Guozhi Fan

Isolation of cellulose from rice straw and its conversion into cellulose acetate catalyzed by phosphotungstic acid.

Cellulose was isolated from rice straw by pretreatment with dilute alkaline and acid solutions successively, and it was further transferred into cellulose acetate in the presence of acetic anhydride and phosphotungstic acid (H3PW12O40·6H2O). The removal of hemicellulose and lignin was affected by the concentration of KOH and the immersion time in acetic acid solution, and 83wt.% content of cellulose in the treated rice straw was obtained after pretreatment with 4% KOH and immersion in acetic acid for 5h. Phosphotungstic acid was found to be an effective catalyst for the acetylation of the cellulose derived from rice straw. The degree of substitution (DS) values revealed a significant effect for the solubility of cellulose acetate, and the acetone-soluble cellulose acetate with DS values around 2.2 can be obtained by changing the amount of phosphotungstic acid and the time of acetylation. Both the structure of cellulose separated from rice straw and cellulose acetate were confirmed by FTIR and XRD.

Amberlyst 15 as a new and reusable catalyst for the conversion of cellulose into cellulose acetate

The acetylation of cellulose using sulfonated Amberlyst 15 as a new and reusable catalyst was investigated. Optimization of the acetylation process was carried out by variation in the amount of added catalyst, acetic acid, and acetic anhydride as well as the reaction conditions, which includes reaction time and reaction medium. Cellulose acetate, with a degree of substitution (DS) value of 2.38 and yield of 54.1%, was obtained under the optimized conditions and characterized using Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis-derivative thermogravimetry (TGA-DTG), and differential scanning calorimetry (DSC). The sulfonated polymer catalyst could be easily recovered by centrifugation after acetylation. Both the fresh and recovered catalysts were characterized by means of FTIR, TGA-DTG, DSC, and scanning electron microscopy (SEM), and the recovered catalyst could be successfully reused without further treatment. It was found that Amberlyst 15 possessed excellent catalytic stability, no significant changes in the DS values, and consistent yields of cellulose acetate observed over four reaction cycles.

ZnBr2 supported on silica-coated magnetic nanoparticles of Fe3O4 for conversion of CO2 to diphenyl carbonate

A magnetic Fe3O4@SiO2–ZnBr2 catalyst was prepared by supporting ZnBr2 on silica-coated magnetic nanoparticles of Fe3O4 and used as a recoverable catalyst for the direct synthesis of diphenyl carbonate (DPC) from CO2 and phenol in the presence of carbon tetrachloride. The as-prepared catalyst was characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), a X-ray photoelectron spectrometer (XPS) and BET. Zn loading in the supported catalyst and leaching during the reaction process were determined by atomic absorption spectroscopy (AAS). It was found that Fe3O4@SiO2–ZnBr2 showed higher catalytic activity than homogenous ZnCl2 and ZnI2 as well as homogenous ZnBr2. With this new catalyst under optimized conditions, a yield of DPC at 28.1% was obtained. The heterogeneous catalyst Fe3O4@SiO2–ZnBr2 can also be recovered by a permanent magnet after the reaction and reused up to 4 times without noticeable deactivation.

Lewis Acid-Promoted Suzuki Reaction using Palladium Chloride Anchored on a Polymer as a Catalyst

Palladium chloride anchored on polystyrene modified by 5-amino-1,10-phenanthroline was prepared and used as an efficient recoverable catalyst for Suzuki cross-coupling reactions. The heterogeneous catalysts can be easily separated from the reaction mixture and reused for five cycles without significant Pd leaching and loss of catalytic activity. Rate enhancement in the Suzuki reaction by Lewis acids was also studied.

Synthesis of Diphenyl Carbonate from Carbon Dioxide, Phenol, and Carbon Tetrachloride Catalysed by ZnCl2 Using Trifluoromethanesulfonic Acid as Functional Co-Catalyst

Diphenyl carbonate (DPC) was synthesised from carbon dioxide, phenol, and carbon tetrachloride catalysed by the Lewis acid ZnCl2 with the addition of co-catalyst. It was found that common bases are not effective co-catalysts for the production of DPC, and only slight enhancement in the catalytic activity of ZnCl2 was observed in the presence of inorganic additives such as inorganic carbonates and quaternary ammonium salts. Although poor conversion of phenol and yield of DPC were obtained using ZnCl2 or trifluoromethanesulfonic acid (CF3SO3H) as the sole catalyst, the catalytic activity of ZnCl2 was significantly improved by the addition of a catalytic amount of CF3SO3H. CF3SO3H has been proven to be an effective co-catalyst. The conversion of phenol and the yield of DPC were dependent on the amount of ZnCl2 and CF3SO3H, the reaction temperature, and the pressure of CO2. A possible reaction mechanism for the synthesis of DPC catalysed by the co-catalytic system including ZnCl2 and CF3SO3H was also proposed.

Synthesis of 5-hydroxymethyl furfural from cellulose via a two-step process in polar aprotic solvent

The synthesis of 5-hydroxymethyl furfural (HMF) from cellulose via a two-step process was investigated. To optimize reaction conditions, the separate conversion of cellulose and glucose was first performed in tetrahydrofuran (THF) and N, N-dimethylformamide (DMF) via a one-step process using hosphotungstic acid (PHA) as catalyst. The direct conversion of cellulose to HMF was then performed via the two-step process. The first step and the second step were carried out in THF and the mixture solvent composed of THF/DMF, respectively. Cellulose was converted to HMF and glucose in the first step in THF. Both of cellulose and the as-formed glucose were then converted to HMF in the second step. The conversion of cellulose to HMF and glucose were significantly improved by the two-step process, and the total yield of HMF and glucose was elevated from 52.1 to 97.0%. A possible mechanism for the formation of HMF from cellulose via the two-step process was also proposed.

Synthesis and Characterization of Magnetic TiO2 Hollow Nanofibers via Electrospinning Assisted Sol-Gel Process

The PVP/Fe3O4/TBT composite nanofibers have been successfully fabricated via a facile electrospinning assisted sol-gel process, and magnetic TiO2 hollow nanofibers are obtained by the calcination process. The effects of TBT and Fe3O4 dosage on the morphologies and hollow structure of nanofibers are systematically investigated. Scanning electron microscopy (SEM) demonstrated that the magnetic TiO2 nanofibers had a hollow structure with the average diameter of 200 nm. XRD results exhibited that magnetic TiO2 hollow nanofibers with well crystallized anatase phase were obtained. Both the hollow structure and well crystallized anatase phase of TiO2 nanofibers play very important role in photocatalytic activity. Moreover, the magnetic test demonstrated TiO2 hollow nanofibers possessed an excellent magnetic responsiveness, which facilitated the separation of TiO2 hollow nanofibers.