Xiangui Yang

Hydrated Alkali Metal Halides as Efficient Catalysts for the Synthesis of Cyclic Carbonates from CO2 and Epoxides

The synthesis of propylene carbonate from carbon dioxide and propylene oxide using hydrated alkali metal halides as catalysts in the absence of a co-catalyst and a solvent was investigated. The hydrated alkali metal halides showed much higher catalytic activity than the anhydrous alkali metal halides. Sodium iodide dihydrate was found to be the most efficient among them and it gave a 97% yield of propylene carbonate at 120 °C under 1 MPa within 1.5 h. The corresponding cyclic carbonates from CO2 and other epoxides using sodium iodide dihydrate as catalyst were also successfully synthesized.

Synthesis of Propylene Carbonate from Carbon Dioxide and o-Chloropropanol

Abstract A new route of synthesis of propylene carbonate from carbon dioxide and o -chloropropanol was studied. Catalytic activity of several inorganic solid bases and an organic amine was compared for the reaction. The results show that potassium carbonate and triethylamine both exhibit high activity. The catalytic system of K 2 CO 3 -N(Et) 3 has higher propylene carbonate yield than that of either K 2 CO 3 or N(Et) 3 itself. Under the optimal reaction conditions, 98% o -chloropropanol conversion and 95% propylene carbonate selectivity were obtained on K 2 CO 3 -N(Et) 3 .

One-pot synthesis of high-molecular-weight aliphatic polycarbonates via melt transesterification of diphenyl carbonate and diols using Zn(OAc)2 as a catalyst

A simple and efficient route for one-pot synthesis of high-molecular-weight aliphatic polycarbonates (APCs) by direct melt transesterification of diphenyl carbonate (DPC) with aliphatic diols at equimolar amounts was developed. Zn(OAc)2 was found to be the best catalyst for this reaction among the screened transition metal acetates. The effects of reaction conditions on Mw and yield of the poly(1,4-butylene carbonate) (PBC) were investigated, where the highest Mw of 156200 g mol−1 with a yield of 83% was obtained under suitable reaction conditions. In addition, based on the results of thermogravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR), a plausible reaction mechanism over Zn(OAc)2 was proposed for APC synthesis.

Molybdenum Trioxide Catalyst for Transesterification of Dimethyl Carbonate and Phenyl Acetate to Diphenyl Carbonate

Abstract A molybdenum trioxide catalyst for the transesterification of dimethyl carbonate (DMC) and phenyl acetate (PA) to diphenyl carbonate (DPC) was prepared by the calcination method. The effect of calcination temperature and recycling of the catalyst were investigated. The catalyst prepared at 400 or 500 °C showed the highest activity, with a DMC conversion of 73.9%, and the selectivity for DPC and MPC was 39.5% and 56.5%, respectively. The catalyst activity fell and the conversion of DMC was reduced from 73.9% to 10.2% after five recycles. X-ray diffraction showed that the catalyst had an orthorhombic structure and the (110) or/and (021) face(s) is/are the most active for the transesterification of DMC and PA. The used catalyst can be easily regenerated by calcination at 400 or 500 °C in air for 5 h, and the catalytic activity of the regenerated catalyst was almost as high as the fresh one.

Magnesium acetate used as an effective catalyst for synthesizing aliphatic polycarbonates via melt transesterification process

High-molecular-weight aliphatic polycarbonates(APCs) were synthesized through a two-step transesterification process under solvent-free conditions. Oligomers with equal numbers of hydroxyl and phenyl carbonate terminal groups could be easily controlled by using equimolar amounts of diphenyl carbonate(DPC) and aliphatic diols as feedstocks in the first step. In the second step, the high-molecular-weight APCs can be obtained by connecting ―OH with OC(O)OC6H5 end-group upon removing the generated phenol at reduced pressure. Mg(OAc)2 was found to be the best catalyst for this process among the screened catalysts, which gave the poly(1,4-butylene carbonate)(PBC) a weight-average molecular weight(Mw) of 148600 and a yield of 84.8% under its suitable reaction conditions. In addition, based on the results of X-ray diffraction(XRD), scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR), a possible reaction mechanism over Mg(OAc)2 was proposed for APCs synthesis.

Transesterification of dimethyl oxalate with phenol over a MoO3/SiO2 catalyst prepared by thermal spreading

Abstract MoO3/SiO2 catalysts for the transesterification of dimethyl oxalate (DMO) with phenol were prepared by both the thermal spreading (TS) and incipient wetness impregnation methods. The results showed that the 10%MoO3/SiO2 catalyst prepared by TS (10%MoO3/SiO2-TS) exhibited higher catalytic performance compared with the 10%MoO3/SiO2 catalyst prepared by incipient wetness impregnation (10%MoO3/SiO2-C). The catalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, pyridine-IR spectroscopy, and NH3 temperature- programmed desorption. These analyses indicated that weak Lewis acid sites were formed on the catalyst surfaces and that the Mo species were present as monomeric MoO3 rather than as isolated molybdenum oxide or polymolybdate species on both catalysts, although the 10%MoO3/SiO2-TS exhibited better dispersion of MoO3 and a higher surface Mo content than the 10%MoO3/SiO2-C. Under the optimal transesterification reaction conditions (1.2 g 10%MoO3/SiO2-TS, T = 180 °C, n(DMO)/n(phenol) = 2, t = 4 h), the conversion of phenol was 70.9%, and the yields of methyl phenyl oxalate and diphenyl oxalate were 63.1% and 7.7%, respectively.

Solvent-free thermal decomposition of methylenediphenyl di(phenylcarbamate) catalyzed by nano-Cu2O

Methylene di(phenylisocyanate) (MDI) was prepared by thermal decomposition of methylenediphenyl di(phenylcarbamate) (MDPC) under solvent-free conditions with a nano-Cu2O catalyst. The preparation of nano-Cu2O was investigated in detail to obtain the optimal catalytic performance. The thermal decomposition reaction conditions, including reaction temperature, reaction pressure, and reaction time, were studied in the presence of nano-Cu2O. The results show that Cu2O prepared using a hydrolysis method and then calcined at 300 °C in Ar atmosphere for 2 h exhibited the optimal catalytic activity. The optimal reaction conditions were as follows: mass ratio of catalyst to MDPC 6.0 × 10−4, reaction temperature 220°C, reaction time 12 min, and reaction pressure 0.6 kPa. Under these conditions, the conversion of MDPC reached 99.8% and 86.2% MDI selectivity was achieved.

Structure-activity correlations of calcined Mg-Al hydrocalcites for aliphatic polycarbonate synthesis via transesterification process

Mg-Al mixed oxides with different Mg/Al molar ratio were prepared by thermal decomposition of hydrotalcitelike precursors at 500 °C for 5.0 h and used as catalysts for the transesterification of diphenyl carbonate with 1,4-butanediol to synthesize high-molecular-weight poly(butylene carbonate) (PBC). The structure-activity correlations of these catalysts in this transesterification process were discussed by means of various characterization techniques. It was found that the chain growth for the formation of PBC can only be obtained through connecting ―OH and ―OC(C)OC6H5 end-group upon removing the generated phenol, and the sample with Mg/Al molar ratio of 4.0 exhibited the best catalytic performance, giving PBC with Mw of 1.64 × 105 g/mol at 210 °C for 3.0 h. This excellent activity depended mainly on the specific surface area and basicity rather than pore structure or crystallite size of MgO.

Preparation of polycarbonate diols (PCDLs) from dimethyl carbonate (DMC) and diols catalyzed by KNO3/γ-Al2O3

γ-Al2O3 loaded with potassium nitrate (KNO3/Al2O3) catalysts were prepared, characterized and employed as a type of heterogenous solid base catalyst in the synthesis of polycarbonate (1,4-butane carbonate)-diol (PBC–OH) via the transesterification of dimethyl carbonate (DMC) and 1,4-butanediol (BD). The relationship between physicochemical properties and catalytic performance for KNO3/Al2O3 in this transesterification reaction was investigated using various techniques. The results demonstrated that the performance of KNO3/Al2O3 catalysts was highly influenced by basic site amount and strength. The medium and strong basic sites were beneficial for this reaction. The catalyst with a KNO3 loading of 35% and a calcination temperature of 700 °C exhibited the best catalytic activity due to its highest basic site amount and appropriate base strength. The highest BD conversion and PBC–OH yield of 80.2% and 68.4% were obtained under optimal reaction conditions. Also, this solid base catalyst was successfully employed in the synthesis of copolycarbonate diols from DMC and two different diols. Different scanning calorimetry results indicated that the thermal properties of the copolycarbonate diols can be adjusted by regulating the average segment lengths, Mn and copolymer composition structure.