Clean And Highly Efficient Preparation Of Furfural From Bagasse And Efficient Utilization Of Furfural Residue

Furfural is the important furan compounds,which could be produced from pentose?xylose and arabinose?or pentose-rich biomass.Furfural possessing high chemical activity,can be further converted into a variety of value-added products and biofuels,which are widely used in plastics,medicine,pesticides,energy and other industries.At present,there are still some problems in large-scale production of furfural in industry,such as low yield of furfural,inefficient utilization of furfural residue,and equipment corrosion and serious environmental pollution caused by liquid acid.Multi-co-production technology of biomass plays a key role to build a stable,economic and clean biomass bio-refinery,and it also is a significant approach to breakthrough resource and environmental constraint.Based on this point,in this thesis,the strategy for clean and highly efficient preparation of furfural and high-value utilization of furfural residue were proposed by catalytic technology combined with pulping technology or carbonization method.In the furfural preparation stage,hydrothermal treatment reduced by solid catalyst in one-step or two-step process was applied to convert xylan-type hemicellulose in bagasse into furfural.For the industrial furfural residue utilization,catalytic technology,cooking technology and carbonization method were conducted to treat industrial furfural residue for production of high value-added products such as platform compounds,dissolving pulp,nanostructured material,and carbon-based catalyst.Accordingly,existing raw materials achieved the high-efficient utilization,and the optimization of economic benefits was simultaneously realized.The details were as follows.1.Hydrothermal catalysis of bagasse continuously induced by solid acids for coproduction of furfural and levulinic acidIn order to overcome the difficulty of separation solid acid catalysts from solid raw materials,a two-step process was developed to produce furfural and levulinic acid?LA?using the continuous hydrothermal treatment of bagasse induced by the SO₄^2-/Sn-MMT?Montmorillonite?solid acid.In this work,response surface method was used to study the effects of various factors on furfural yield.The results showed that solid acid catalysts(SO₄^2-/Sn-MMT)played a key role in hydrothermal reaction and the highest yield of furfural was achieved up to 88.1%?170°C,2.4 h?in the NaCl/DCM?Sodium chloride/Dichloromethane?biphasic system in the first stage.In the second step,the treated residue was further hydrothermally treated for producing LA by the continuous use of solid acids,and the yield of levulinic acid?LA?was 62.1%at 180°C for 3 h.In addition,Fourier transform infrared spectroscopy?FTIR?,X–ray diffraction analysis?XRD?,Thermogravimetric analysis?TGA?and Scanning electron micrograph?SEM?analysis of bagasse and solid residue after one-step or two-step treatments further confirmed that hemicellulose and cellulose of bagasse were selectively fractionated and efficiently transformed into furfural and levulinic acid.This study will provide a new route for selective fractionation utilization of hemicellulose and cellulose in bagasse.2.Two-step process for green and efficient preparation of furfural from bagasse with coproduction of dissolving pulpThe strategy of coproduction of furfural and dissolved pulp from bagasse was developed by catalysis technology combined with pulping technology.Firstly,organic acid?oxalic acid?was used to selectively dissolve and hydrolyze hemicellulose in bagasse to xylose-rich hydrolysate.Then the hydrolysate was catalyzed into furfural by iron phosphate which was insoluble in low-temperature water.Subsequently,furfural residue was treated with green recyclable p-benzoic acid followed by bleaching treatment with hydrogen peroxide,in which solid residue finally obtained could be applied for dissolving pulp production.The effects of organic acid pretreatment of bagasse and ferric phosphate catalyzed hydrolysate on the yield of pentose and furfural were studied,respectively.The catalytic mechanism of iron phospharte was discussed as well as the recovery and recycling performances.The effects of p-benzoic acid and hydrogen peroxide on the composition and properties of residue before and after reaction were investigated by National Renewable Energy Laboratories?NREL?,FTIR,XRD,TGA and SEM.The results showed that 82.6%xylose hydrolysate was obtained by treating bagasse with 0.15 M oxalic acid for 120 min at 140 ^oC.Under hydrothermal conditions of 190 ^oC–120 min,the highest yield of 88.7%furfural was obtained by catalyzing xylose-rich hydrolysate using ferric phosphate as the catalysts.The experiments of five-time recycles showed that this catalyst exhibited excellent stability and catalytic performances.The content of lignin and?-cellulose in furfural residue treated with p-toluene sulfonic acid decreased to 9.86%and increased to 82.3%,respectively,at 90 ^oC for 20 min.After bleaching with hydrogen peroxide,the content of lignin and?-cellulose decreased to 2%and increased to 94.7%.In this study,hemicellulose and cellulose in bagasse were converted into furfural and dissolving pulp,respectively,by pretreatment and catalysis-coupled-pulping technology,which provided a new insight for lignocellulose biomass refining with hemicellulose-priority conversion.3.Lignin isolated from furfural residue by alkaline cooking technologyFor the current situation of difficult utilization of industrial furfural residue,lignin in furfural residue was extracted by alkaline cooking,and the effects of different alkali extraction conditions on the structure of lignin obtained were studied.The effects of different alkali treatment conditions on the composition and chemical properties of the solid residue were characterized by NREL,¹³C NMR and Infrared total reflection?ATR?.Results showed that lignin obtained from furfural residue by alkali extraction contained abundant guaiacyl?G?,syringyl?S?and p-hydroxyphenyl?H?structural units,in which G-type lignin structural units accounted for the main proportion.More importantly,the phenolic hydroxyl groups were rich in the lignin sample,and the highest content of hydroxyl groups in the lignin sample was 4.02mM/g under the cooking condition?135 ^oC–0.35 M?.Lignin obtained displayed good antioxidant properties.The results also showed that the content of cellulose in the solid residue decreased,and the content of lignin increased significantly.This phenomenon is attributed to the fact that alkali extraction had an important effect on the chemical structure of cellulose in solid residues,resulting in side reaction,consequently yielding a solid substance that is insoluble in water.This study will offer the important information for the modern pulp and paper industry of furfural co-production.4.Nanomateirals preparation from furfural residueIndustrial furfural residue is difficult to be used because of the high degree of acidification,as inspired by the pulping technology,a feasible method was proposed to separate cellulose and lignin from furfural residue by treatment of formic acid-hydrogen peroxide mixture?FA–H₂O₂?.Three kinds of products including lignin,nanoscale cellulose and nanoscale lignin were obtained by ultrasonic,dilution and high-speed centrifugation technologies.The effects of formic acid-hydrogen peroxide treatment conditions were discussed on the properties of lignin,nano-scale cellulose and lignin,and the structures of these products were characterized and analyzed.Results showed that this FA–H₂O₂ system was very effective in extracting lignin from furfural residue.When the furfural residue,formic acid and hydrogen peroxide were 5 g,40 mL and 16 mL,respectively,the lignin content in the treated residue reached to the lowest value?0.8%?and the corresponding cellulose content was 88.0%.The structure of lignin obtained by the dilution-precipitation procedure was mainly p-hydroxyphenyl?H?with the molecular weight of 1093 g/moL.The nanoscale lignin particles obtained from supernatant fraction by centrifugal technology displayed an oblate sphere with in the transverse size range of 332⁵11 nm and a thickness of 2¹0 nm.Prepared nanocellulose obtained by ultrasonic cell crusher had a width of 20⁵0 nm,a length of500¹000 nm,an aspect ratio of 2.5⁵0,also existed a Zeta potential of-35 mV^-45 mV and a transmittance of 65%⁸5%.This method opens a new window for the application of furfural residue in the field of nanomaterials.5.Carbon-based catalyst from furfural residue and its catalysis performanceIndustrial furfural residue contains two main components?cellulose and lignin?.In view of characteristic of high carbon content in furfural residue,a feasible approach was developed to prepare carbon-based solid catalysts?CSC?from furfural residue by activation and carbonization for the hydrolysis of microcrystalline cellulose?MCC?into glucose.The influence of activation and carbonization was discussed on the properties of carbon-based catalyst.And the MCC hydrolysis via prepared carbon-based catalyst was investigated for glucose production.The carbon-based catalysts possessed the structure of mesoporous carbon with weak acidic carboxylic and phenolic groups.The 65.2%and 83.9%yields of glucose were achieved at 200°C for 50 min using mixed ball milling of MCC and CSC and subsequently hydrothermal treatment in pure water and the 0.012 wt%HCl solution system,respectively.In addition,the activation energy of mixed ball milling?59.0 kJ/mol?was significantly lower than that of single ball milling?89.7 kJ/mol?and non-ball milling?158.7kJ/mol?for the MCC hydrolysis,indicating that the activation energy was reduced by mixing ball milling of MCC and the CSC catalyst.This study will give the important information for the cellulose hydrolysis into glucose via solid acids.Accordingly,a new and feasible route of lignocellulosic biomass bio-refinery was developed based on hemicellulose-preferred conversion to furfural in this thesis.By catalysis technology coupled with pulping method or carbonization method,hemicellulose in lignocellulose was firstly converted into furfural by one or two steps,and the solid residue after reaction as raw materials was further transformed into chemicals and materials,such as levulinic acid,dissolving pulp,nanocellulose,nanolignin,lignin and carbon-based catalyst.Consequently,the highly efficient utilization of lignocellulose biomass could be achieved.This research will provide important technical support for the sustainable development of furfural industry.