Conversion Of Biomass-derived Furfuryl Alcohol To Ethyl Levulinate

Ethyl levulinate（EL）is an important platform compound that promotes the clean burning of diesel and reduces harmful emissions.Compared to traditional fossil feedstocks,biomass feedstocks are widely available,inexpensive,renewable,green and non-polluting.Furfuryl alcohol（FA）is an essential intermediate derived from biomass degradation,and acid-catalyzed conversion of FA to EL in ethanol is now a common method for synthesizing EL.The preparation of recyclable,non-polluting,low-cost,high-performance acid catalysts and the optimization of catalytic conditions are essential to improve the conversion of FA to EL.Consequently,this thesis focuses on the synthesis of acid catalysts and their catalytic properties,with the following main research and conclusions:（1）A porous carbon-based sulfonic acid solid-acid catalyst,YS-SO₃H,was synthesized using calcined waste yeast cells as a carrier and H₂SO₄as a sulfonating agent.YS-SO₃H was used in the reaction of FA alcoholysis for the preparation of EL.Optimization of the catalytic conditions showed that the FA conversion and EL yield reached 98.21%and 94.73%,respectively,for a 2 h reaction at 120°C under YS-SO₃H.YS-SO₃H was recovered by centrifugation and reused three times,and the FA conversion and EL yield still reached 80.82%and 72.51%.The YS-SO₃H was regenerated after 3 reuses.The FA conversion and EL yields were restored to 97.33%and 90.42%,respectively.On the basis of FT-IR,XRD,TG,BET and XPS characterization results show that the carrier carbon based material was irregular in shape and the pore size was not homogeneous.The reason for the high catalytic activity and stability of YS-SO₃H is that the sulphonic acid group is connected to the irregular carbon base material through a chemical bond,and the introduction of the sulphonic acid group increases the acid active sites in the catalyst that are beneficial for the reaction to proceed.（2）In order to avoid the influence of the shape of the carrier material,polystyrene microsphere sulfonic acid（PS-SO₃H）with uniform size was synthesized.The porous carbon-based sulfonic acid solid-acid catalyst PS-SO₃H was synthesized using polyethylene microspheres of uniform pore size synthesized by the solvation method as the carrier and H₂SO₄as the sulfonating agent.The optimum catalytic conditions were 1.5 h reaction at 120°C under PS-SO₃H.FA conversion and EL yield reached 99.52%and 94.71%,respectively.PS-SO₃H was recovered by centrifugation and reused three times,and the FA conversion and EL yield could still reach 90.82%and 82.54%.The catalytic activity of PS-SO₃H was measured again by regeneration after 3 times of reuse.The FA conversion and EL yield returned to 96.32%and90.41%.The characterization results showed that the polyethylene microsphere carriers in PS-SO₃H were homogeneous in size and shape,and successfully sequestered the sulphonic acid.Activation energies for the reactions catalyzed by YS-SO₃H and PS-SO₃H were 17.45 k J/mol and 23.83 k J/mol respectively,indicating that the catalytic activity of YS-SO₃H was significantly higher than that of PS-SO₃H,which was caused by the higher total acidity of YS-SO₃H compared to PS-SO₃H.（3）During the synthesis of catalysts using waste yeast cells and polyethylene microspheres as carriers,Br（?）nsted acid could not be completely sequestered,resulting in its low utilisation.In order to improve the Br（?）nsted acid utilisation,the ionic liquid catalyst[PSna][HSO₄]was synthesized with niacin and 1,3-propanesulfonic lactone.The best optimal catalytic conditions were 2 h reaction at 110°C under[PSna][HSO₄],with FA conversion and EL yield of 97.79%and 96.10%,respectively.The extraction and recovery of[PSna][HSO₄]was repeated 5 times,and the FA conversion and EL yield could still reach 93.74%and 88.17%.The characterization results show that the amphoteric compound formed by the reaction of imidazole with 1,3-propanesulfonic lactone can be fully coupled with sulfuric acid to form ionic liquid[PSna][HSO₄].The activation energy of the reaction catalyzed by[PSna][HSO₄]was 12.23k J/mol.Density flooding theory（DFT）calculations were employed to determine the most probable reaction pathways,identify all possible transition states and the reaction energy barriers overcome at each step of the reaction.（4）A solid-loaded functionalized ionic liquid catalyst[PS-CH₂OCH₂N（CH₃）₃][HSO₄]was synthesized to solve the problem of difficult recovery of homogeneous ionic liquid catalysts.The optimum catalytic conditions were as follows:the reaction was carried out at 120°C for 2h.The FA conversion and EL yield reached 98.51%and 92.42%,respectively,Under the catalysis of[PS-CH₂OCH₂N（CH₃）₃][HSO₄].Centrifugal recovery of[PS-CH₂OCH₂N（CH₃）₃][HSO₄]was repeated three times,and the FA conversion and EL yield still reached 85.42%and 74.87%.The reused[PS-CH₂OCH₂N（CH₃）₃][HSO₄]was regenerated immersion and reused again,and the FA conversion and EL yield were restored to 96.39%and90.13%.It was characterized that the microsphere surface was successfully grafted with quaternary ammonium salt,which was then coupled with sulphuric acid to form a stable solid-loaded ionic liquid[PS-CH₂OCH₂N（CH₃）₃][HSO₄].The activation energy of the reaction catalyzed by[PS-CH₂OCH₂N（CH₃）₃][HSO₄]is 33.56 k J/mol.（5）In order to solve the problem of environmental damage at the Br（?）nsted acid catalytic site in the above catalysts,a solvothermal method was employed to prepare Lewis acidic metal-organic complexes of zirconium imidazolium propane sulfonate Zr-HIMPs.The optimum catalytic conditions were 2 h reaction at 120°C under the catalysis of Zr-HIMPs.The results were 95.03%FA conversion and 92.02%EL yield,respectively.The Zr-HIMPs were recovered by centrifugation and reused five times,and the FA conversion and EL yield could still reach86.55%and 80.64%.Results showed that the Zr-HIMPs had an irregular shape and were structurally stable,and the activation energy of the reaction catalyzed by Zr-HIMPs was 35.61k J/mol.By increasing the amount of Zr-HIMPs,the catalytic effect was similar to that of the previous Br（?）nsted acid catalysts.（6）On the basis of the above studies,the reaction solvent was further modified.A small molecule catalyst 5-SSA was added to catalyse FA to EL.At the same time,the hydrogen bond acceptor choline chloride（Ch Cl）was added to the reaction system to form deep-eutectic solvent（DES）coupled with ethanol.The results of the catalytic reaction were 94.91%FA conversion and 88.82%EL yield at 100°C for 2 h.Density flooding theory（DFT）calculations were utilized to investigate all possible reaction pathways for the alcoholysis of FA to EL in acidic DES.It was shown that the coupling of Cl in Ch Cl with H in-OH in ethanol enables a rapid conversion to the ethoxy group of the transition structure,increasing the rate of ethoxy generation and accelerating the FA alcoholysis reaction.In the 5-SSA catalytic system,the addition of Ch Cl was able to reduce the activation energy of the reaction by 16%,effectively increasing the rate of the FA alcoholysis reaction to EL.