Catalytic mechanism and reaction pathway of acetone ammoximation to acetone oxime over TS-1

Weihong Xing,Zhaohui Li,Rizhi Chen,Wanqin Jin 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.5

A series of two-step reactions and several special experiments were designed and carried out to discover the reaction pathway of acetone ammoximation to acetone oxime over titanium silicalites-1 (TS-1) employing 25 wt%ammonia and 30 wt% hydrogen peroxide as the ammoximation agents. The experimental results show that the acetone oxime can form even if there is no direct contact between acetone and TS-1 catalysts, indicating the hydroxylamine route may be the most important catalytic mechanism for the reaction. HPLC, GC/MS and ion chromatography characterization results show that hydrogen peroxide can oxidize acetone oxime to acetone, nitrite and nitrate in the presence of TS-1. In addition, nitrite and nitrate can form in the reaction of H2O2 and NH3 over TS-1. Based on these results,a possible overall reaction pathway of acetone ammoximation over TS-1 has been proposed.

Effect of initial solution apparent pH on the performance of submerged hybrid system for the p-nitrophenol hydrogenation

Rizhi Chen,Yan Du,Weihong Xing,Wanqin Jin 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.6

Coupling nanocatalysis with ceramic membrane separation can solve the problem of nanocatalyst separation in situ from a reaction mixture. A submerged hybrid system combining nanocatalysis and ceramic membrane separation was designed for the liquid phase hydrogenation of p-nitrophenol to p-aminophenol, and the effect of initial solution apparent pH (pHa) on the performance of submerged hybrid system was investigated in detail. It is demonstrated that as the initial solution pHa is adjusted from 4.5 to 7.5, the catalytic stability of nano-sized nickel is remarkably improved, possibly because the formation of impurity on the nickel surface can be restrained at weak alkaline condition, while the catalytic activity and selectively almost do not change. The membrane permeability is not affected significantly by the initial solution pHa .

Preparation and properties of sulfated zirconia for hydrolysis of ethyl lactate

Weixing Li,Yingxiang Ni,Weiwei Liu,Weihong Xing,Nanping Xu 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.6

Sulfated zirconia catalysts are proposed for the reversible hydrolysis of ethyl lactate instead of liquid acids. Sulfated zirconia catalysts were prepared by precipitation-impregnation method. The zirconium hydroxide was produced from zirconium oxychloride by adding aqueous ammonia and then impregnated in sulfuric acid. The solid samples were obtained by filtration and evaporation of the mixtures, respectively. After the samples were calcined, the sulfated zirconia catalysts were prepared. The results showed that the catalyst prepared by evaporation has higher catalytic activity. The physicochemical characteristics of the sulfated zirconia catalysts were studied by thermal analysis, X-ray powder diffraction (XRD), temperature programmed desorption of ammonia (NH3-TPD) and N2 adsorption-desorption,respectively. By the precipitation-impregnation-evaporation method, the optimal sulfated zirconia catalyst of tetragonal phase was prepared under liquid-solid ratio of 5ml/g, 1 mol/L of H2SO4 and calcination at 650 oC for 3 h. The conversion of the ethyl lactate was 87.8% in 3 h at 85 oC with the catalyst loading 2 wt% and initial molar ratio of water to ethyl lactate 20 : 1.

Preparation and characterization of chitosan-poly (vinyl alcohol)/polyvinylidene fluoride hollow fiber composite membranes for pervaporation dehydration of isopropanol

Jing Wang,Wenying Zhang,Weixing Li,Weihong Xing 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.7

A new hollow fiber composite membrane of chitosan-poly (vinyl alcohol)/polyvinylidene fluoride (CSPVA/ PVDF) was prepared by casting the solution of CS and PVA on PVDF hollow fiber support for pervaporation dehydration of isopropanol. The composite membranes were crosslinked with glutaraldehyde (GA) and sulfuric acid. The microstructure and physicochemical properties of the membranes were characterized by scanning electron microscope (SEM), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), thermogravimetry (TG) and contact angle measurements. Results from SEM images showed that dense separation layers were successfully coated onto the supports, and the ATR-FTIR results showed that GA had crosslinked the composite membranes. Results of TG and contact angle showed the thermostability of membranes increased and the hydrophilicity decreased after blending CS and PVA. The swelling degree of composite membranes increased with increasing CS content and water content. Effects of the content of CS and GA in solution on membrane separation performance were investigated. The pervaporation experiments for dehydration of isopropanol showed that the membrane with 60 wt% CS and 0.1 wt% GA had a good separation performance. The permeate flux was 306 g/(m2·h) and the separation factor was 2140 for the feed solution containing 90% isopropanol at 60 oC. When the water content increased from 3 wt% to 15 wt%, the permeate flux increased from 207 g/(m2·h) to 346 g/(m2·h) while the separation factor decreased from 2406 to 1876. The separation factor and permeation flux increased with feed temperature.

Continuous phenol hydroxylation over ultrafine TS-1 in a side-stream ceramic membrane reactor

Rizhi Chen,Xiulong Jiang,Fei She,Hong Jiang,Weihong Xing,Wanqin Jin 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.4

A side-stream ceramic membrane reactor system was developed that can facilitate the in situ separation of ultrafine catalysts from the reaction mixture and make the production process continuous. Continuous hydroxylation of phenol to dihydroxybenzene over ultrafine titanium silicalites-1 (TS-1) was taken as a model reaction to evaluate the feasibility and performance of the membrane reactor system. The effects of membrane pore size and operation conditions (residence time, temperature, catalyst concentration, phenol/H2O2 molar ratio) on the performance of the reactor system were examined via single factor experiments. We demonstrated that the membrane pore size and operation conditions greatly affect the conversion, selectivity and filtration resistance. The phenol conversion and dihydroxybenzene selectivity remain stable at about 11% and 95% in a 20-h continuous run, respectively.

Pd nanoparticles supported on N-doped porous carbons derived from ZIF-67: Enhanced catalytic performance in phenol hydrogenation

Shuaishuai Ding,Chunhua Zhang,Yefei Liu,Hong Jiang,Weihong Xing,Rizhi Chen 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.46 No.-

We reported a Pd@CN catalyst made of Pd nanoparticles supported on a N-doped carbon derived fromZIF-67. The CN materials with micro/mesoporous structures were well developed for the loading of Pdnanoparticles and improving the catalytic performances. With the increase of calcination temperature ofZIF-67, the BET surface of CN materials initially increased and then reduced. Moreover, the highercalcination temperature would lead to lower nitrogen content in CN materials, causing lower selectivityof phenol hydrogenation to cyclohexanone. Our Pd@CN600 catalyst achieved a conversion of ca. 95% and aselectivity of ca. 95%, and exhibited excellent stability during recycling experiments

"Insights into deactivation mechanism of Pd@CN catalyst in the liquid-phase hydrogenation of phenol to cyclohexanone"

Rizhi Chen,Shuo Hu,Xiang Zhang,Zhengyan Qu,Hong Jiang,Yefei Liu,Jun Huang,Weihong Xing 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.53 No.-

"The deactivation mechanism of Pd@CN catalyst in the liquid-phase phenol hydrogenation was investigated by designing many experiments. The phenol conversion decreased by 40% through five reaction cycles. The catalyst deactivation could be mainly ascribed to the surface coverage and the pore blockage with organic matters including cyclohexanone and other derivatives. Three after-treatment methods, i.e., water washing, drying and storing in water, strongly affected the catalytic activity of Pd@CN. After the reaction, by storing the recovered Pd@CN catalyst in water, its catalytic performance could be maintained. These findings provide in-depth insights on the deactivation and recycling of Pd@CN catalyst."