Study On Synergistic Conversion Of Lignin Oxidation Products To Adipic Acid

Lignin is an alkyl aromatic polymer that exists in plant cell walls and it is used for defense,composition and water transport.Due to the diversity of lignocellulose,lignin is an underutilized resource in the production of lignocellulose biomass fuels and chemicals,but its value is crucial to the development and success of the biofuel industry.Despite its high energy content,lignin can only be used as fuel in modern biorefinery because of its inherent heterogeneity and stubbornness,while cellulose and hemicellulose are converted into renewable fuels and chemicals.In nature,lignin depolymerization is mainly accomplished by decaying fungi and oxidase from some bacteria.Aromatic monomers are released during cell wall depolymerization in plants,and many methods have been developed to metabolize these aromatic substances.Muconic acid is a promising commercial chemical intermediate.It can be converted into numerous downstream products,including adipic acid,which is the most important dicarboxylic acid in commerce.The market demand for adipic acid is 2.6 million tons per year,and the annual demand is expected to increase by 3-3.5%.Adipic acid can be used as a polymer precursor of nylon,plasticizer,lubricant and polyester polyols.Conventional adipic acid production involving nitric acid oxidation of benzene is highly destructive to the environment.However,recent studies have shown that it is more economical and environmentally friendly to synthesize adipic acid from lignin by using biological and chemical catalytic methods.Therefore,we use metabolic engineering and genetic engineering to convert lignin oxidation products into muconic acid through catalysis and separation,and to prepare adipic acid by subsequent catalytic hydrogenation.Firstly,Pseudomonas putida KT2440 produces mucoconic acid through genetic engineering and metabolic engineering fermentation to achieve biochemical transformation of atomic efficiently.Because the engineering strain is suitable for genetic manipulation,it can withstand various physical and chemical pressures,and utilize many aromatic molecules derived from lignin.The metabolic ability of Pseudomonas putida KT2440 modified by metabolic engineering was evaluated in shaking flask experiment.It was proved that lignin oxidized products could be used as carbon source of fermentation substrate of Pseudomonas putida.Pd/C is recognized as a highly active catalyst for the catalytic hydrogenation of muconic acid to adipic acid.Screening of Pd/C with different particle sizes made in laboratory and commercialized Pd/C catalysts,it is feasible to convert adipic acid efficiently at low temperature and low pressure.By esterification with ethanol and ethylene and Diels-Alder reaction,the solubility of muconic acid was increased,and cycloaddition compound was formed.Further dehydrogenation reaction resulted in diethyl terephthalate(DET).The product was analyzed and characterized by GC-MS.