the components of bio-oil are complex,in which the heavy component has a large molecular weight,high viscosity,poor fluidity and low conversion and utilization efficiency,therefore it can only be used as the low-quality product at present.The light component of bio-oil has a short carbon chain,and it is easy to break the connection bond and hydrogenate,so it can be used in various ways to produce high-quality oxygen-containing additives and aviation fuel.As a result,how to convert the heavy components of bio-oil into light components is the key to achieving high value utilization.Based on this,this paper puts forward the method that pretreatment of biomass to weaken chemical bonds,then broken-bond catalysts are used to improve the yield and quality of light bio-oil.The research focuses on the effects of solvent pretreatment on the surface characteristics and pyrolysis characteristics,preparation of breaking-bond catalysts,and catalytic pyrolysis of pretreated biomass to produce light bio-oil.The specific content and main conclusions are as follows:The effect of solvent pretreatment on the surface properties and pyrolysis characteristics were studied.A variety of organic and acid solvents were used to pretreat poplar sawdust and the most difficult component of biomass(lignin).The effects of pretreatment on the surface structure and functional group distribution were firstly studied.Then fast pyrolysis of pretreated biomass was carried out to produce oil,during which the effects of pretreatment on the distribution of pyrolysis products were further studied.The results showed that the effect of hydrochloric acid pretreatment was the best among all solvents.After pretreatment,the types of lignin functional groups remained unchanged,but the plane C-H deformation of aromatic rings,C=O stretching of primary alcohols and C-O stretching of guaiaceous rings decreased significantly.The methoxy groups increased,while the hydrocarbon impurities,fatty acetates,guaiacyl groups and syringyl groups decreased significantly.The bond energy of various chemical bonds was reduced,which is conducive to subsequent thermal breaking.After pretreatment,the yield of lignin fast pyrolysis liquids increased by 20.21%,and the total peak area of pyrolysis products(mostly light bio-oil components)measured by GC/MS increased by 44%.The total peak area of light components in bio-oil obtained by fast pyrolysis of pretreated poplar sawdust increased by 1.63 times.The breaking-bond catalysts were prepared and used in catalytic pyrolysis of biomass to prepare light bio-oil.Firstly,the catalytic properties of various metal oxides and natural catalysts were studied.Based on the results,various layered catalysts(Zn-Mg-Al,Ni-Mg-Al,Ca-Mg-Al,Fe-Mg-Al,Co-Mg-Al,etc.)were synthesized.The results showed that Zn-Mg-Al was most favorable for breaking bonds of heavy components in biomass pyrolysis,due to its layered structure and metal active sites.The peak area of high-quality products(high effective hydrogen-carbon ratio)increased significantly,and the peak area and selectivity of low-quality products(low effective hydrogen-carbon ratio)decreased significantly.CaO has the best effect among traditional breaking-bond catalysts,but the Zn-Mg-Al reduces the rate of coking deactivation due to layered structure and exhibits the better performance.Experimental study on the preparation of light bio-oil was conducted by catalytic pyrolysis of pretreated biomass.The effects of hydrochloric acid pretreatment on the product distribution during catalytic pyrolysis of poplar sawdust with Zn-Mg-Al catalyst were studied.The effects of catalytic pyrolysis operational parameters(pyrolysis temperature,material ratio)were investigated.Finally,the optimized process was applied to gramineous biomass to verify the universality of the process.The results showed that the yield of light components increased and the optimum temperature decreased after pretreatment.The maximum liquid product yield(59.25 wt%)was obtained at pyrolysis temperature of 450 ~oC with the Zn-Mg-Al ratio of 16.7%.Besides,the quality of light bio-oil was greatly improved.The pretreated gramineous biomass(rice stalks)was catalyzed under the optimized conditions.The results showed the liquid product yield increased by 7.6%compared with the direct pyrolysis of rice straw,and the quality of light bio-oil was also improved,which proved that the pretreatment method and the synthesized catalyst were applicable to gramineous biomass. |
PDF Full Text Request