Synthesis Of Novel Solid Acid Catalysts And Its Application For The Acetalization Of Glycerol With Acetone

Biodiesel is an advanced biofuel with renewability,cleanliness and excellent combustion performance,which is thought to be an effective supplement to traditional fossil diesel.The application of biodiesel can effectively reduce the dependence on fossil fuels,increase employment,and improve environmental quality.Due to the rapid development of the biodiesel industry,the amount of by-product glycerol is also rapidly increasing,and the conversion of glycerol into high value-added products has become a research hotspot.Among the reported literatures,the acetalization of glycerol is a new direction which has recently attracted people's attention.The acetalization of glycerol with acetone is a typical acid-catalyzed reaction,mainly producing two isomers,2,2-dimethyl-1,3-dioxo-penta-4-methanol and 2,2-dimethyl-1,3-dioxol-5-ol,wherein the major product is the five-membered ring product commonly named as solketal.The reaction is a reversible exothermic reaction with a by-product of condensation water,so the presence of water would suppress the progress of the reaction.Therefore,finding a heterogeneous acid catalyst with suitable acidity and water resistance is the main goal of this research direction.In this work,varieties of solid acid catalysts were prepared.The catalysts'activities were evaluated in the acetalization of glycerol with acetone in detail and the reaction process was optimized.Various characterizations were employed to investigate the composition,structure,morphology and surface properties of catalysts.The relationship between the structure and the properties of the catalyst was analyzed and the reaction mechanism over the catalyst was proposed.The main results are as follows:A series of solid acid catalysts with different ratio of Co/Al were prepared via a controlled calcination of Co-Al layered double hydroxide precursor,and they were evaluated in the acetalization of glycerol with acetone.Experimental results showed that the activity of Co[?](Co[?]1.25Al0.75)O4 was the highest.Under the optimized conditions(130 ?,acetone/glycerol= 10:1,5 wt%catalyst,3 h),the conversion of glycerol reached 69.2%,and the selectivity of 5-membered ring product solketal was as high as 98.6%.Characterization results showed that the Co/Al ratio of the catalyst affected the the composition,crystal structure,morphology,specific surface area and surface acid density of the catalyst.The activity of catalyst is strongly related to the amount of strong acid on its surface,and the conclusion that acetalization of glycerol with acetone mainly proceeded over the strong acid site of the catalyst was first presented and demonstrated.A series of a-zirconium phosphate catalyst with different crystalline phases were prepared via controlling calcination of ?-zirconium phosphate precursor with layered structure,and the activities and stabilities of the catalysts in the acetalization of glycerol with acetone were detected.Research fingdings showed that the strong acid sites of Zr(HPO4)2 were mainly derived from the P(OH)group on the surface of layered Zr(HPO4)2 structure.When the calcination temperature was below 300 0C,the layered structure was very stable,so its total acid amount and surface acid density were very high.The obtained activity in the acetalization of glycerol with acetone is high with great stability.Under optimal conditions(50 ?,acetone/glycerol=10:1 and 5 wt%catalyst),the conversion of glycerol was up to 85.7%with a 5-membered ring product solketal selectivity of 98.6%over ZrP-200,and the TOF value was up to 47.7 h-1,which showed a good application prospect.In order to overcome the inhibition of condesation water on reaction and acid center of catalyst,which was produced in the acetalization of glycerol,a series of zirconium phenylphosphonate catalysts with flower-like morphology were designed and prepared from different substrates and applied in the acetalization of glycerol with acetone.The composition,structure,morphology and hydrophilic or hydrophobic properties of the catalysts were characterized in detail.Experiment results showed that when part of hydroxyl groups of zirconium phosphate were replaced by phenyl groups,the acid amount of catalysts was decreased,but the hydrophobicity and the acid density were increased.Considering the dual character caused by the introduction of the phenyl groups,ZrPP-20 had moderate acid strength and hydrophobicity,and thus had the best activity with excellent stability in the acetalization of glycerol with acetone.The conversion of glycerol reached 90.2%in 6 h at 40 ? with an acetone/glycerol ratio of 10 and 5 wt%catalyst.In addition,ZrPP-20 was also applied in the acetalization of glycerol with a series of aldehydes and ketones,and excellent activities were also detected.In order to overcome the instability of sulfonatd phenolic resin in aqueous solution,a series of silica dioxide supported sulfonated phenolic resin catalysts were successfilly prepared by impregnation,in situ TEOS hydrolysis and modified-TEOS hydrolysis methods.Characterization results showed that the use of KH560 coupling agent and the synthesis conditions enhanced the interaction between silica dioxide and sulfonated phenolic resin.The polymer can be effectively dispersed on the surface of support,and the abundant sulfonic acid groups can be retained and fixed,which improved the activity and stability of catalyst.It was found that the SPF-K-Si-2 prepared by modified-TEOS hydrolysis method was highly active.At 40 ? and with acetone/glycerol ratio of 10 and 5 wt%catalyst,the conversion of glycerol in the reaction could reach 92.8%in 1 h over SPF-K-Si-2,and there was no significant decrease in activity after 5 cycles,indicating that the stability of the catalyst is remarkably improved.