Green Synthesis Of Bio-based 1,4-butanediol Via Esterification And Hydrogenation Of Succinic Acid

1,4-Butanediol（BDO）is an important chemical product.Industrial large-scale synthesis of GBL and THF are using BDO as raw material.The dehydrogenation of BDO can be used to prepare GBL,and BDO dehydrates under acidic conditions to obtain THF.In addition,BDO is a synthetic monomer of biodegradable plastics PBAT（polyadipate/butylene terephthalate）and PBS（polybutylene succinate）.In recent years,due to the promulgations of the"plastic ban"and other policies,the market demand of biodegradable plastics PBAT and PBS is constantly expanding,which drives the market of their synthetic monomer BDO,with the annual demand exceeding 1 million tons!The BDO market is expected to reach$12.6 billion by 2025.However,at present,the production of BDO still relies on the traditional Reppe method,which accounts for 40%of the global market size of BDO.Reppe method uses non-renewable resources such as oil and natural gas as raw materials,which causes serious environmental pollution.In addition,there have been studies of direct hydrogenation of biomass succinic acid（SA）to produce BDO.SA is recognized by the US Department of Energy as one of the 12most promising biomass platform molecules.However,due to the difficulty of acid hydrogenation.Based on this,we proposed the route of esterification and hydrogenation of SA,through the selection of esterification and hydrogenation catalysts and changing the reaction conditions,the high yield of BDO synthesis from SA was realized.The details are as follows:1.For the esterification and hydrogenation of SA to synthesize BDO,the first step is to esterify SA and methanol to produce DMS,and the DMS yield of 100%is obtained under the catalysis of solid acid phosphotungstic acid.The second step is the hydrogenation of DMS to BDO.The optimal catalyst Cu₁Fe₁Al_0.5 can obtain 91.2%BDO yield,which is the highest reported so far.It was found that the excellent catalytic performance of Cu₁Fe₁Al_0.5 was attributed to the highly dispersed Cu nanoparticles and the weak total acid content on the surface,which inhibited the formation of byproduct esters and furans,while the segmented temperature control method also makes the product stay more in BDO because it considers the characteristics of the reaction at each stage.At the same time,the catalyst invented by us has strong stability.For the catalyst of esterification stage,it can be circulated five times in the batch reactor,the catalyst of hydrogenation stage can also be circulated five times in the batch reactor and displayed excellent long-term stability without deactivation in activity or BDO selectivity during 500 h of a time-on-stream test in a fixed-bed reactor.Detailed characterization analysis and intrinsic catalytic studies show that there is an interaction between Cu and Fe,which makes catalyst has high stability and broad industrial application prospects.This work provides guidance for the green industrial production of 1,4-butanediol.At the same time,it also provides a reference for improving the selectivity of one main product in complex continuous hydrogenation reactions which are controlled by many factors.2.We prepared a series of Cu Mn Al catalysts by coprecipitation method and tested their catalytic performance in the hydrogenation of DMM to BDO.By comparing the hydrogenation performance of Cu Mn Al catalysts with different proportions at constant temperature,the optimal Cu/Mn/Al molar ratio was selected as 1:1:1.On this basis,in order to further improve the selectivity of BDO,we optimized the reaction conditions.Considering the complexity of DMM hydrogenation reaction,the optimal reaction conditions of each stage reaction are not the same,we still use the segmented temperature control method in the first part of the work to adapt to the characteristics of each stage of the hydrogenation process as far as possible.Through the screening of reaction conditions,it was found that the optimal proportion of Cu₁Mn₁Al₁ catalyst reacts at 240℃for 4 h,and then continues to react at 170℃for 12 h,the yield of BDO can reach 90.1%.It is found that the reaction temperature and time of the Cuu Mn Al catalytic system at GBL-BDO stage are lower than that of the Cu Fe Al system,which reduces the energy consumption of the reaction process to a certain extent.