The esterification of malic acid using traditional homogenous catalysts suffers from the difficulty in reuse of the catalyst and undesirable side reactions. In this work, Zr(SO4)2/SiO2and Zr(SO4)2/activated carbon (AC) as solid acid catalysts were prepared for malic acid esterification with methanol. The conversion of malic acid over these two catalysts is comparable to that over H2SO4and unsupported Zr(SO4)2∙4H2O catalysts; however; a 99% selectivity of dimethyl malate can be realized on these two supported catalysts, which is much higher than that of conventional H2SO4(75%) and unsupported Zr(SO4)2∙4H2O (80%) catalysts, highlighting the critical role of AC and SiO2supports in tuning the selectivity. We suggest that the surface hydroxyls of AC or lattice O2−ions from SiO2donate electrons to Zr4+in Zr(SO4)2/AC and Zr(SO4)2/SiO2catalysts, which results in the increase in electron density on Zr4+. The enhanced electron density on Zr4+reduces the degree of H delocalization from crystal water and then decreases the Brønsted acid strength. Consequently, the reduced Brønsted acid strength of Zr(SO4)2/AC and Zr(SO4)2/SiO2catalysts suppresses the intermolecular dehydration side reaction. In addition, these two supported catalysts can be easily separated from the reaction system by simple filtration with almost no loss of activity.Keywords:malic acid;catalytic esterification;solid acid catalyst;Zr(SO4)2;intermolecular dehydration
WANG DING-KAI,ZHAO WEI,CUI MING-YU,GUO TIAN-TIAN,FU SHUI-YUAN,LI WEI-GANG
A series of Zr(SO4)2/SiO2 solid acid catalysts with different Zr(SO4)2 loadings were prepared by water-soluble-impregnation method at room temperature. Then, the prepared catalysts were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and energy-dispersive X-ray spectrum, X-ray diffraction, adsorption/desorption of N2, and temperature-programmed desorption of NH3. The results showed that the active component Zr(SO4)2 was successfully adhered to the mesoporous SiO2, and the acid amount of Zr(SO4)2/SiO2 increased with the increasing of the Zr(SO4)2 loadings. Finally, the wheat stalk was used as raw material and depolymerized over Zr(SO4)2/SiO2 to produce ethyl levulinate (EL). The reaction mixture was separated and purified by filtration and vacuum distillation. The kinetic characteristics and the reaction pathway were also studied. A comparative study showed that 20 wt.% Zr(SO4)2/SiO2 exhibited higher catalytic activity. When reaction temperature, time, catalyst dosage and Zr(SO4)2 loadings were 190 °C, 50 min, 20 wt.% and 30 wt.%, the EL yield reached a maximum of 17.14%. The relative content of EL exceeded 90% after three steps of distillation.
Down fibers is the most popular filling material and widely applied in daily life products such as homes, apparel and sporting gear due to its features of being natural, soft and warm keeping. The fluffiness is quite important to reflect the excellent performance of down fibers. However, owing to the short feeding cycle of poultry, the high content of immature down fibers leads to low fluffiness, which affects the quality of down fibers. In our work, the down fibers with amount of maximum raw materials and the fluffiness of 450 cm 3 /30 g were taken as the research samples. Clean and efficient alkaline zirconium sulfate was used as fluffing agent of down fibers. The cost of using alkalized zirconium sulfate treatment is relatively cheap compared with the traditional fluffing agent glutaraldehyde. Different doses of alkalized zirconium sulfate were used to cross-link the natural down fibers to improve the fluffiness. The results showed that when the dosage of alkalized zirconium sulfate was 2% of the weight of fibers, the performance of down fibers were the best and the fluffiness increased by 25%. It has a good practical significance to improve the economic benefits of down manufacturers. Meanwhile, the down fibers treated with alkalized zirconium sulfate were characterized by Energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Differential scanning calorimetry (DSC) and the changes of free amino content. Furthermore, measurement of zirconium ion concentration in wastewater by ICP showed that alkaline zirconium sulfate has achieved high absorption efficiency. Moreover, ultra depth microscope observation showed that the down fibers treated with alkalized zirconium sulfate have a better dyeing performance compared to untreated fibers. Overall, this work contributed a new insight into the sustainable development of down industry, and it further confirmed that it is a good approach to use the alkalized zirconium sulfate as the fluffing agent to improve the performance of down fibers.
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