Mechanism Of Directional Liquefaction Of Lignocellulosic Biomass And Valorized Upgrading Conversion Of Liquefied Products

In China,abundant biomass energy is carbon neutral and not fully utilized.With increasing fuel demands and growing concern for the effects of greenhouse gas emissions from fossil fuels,developing renewable and sustainable chemical and fuel production methods is imperative.Lignocellulosic biomass is one of the most promising renewable energy sources for the sustainable production of high added-value chemicals and fuels.Converting solid biomass into liquid products can significantly increase the feasibility of transportation and density of energy.In recent years,a great deal of efforts has been directed at developing a simple and effective process to produce high added-value chemicals from lignocellulosic biomass.Thermochemical conversion of lignocellulosic biomass into renewable chemicals has attracted extensive attention because of increasing public attention on environmental protection and growing demand for sustainable biofuels and chemicals.This research focuses on the fundamental mechanisms and methods for stabilization of the intermedium products and their predictable conversion mechanisms during the directional liquefaction of lignocellulosic biomass.The formation pathway and mechanism of levulinic acid esters from methyl glycoside will be studied for the possible application as fuel additives.Three phenolic compounds fractions were hydrogenated and deoxygenated to cyclohexanes using bifunctional catalysts via in situ hydrodeoxygenation.The main contents are as follows:1.Liquefaction of lignocellulosic biomass using concentrated sulfuric acid as catalyst,and nethanol or methanol-glycerol complex as solvent were investigated.The results show that the products from liquefaction of lignocellulosic biomass shaving are mixture of phenolics and methyl glycoside.The mass balance of the liquefaction process was investigated at the same time.Liquefied products can be further separated into a variety of high value-added products such as phenolics and glycosidics.With the only methanol solvent,the main components of liquefied products are glycosidic compounds,which content is up to 83.38%,phenolic products from fractionation of liquefied product were mainly composed of 4-ethyl-2-methoxyphenol,eugenol and 3,4-dimethoxyphenol,which accounting for about 65.79%.With methanol-glycerol co-solvent effect,glycosidics mainly contains about 41.81%of methyl glycosides,and47.27%of unreacted glycerin and glycerin polymers,and phenolics phase mainly contains phenols and glycerol,the content of glycerin and its polymers is 38.04%.Based on the molecular structure of lingo-cellulosic materials,cellulose and hemicellulose can be transformed to alkyl glycoside under the catalysis of acid through compressed conditions.Due to electronic effects of phenolic hydroxyl and methoxy groups,guaiacyl units in lignin can lead to C—C bond cleavage to form guaiacol,phenol and other phenolic compounds.2.Converting lignocellulosic biomass into high-quality chemicals and fuels can significantly increase the feasibility of transportation and density of energy.In this study,we developed a one-pot integrated catalytic conversion strategy,which simultaneously converted both the cellulose and hemicellulose fractions from lignocellulosic biomass into high value-added chemicals?methyl levulinate?.With a traditional solvent,only the C6 sugar substrates in cellulose and in hemicelluloses could be converted into levulinic acid or levulinic esters.In this strategy,C6 and C5 sugars in the cellulose and hemicelluloses were simultaneously converted into methyl levulinate?MLA?in the one-pot process using dimethoxymethane and methanol as composite solvents.Methanol as a reactant can promote the alcoholysis of holocellulose in biomass and suppress both the polymerization of the byproducts?sugars/furans?and the Aldol condensation of levulinic acid/ester.Dimethoxymethane acted as an electrophile to transform furfural into 5-hydroxymethylfurfual?HMF?.When methanol and dimethoxymethane were used as the co-solvent,a 40.98%methyl levulinate yield could be obtained from bamboo.The overall reaction pathways for the simultaneous catalytic conversion of hemicellulose and cellulose into methyl levulinate with acid catalysis and a co-solvent were proposed based on the results of the GC-MS analysis.The results suggested that this simultaneous catalytic conversion of biomass is an effective method that can produce high yields of value-added chemical?MLA?from waste lignocellulosic biomass.3.To explore an effective method for the comprehensive utilization of biomass,a simple“directional liquefaction”process was introduced to produce phenolic compounds from waste biomass.The effects of process parameters?catalyst dosage,liquefaction temperature and time?on the yield and composition of directional liquefied products were investigated.The liquefied products were separated into liquefied liquid and solid products.The highest phenolics content can be achieved?63 wt%?in the liquefied liquid products.Using stepwise extraction,phenolics were largely separated into three phenolic compounds fractions.From GC-MS analysis,three phenolics fractions were mainly comprised of aromatic derivatives such as 2,4-dimethoxy phenol,3-methoxy-4-hydroxy benzaldehyde,3-methoxy-4-hydroxy phenyl acetate,and 3,5-dimethoxy-4-methylphenol.They all had good solubility in conventional organic solvents such as methanol and acetone.In general,most of the hemicellulose and non-crystalline of cellulose were decomposed into glycosides.Lignin was transformed into phenolic compounds using the directional liquefaction and microwave-assisted liquefaction process.The combination of directional liquefaction,stepwise fractionation,and chemical-purified treatment was effective to produce renewable phenolic compounds.4.Conventional liquefaction of waste lignocellulosic biomass produces many complex and unpredictable mixtures with unstable structures.These liquefied mixtures may bring some technical and economic barriers during the consecutive upgrading process.Upgrading the quality of liquefied products is an essential process before high added-value utilization of liquefied waste lignocellulosic biomass can be achieved.An effective“directional liquefaction”process,and stepwise process with precipitation and extraction from the liquefied products are introduced for producing two categories of platform chemicals:aromatic derivatives and monosaccharide derivatives.The saccharide derivatives generated from cellulose and hemicellulose,contained five-carbon and six-carbon saccharide derivatives.These monosaccharide derivatives,such as methyl glucoside and methyl xyloside,were collected with a total high purity.The aromatic derivatives were derived from the cleavage of the dominant intermolecular 4-O-5 and?-O-4 linkages between phenolic units in natural lignin.With the stepwise process,different weight molecular phenolics distributions were separated into three fractions by gradual reduction of the solvents.Due to their similar physical and chemical properties within each fraction,the platform chemicals can be designed into high added-value products.These platforms have great commercial potential for producing high-quality chemicals and biofuels using mild upgrading conditions.5.Phenolic compounds derived from biomass are important feedstocks for the sustainable production of hydrocarbon biofuels.Hydrodeoxygenation is an effective process to remove oxygen-containing functionalities in phenolic compounds.This paper reported a simple method for producing hydrocarbons by liquefying biomass and upgrading liquefied products.Three phenolic compounds fractions?1#,2#,and 3#?were separated from liquefied biomass with stepwise precipitation and extraction.Three phenolic compounds fractions were hydrogenated and deoxygenated to cyclohexanes using bifunctional catalysts via in situ hydrodeoxygenation.During the in situ hydrodeoxygenation,we introduced bifunctional catalysts combined of Raney Ni with HZSM-5.The bifunctional catalysts showed high selectivity for removing oxygen-containing groups in biomass-derived phenolic compounds.And the hydrogen was supplied by aqueous phase reforming of methanol without external H₂.Additionally,the mechanism based on our investigation of in situ hydrodeoxygenation of phenolic compounds was proposed.During the in situ hydrodeoxygenation,the metal-catalyzed hydrogenation and acid-catalyzed hydrolysis/dehydration were supposed to couple together.Current results demonstrated that in situ hydrodeoxygenation using bifunctional catalysts is a promising and efficient route for converting biomass-derived phenolic compounds into fuel additives and liquid hydrocarbon biofuels.