Research On The Performance Of Catalytic Fast Pyrolysis Of Lignocellulosic Biomass And Its Phenolic Derivatives By Composite Meso-structured Zeolite

Lignocellulosic biomass is abundant as a renewable energy source and consist of a large number of natural aromatic ring structures.Through the thermo-chemical method,coupled with pyrolysis and catalytic cracking pathways,these materials can be converted into aromatic hydrocarbon products in one step with a high processing rate.Aiming at the scientific problems in the research,the design and synthesis of zeolite catalysts with composite mesopore structure were carried out,and its catalytic performance in the routes of catalytic fast pyrolysis of lignin and catalytic co-cracking phenolic bio-oil with ethanol was investigated.In view of the disadvantages of the conventional hierarchical zeolites as mass loss during preparation and its being hard to control the mesopores generation process,two series of novel micro-mesostructured composite zeolites were constructed by re-deposition and recrystallization method,both consisting an inner hierarchical core and an outer meso-shell.The first method was based on the strong alkaline etching operation of hierarchical sample.Through a redeposition process under mild conditions,the dissolved silicon and aluminum species reassembled into an amorphous mesoporous shell,coated on the surface of hierarchical core.The second method used weak-base ammonia hydrothermal method as the desilication step.By controlling the etching degree with adjusting the concentration of added organic alkali,and using hydrothermal method to recrystallize the dissolved species,an order mesolayer and ink-shape inner hierarchical pores were achieved on zeolites with micron and nano particle sizes.For three different kinds of mesoporous ZSM-5 zeolites(core-shell,hierarchical,first type composite pores),the textural properties were compared in detail,and used to produce aromatics by catalytic fast pyrolysis(CFP)of cellulolytic enzyme lignin(CEL).The structural parameters were adopted to analyze the relationship between mesopores distribution and catalytic performance,revealing the significant effect of equivalent mesopore size.Among them,a micro-mesostructured composite zeolite(ZMA)with internal hierarchical pores and ununiform mesolayer shell was prepared by self-assembly under mild conditions.ZMA had a suitable mesostructure,of which the interconnected mesochannels improved the accessibility of inner acidic sites.Also its moderate equivalent pore size maintained a certain shape-selectivity to suppress PAHs formation.It was further shown that the applicable catalyst to lignin ratio(C/L)ranges differed with various mesostructures,as ZMA and hierarchical samples were suitable for higher(in-situ CFP)and lower ratio(high concentration of phenolic reactants),respectively.A variety of modification and structural modulation methods were then carried out on the first type of composite mesostructure,and the corresponding catalytic pyrolysis performance of the CEL was analyzed.For the optimization of balance between aromatics yield and MAHs selectivity,it was found that the concentration of 0.2M NaOH is the ideal etching extend;the performance of physical mixing of the inner core and the mesopore zeolite was inferior to the composite structure,referring to the coupling effect of internal and external mesopores in the hierarchical composite structure;for the composite sample CZM,bimetallic loading of 5wt% Ni and 2.5wt% Fe had the highest MAHs selectivity and deoxygenation efficiency.The catalytic performance of hierarchical and first-type composite zeolite on the CFP of industrial lignin residues,Kraft Lignin(KL)and Pyrolytic Lignin(PL),had been investigated.Interestingly,the hierarchical sample was more suitable for the case of higher concentration of primary pyrolysis products as CFP of PL,and it was found that PL could produce aromatic hydrocarbons in high yields.While the mesoporous composite zeolite possessed better PAHs suppressing capability,and was suitable for low reactants concentration and high oxygen content,such as KL CFP.These results were compared with poplar sawdust as actual biomass,and mesoporous samples were both highly-efficient catalysts.The mesopore shape characteristics of zeolites also have a great impact on the conversion of biomass-derived heavy components.Based on the versatile ammonia-hydrothermal method,the main target products of phenolic bio-oil co-cracking of the nano-sized second-type composite pore zeolites were investigated,along with structural parameters and acidity properties of the corresponding catalysts.Nanoparticle sizes can effectively increase the cracking performance,especially promoting methoxyl removal.By introducing mesopores into ZSM-5,the co-cracking performance was altered significantly and no longer had good correlation with the concentration of acid sites.The topological shape and position of mesopores had a bigger effect,and the ordered mesopores on the outer surface along with internal mesopores with wide openings were more favorable than hollow mesopores inside with narrow openings.This tendency towards mesopore morphology can be quantified by several structural parameters.Between three kinds of mesostructure distribution,the core–shell ZSM-5 showed optimal performance with the highest BTEX yield and deoxygenation efficiency,which could be attributed to that its multilevel hierarchical mesostructure improved the diffusion of reactants and intermediates,and its synergistic reaction function.Finally,in preparation for the upcoming coupling of catalytic fast pyrolysis and bio-oil cracking routes,a continuous feed reactor for ex-situ CFP had been designed and built for the performance tests of subsequent catalytic systems such as composite mesostructured catalysts.