Study On The Catalysts And Process Parameters For The Acid-catalyzed Acetalization Of Acetone With Glycerol

The biodiesel as a renewable fuel has been appealled to more and more attention,As well known, in the common production biodiesel via transesterification of vegetableoil or animal fat with methanol or ethanol, about1kg of crude glycerol as by-productwill be formed for every9kg of biodiesel. With the rapid increase on glycerolproduction due to the use of biodiesel worldwide, it will interrupt the original balance ofglycerin market. Therefore, it is very important to effectively utilize glycerol for thedevelopment of this industry. Because all three hydroxyl groups are located in theadjacent carbon atoms of glycerol, it can be dehydrated to acrolein, the glycerol can beconverted by hydrogen to glycol1,2-and1,3-propanediol, synthesized toN-heretocyclic compounds, reformed by steam to hydrogen and synthesis gas, etc.The recent studies indicate that glycerol can transform to acetal compoundsthrough acetalization with aldehydes （ketones）. With special aroma, acetal compoundsare widely used in tobacco, cosmetics, etc, but also used in metal processing, industrialcleaning, oil, pesticides and other industries as a surfactant. It has been discovered thatthe acetalization of glycerol with acetone can also be carried out to produce two mainproducts:（2,2-Dimethyl-1,3-dioxolane-4-yl）-methanol （Solketal） and2,2-dimethyl-1,3-dioxan-5-ol （5-ol）. The former is an important organic compound which can act assolvent, plasticizer, surfactants, flavours, pharmaceutical intermediate, rapid hemostat,histo-agglutinant. In recent years, it has been found that Solketal derivatives has thepotential to be used as gasoline additive, especially suitable for catalytic crackinggasoline.The present work focuses on the preparation of SiO₂-TiO₂and ZrO₂-SiO₂catalysts with different SiO₂/TiO₂, ZrO₂/SiO₂molar ratio, calcination temperature and the effectsof acetalization parameters such as reaction temperature, acetone/glycerol, catalystamount and reaction time on the glycerol acetalization with acetone are furtherinvestigated in detail. And at the same time, the corresponding catalysts are alsocharacterized by using XRD, NH₃-TPD, FT-IR, UV-vis, N2adsorption-desorption andso on. Based on the mentioned-above researchs, the reaction mechanism for theacetalization of glycerol with acetone are discussed. The obtained original results arelisted as follows:（1） Glycerol acetalization with acetone on catalysts are found to give two mainproducts:（2,2-Dimethyl-1,3-dioxolane-4-yl）-methanol （Solketal） and2,2-dimethyl-1,3-dioxan-5-ol （5-ol）;（2） The characterization results of catalysts with a different SiO₂/TiO₂molar ratioby using XRD, UV-Vis, FT-IR exhibit that SiO₂-TiO₂samples mainly exhibitamorphous, and Ti species should be highly dispersed in these materials. The results ofUV-vis-DRS show that the obtained ySiO₂-TiO₂samples in the present work mainlyconsist of Ti-O-Si groups and small amount of low polymeric amorphous TiOxspeciesdispersed by amorphous SiO₂;（3） The simultaneous presence of TiO₂and SiO₂in SiO₂-TiO₂samples will lead tothe formation of Si-O-Ti linkages, which probably adsorb more water molecular.Br nsted acidic sites of SiO₂-TiO₂are supported by O-H groups from the adsorbedwater molecules on Si-O-Ti or Si-O-Si linkage;（4） The optimum preparation conditions of SiO₂-TiO₂: SiO₂/TiO₂molar ratio of1,calcination at550oC in air;（5） A low calcination temperature for SiO₂-TiO₂is perhaps difficult to form thestable Si-O-Ti linkages, however the high temperature can give rise to the breakage ofSi-O-Ti linkages, which is perhaps disadvantageous to the formation of acidic sites;（6） The catalytic performance of SiO₂-TiO₂to glycerol-acetone acetalizationreaction is better than the1.0Al2O3-TiO₂, it due to catalyst surface acidity andwater-tolerant performance. The former possesses better water resistance property thanthe latter, which will be good for the reaction progress;（7） The optimum preparation conditions of ZrO₂-SiO₂: ZrO₂/SiO₂molar ratio incatalyst was0.5and the ideal catalyst calcination temperature was500oC;（8） The NH₃-TPD characterization results of ZrO₂-SiO₂show that the total acidicdensity and acidity of catalyst with ZrO₂/SiO₂molar ratio of0.5exhibits the biggestvalue. Too higher or lower ZrO₂/SiO₂molar ratio can make them decline; （9） According to FT-IR results, Si-O-Zr linkages have been found to be formed inZrO₂-SiO₂prepared by sol-gel method;（10） For the SAPO catalysts, the doping of V is helpful to formation of SAPO-5molecular sieve from silicon aluminium phosphorus compounds;（11） The surface acidic characteristic of SAPO catalysts can be related to catalystcomposition and roasting temperature;（12） The optimum conditions of glycerol acetalization with acetone are:acetone/glycerol molar ratio=1，catalyst amount2.2g per10g of glycerol, reactiontemperature being70oC;（13） Glycerol acetalization with acetone mainly carries out on Br nsted acidic sitesby the water-adsorbed Si-O-Ti linkages. The formation of solketal with5-memberedring as the main product of glycerol acetalization with acetone is mainly governed bykinetics and another ketal with a6-membered ring is controlled by thermodynamics.