Preparation Of Functional Lignin Modified Porous Materials And Their Adsorption And Catalytic Performance

Lignin has attracted increasing attention by researchers due to its natural advantages of low price and renewable,as well as its chemical characteristics of special aromatic structure,abundant functional groups,easy functionalization and up to 60%carbon content.Based on these characteristics,lignin has become an attractive functional polymer raw material,which can be modified through hydroxymethylation,amination,sulfonation,carbonization,and graft copolymerization to obtain high value-added functional composites.Among these materials,functionalized porous materials have good application prospects in the fields of pollutant adsorption and catalytic conversion of renewable energy ethanol.However,the problems about tenacity of lignin separation,diversity with complex structure,low application matching degree and low added value hindered its functional application.How to efficiently separate lignin and use its structural and functional groups to develop high value-added products and orientate the material application is the key to improve the high-value application of lignin.Therefore,this paper focuses on the high value-added utilization of lignin,and a series of studies on the application of functional lignin porous materials for environmental adsorption and ethanol catalytic conversion were carried out.So as to achieve efficient matching from raw material acquisition to material synthesis and directional application.Meanwhile,the synergistic effect of lignin in materials was analyzed by various characterization methods and performance tests,and the mechanism of high efficiency adsorption or catalysis was revealed,which opened a new way for high value utilization of lignin.The main research contents and results are as follows:(1)Lignin was extracted by organic solvent method,alkali extraction and acid precipitation method,Klason method and molten salt method,respectively.The effects of different extraction methods on the structure and properties of lignin were analyzed through characterization.It was found that the structure,molecular force,and hydrophobicity of lignin extracted by different methods were different.The organic solvent lignin(OL)was relatively green and mild,so that more structural units and active groups of lignin were preserved,which is conducive to further modification or functionalization.Additionally,the OL and commercial lignin were analyzed and compared.It was found that lignin(dealkaline)not only has rich active functional groups with good thermal stability,but also has less ash content after pyrolysis carbonization and availability of raw materials.Therefore,it is considered to be used as carbon source to prepare carbon-based/modified catalysts.Lignin from different methods and sources has great differences in structure and properties,so the background of raw material cost,physicochemical properties,and synthesis technology should be fully considered in the actual utilization process to efficient matching application.(2)OL as a green and highly active raw material was used to prepare lignin-based copolymers(LCPs)precursor by solution polymerization.Then the in-situ Friedel-Crafts reaction was performed the precursor to obtain lignin-based hyper-cross-linked polymers(LHCPs)with a three-dimensional hierarchical porous.The addition of OL could increase the specific surface area(SBET)from 854.78 m2/g to 1499.56 m2/g,and the total pore volume(Vtotal)from 0.71 m3/g to 2.07 m3/g.Moreover,lignin could effectively regulate the porosity and polarity of the hyper-cross-linked polymers.LHCPs were first time used for iodine capture research.LHCP-2 adsorbed 253 wt%iodine vapors at 348 K and 1 bar,and adsorption performance was stable above 85%after five regeneration cycles.At the same time,the mechanism of iodine adsorption was explored.The efficient capture of iodine by LHCPs was due to the high specific surface area,hierarchical pore structure,abundant O-containing groups(-C=O and-OH)of lignin.Among them,the strong interaction between iodine and lone pair of electrons,and π-π aromatic structures form the driving force of iodine adsorption.(3)OL as an additive to modified hyper-cross-linked porous resins by suspension polymerization,which obtained lignin modified hyper-cross-linked porous resins(LMHCRs)with adjustable polarity and applied to p-nitrophenol(PNP)adsorption.The addition of lignin made the pore size distribution of the polymers more concentrated,and the hydrophilicity of the polymers was improved.With the increase of lignin addition,the specific surface area(SBET),micro pore surface area(Smicro)and micro pore volume(Vmicro)of the polymer decreased,indicating that the addition of lignin in the suspension copolymerization reaction was not conducive to the formation of micropores.However,the adsorption capacity of LMHCR-2 on PNP was significantly higher than that of HCR-0 without lignin.The maximum adsorption capacity of LMHCR-2 reached 492.1 mg/g,which was increased by 68%.Moreover,the adsorption rate was fast,and the regeneration capacity and recycling performance were good.In addition,LMHCR-2 adsorbed dyes with different molecular weights.It was found that the adsorption capacity of LMHCR-2 decreased with the increase of the molecular weight of the dye,indicating that LMHCR-2 had selective adsorption on small molecular dyes.Simultaneously,the analysis of structure-activity relationship indicated that the micropore filling mechanism,abundant oxygen-containing functional groups of lignin and π-π superposition were conducive to the adsorption of small aromatic molecules(PNP).And the adsorption isotherm and adsorption kinetics analysis showed that PNP adsorption process was more consistent with single-layer adsorption,which was mainly chemical adsorption.(4)The polymerization methods and forms of lignin based porous materials are various.To sufficiently develop the effective matching between materials and applications,iodine,organic dyes and CO2 were adsorbed by LHCPs and LMHCRs,which prepared by solution polymerization and suspension polymerization method respectively.The LHCPs prepared by solution polymerization had a multistage pore structure of micropore,mesopore and macropore,which was suitable for iodine adsorption and removal of dyes with relatively large molecular size(such as rhodamine B).However,the LMHCRs prepared by suspension polymerization was mainly microporous with a small amount of mesopores,which was suitable for the removal of small molecular dyes(such as PNP)and the capture of CO2 or other gases.This study will provide important guidance for the preparation of lignin hyper-cross-linked porous materials and efficient matching of directional applications.(5)A series of porous materials modified with lignin-derived carbon were prepared by impregnation-coupled heat treatment and applied to ethanol selective conversion to butadiene.In addition,the structure-activity relationship of the catalyst was revealed by various characterization methods.Lignin-derived carbon can effectively adjust the acid-base properties of ZnZr/SiO2.And 1%L-ZnZr/SiO2(L=Lignin)has excellent catalytic performance in the conversion of ethanol to butadiene due to its suitable acid-base properties.The conversion of ethanol and the selectivity of butadiene are 98.4%,and 55.5%respectively at 400℃ and 0.77 h-1.Meanwhile,it be provided with excellent catalytic stability.Besides,the results of temperature programmed ethanol surface reaction showed that the aldol condensation reaction is the decisive step for ethanol conversion to butadiene,which provides theoretical basis and new ideas for the development of efficient multifunctional catalysts for ethanol to butadiene.