Visible Light Catalysts Are Used In The Study Of Lignin Depolymerization

With the gradual depletion of natural resources,people pay more and more attention to renewable resources.Generally,renewable resources refer to those that can be repeatedly formed in a certain period after being used,consumed,processed,burned,discarded,etc.It's a type of natural or unnatural resource with self-renewing,self-recovering characteristics and sustainable use.Corresponding to non-renewable resources,it is necessary to strengthen the construction and promotion of green resources in sustainable development.Biomass energy is the form of energy stored in the form of chemical energy in biomass.It has always been one of the important energy sources for human survival.It is the fourth largest energy source after coal,oil and natural gas.The system occupies an important position.Lignin is a biopolymer with three-dimensional network structure formed by the interconnection of three phenyl-propane units through ether bonds and carbon-carbon bonds.It exists in woody tissues.In woody plants,lignin accounts for about 25%.It is the world's second most abundant organic.However,the complex and stable chemical bonds of lignin make the lignin depolymerization a difficult problem.The conventional methods for catalytically depolymerizing lignin generally require high temperature or high pressure conditions,but some of the free phenols and ?-alcohol functional groups cannot withstand such harsh reaction conditions.In order to solve this problem,we have tried to develope a method of depolymerizing lignin at room temperature under visible light to achieve the goal of sustainable development.This paper combines the concept of energy saving,environmental protection and sustainable development advocated by green chemistry,and applies visible light to the depolymerization lignin reaction.By constructing a novel homogeneous catalyst,the high-efficiency depolymerization of lignin model compound under normal temperature and normal pressure under visible light was achieved.In addition,in order to improve the utilization of light and explore the industrial application prospects of photocatalytic depolymerization lignin,this paper also explored the photocatalytic depolymerization of lignin in the micro-reactor,modulating different conditions and trying to deploymerize the natural lignin.The work described in this paper is mainly divided into the following two parts:1.In order to effectively alleviate the dependence on the transition metal catalyst when depolymerizing natural lignin,a non-metallic organic small molecule perylene catalyst(PDI)was successfully applied to the reaction of depolymerizing lignin model compounds under visible light conditions.More than 95% conversion and yield were obtained.For several common lignin monomer derivatives,the perylene catalyst PDI also showed good depolymerization activity,and the yield could reach more than 90%.In addition to the activity test in this paper,the reaction mechanism was explored by means of isotope-labeled and free radical trapping method,etc.It was concluded that the formic acid and lignin mimics formed an intermediate by hydrogen bonding,and then the photocatalyst produced electrons under photoexcitation,participated in the broken key process.2.In order to fully improve the utilization of light,we combine the depolymerization of lignin with the micro-reactor.It is inferred that the micro-reactor has better effect than the batch reactor in depolymerizing lignin mimics,and the conversion rate in the micro-reactor reaction can reach 99% at 54 minutes,and the conversion rate in batch reactor is only about 20%.In addition,the effects of factors such as the pressure of the micro-reactor,the flow rate,the amount of catalyst in the reactor,the amount of DIPEA/HCOOH added on the depolymerized of lignin,and the attempt of the micro-reactor were also explored successfully.Experimental investigation of the depolymerization of natural lignin,the fraction insoluble in ethyl acetate after the reaction is as low as 3.8%,which provides favorable support for the industrial depolymerization of natural lignin.