Study On Catalysts For Dehydration Of Lactic Acid

Acrylic acid is an important unsaturation organic acid.Traditional industrial methods are all based on oil resources,which made the production of acrylic acid deeply depended on the oil resources.Due to the development of fermentation lactic acid,more attention was paid to the research of lactic acid dehydration to acrylic acid.However,the catalysts reported have a lot of problems such as the low selectivity of main product. In this thesis,several novel catalysts were synthesized,and their catalytic properties were tested in the dehydration of lactic acid.The structure and surface properties of these catalysts were characterized by using modern physical and chemical techniques,such as X-ray diffraction(XRD),Fourier transformation infra-red spectra(FT-IR),Nitrogen adsorption-desorption isotherms and Scanning electron micrograph(SEM),and so on.Various materials including HZSM-5,synthesized SiO₂,commercial SiO₂,activated carbon,TiO₂,MgO,bentonite were choosen as the support for sodium phosphate(Na₃PO₄).The catalytic performance of lactic acid dehydration in liquid-solid phase showed that the synthesized SiO₂ was the optimal support.The experimental results showed that under the loading amount of 1.0 mmol/g,impregnation at 50℃for 3 h,calcination at 300℃for 3 h can get the optimal catalyst.The FT-IR results showed that the same spectra between the two SiO₂ supports and the standard spectra,XRD results showed that the two supports have the same non-crystal bread curve,but the BET results showed larger surface area and pore size for the synthesized SiO₂.Layered hectorite-type solids were synthesized hydrothermally in the presence of surfactants in reaction medium.The structure of synthesized samples were investigated by FT-IR,XRD,SEM,TG-DTA,and BET. After modified by cerium,the catalysts obtained were applied for the reaction in gas-solid phase.The conversion of lactic acid was 33.5%over catalyst synthesized with no surfactant,while the selectivity of acetaldehyde and acrylic acid were 40.2%and 1.8%respectively.The conversion of lactic acid could be improved by the addition of surfactants in the process of catalysts synthesized,the selectivity of acrylic acid and acetaldehyde were changed.For modified hectorite catalysts the selectivity of by-products could be controlled around 45%,which make a big advancement from solid catalysts synthesized by SiO₂. To avoid the lack of natural hectorite,bentonite was choosen to instead of hectorite.The catalysts based on bentonite were activated by different concentration phosphoric acid,and then modified by cerium.The catalytic performances of the samples obtained above were tested in the dehydration of lactic acid in gas-solid phase.For crude bentonite as catalyst the conversion of lactic acid dehydration was 15.3%,the selectivity of acetaldehyde and acrylic acid were 61.4%and 2.5% respectively.After activated by 30%phosphoric acid for 8 h and modified by cerium,the conversion was 80.8%while the selectivity of acetaldehyde and acrylic acid were 51.8%and 6.9%.The experimental results showed that the conversion of lactic acid dehydration was higher than hectorite catalysts system,and the selectivity of by-products can be controlled around 32%.