Catalytic Conversion Of Cellulose To Lactic Acid

Cellulose has attracted extensive attention as an important biomass resource because of its widespread distribution in nature and benign benefits of ecology and economy as well as society. It holds enormous potential as an excellent replacement for fossil resource. Lactic acid has been identified as a versatile green platform compound, which has been widely applied in pharmaceuticals, food, cosmetic and biodegradable plastics. It is also considered to be a promising and numerous potential fine chemical.This thesis mainly use cellulose as a feedstock to synthesize lactic acid in different catalytic systems, the main contents are as follows:(1) The hydrothermal conversion of cellulose to lactic acid catalyzed by Lanthanide triflates as a new type of Lewis acid catalysts were studied, and the relationship between catalytic activities and cation ionic radius were investigated. Additionally, influences of various parameters including reaction temperature, time, cellulose amount, catalyst dosage on the catalytic performance were investigated. The results show that the yield of lactic acid increase with decreasing cation ionic radius, and Er(OTf)3 exhibits the best catalytic performance because of its the smallest ionic radius. A cooperative effect exists between the hydroxonium ion from water autoprotolysis and the homogeneous Lewis acid catalyst. The former could be the driving force responsible for the cellulose depolymerisation into soluble intermediates, and the latter would accelerate the transformation of the intermediates into final and stable products, e.g. lactic acid, formic acid, levulinic acid, acetol etc. Lactic acid yields as high as 89.6% were obtained when reacting 0.1 g cellulose,0.05 g catalyst and 30 mL water at 240℃ under 2 MPa N2 for 30 min using Er(OTf)3 as the catalyst.Moreover, this catalyst could be reused at least five times without obvious loss of activity.(2) Various erbium ion-exchanged montmorillonite K10 materials were prepared by an ion exchange method and were found to act as efficient solid acid catalysts. The catalytic materials synthesized in this work were characterized using a combination of X-ray fluorescence spectroscopy, N2 physical adsorption, powder X-ray diffraction, Fourier transform infrared spectroscopy, inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy and NH3 temperature-programmed desorption, as well as by analysis of FT-IR spectra following pyridine adsorption. These catalysts were also evaluated with regard to the hydrothermal conversion of cellulose to lactic acid. It was found that the montmorillonite does not have a significant influence on the catalytic activity as such, but rather serves primarily as a support to anchor the active erbium ions. Lactic acid yields as high as 67.6% were obtained when reacting 0.3 g cellulose,0.1 g catalyst and 30 mL water at 240℃ under 2 MPa N2 for 30 min. Upon recycling of the catalyst, the lactic acid yields decreased from 67.6 to 58.7 to 55.9% during the first, second and third trials. Beginning with the second trial the catalyst behaved as a true heterogeneous catalyst for the conversion of cellulose to lactic acid. The observed decreases in catalytic activity during recycling could be due to a combination of erbium ion leaching, deposition of carbon species in pores and partial structural changes in the catalyst.(3) Various erbium ion-exchangedp and H-ZSM5 zeolites were prepared. These catalysts were evaluated for the catalytic conversion of cellulose to lactic acid. Several techniques including XRF, ICP-OES, BET, XRD, XPS, NH3-TPD and FT-IR of pyridine adsorption were used for the characterization of the modified catalysts. The results show that under the conditions of 0.3 g cellulose,0.1 g catalyst,30 mL water, 240℃,2 MPa N2 for 30 min lactic acid yields of 57.9% were obtained using an erbium ion-exchangedβ zeolite with 12.4 wt% of Er content. After being used 3 times, it still maintained ～50% lactic acids. While over erbium ion-exchanged H-ZSM5 zeolite with 8.6 wt% of Er content, lactic acid yields of 52.3% were obtained. This catalyst could be reused for three times with a slight decrease in activity.