Catalyst selection and thermal kinetics of oligomeric PGA depolymerization process
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Several metal oxides and their salts are used as catalysts to study the depolymerization of polyglyolic acid( PGA) oligomers. It is found that the temperature of depolymerization reaction decreases obviously under the catalysis of Zn( acac)2. At the same time,the coking is reduced in the process of preparing glycolide with the improved yield of glycolide. Zn( acac)2is also applied in the solution depolymerization of PGA,and thermal degradation of the azeotropic solvent is prevented at high temperature. It proves that Zn( acac)2can enhance the efficiency of depolymerization and the higher catalytic activity is thought to correlate to the coordination-insertion mechanism. The experimental results show that PGA oligomer is depolymerized at lower temperature( 200℃) under Zn( acac)2catalyst with a mass fraction of 0. 4%.The yield of glycolide reaches 95%. The activation energy value in process of oligomer depolymerization is lower in the presence of Zn( acac)2than the other catalysts,enhancing the efficiency of depolymerization.Keywords:
Depolymerization
Oligomer
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Depolymerization
Hydrogenolysis
Oligomer
Thermal Stability
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Propylene oxide
Propylene carbonate
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Abstract A chitosan‐supported palladium catalyst was prepared by immobilization of palladium on glutaraldehyde crosslinked chitosan followed by in situ chemical reduction. This catalyst was successfully used for the degradation of 4‐nitroaniline (4‐NA) in the presence of sodium formate, used as the hydrogen donor. The reaction product was 1,4‐phenylenediamine. The degradation was favored by acidic pH. A 10 to 15 excess of formate (compared to 4‐NA) is required to achieve complete degradation of the substrate. The reaction appears to be limited to the external layers of the catalyst: small particle size is required to optimize the degradation kinetics. Alternatively, an increase of catalyst dosage is required to increase kinetic rates but at the expense of palladium consumption. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1634–1642, 2004
Sodium formate
Degradation
Glutaraldehyde
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Abstract The efficiency of organometal‐ (Ti, Zr, Sn, Hf, and Bi) and metal oxide‐ (Ge and Sb) based catalysts was investigated during the transesterification step of the synthesis of poly(butylene succinate) (PBS). PBS was prepared from succinic acid and 1,4‐butanediol via a two‐stage melt polycondensation process. The catalytic efficiency of the organometal catalysts was as follows: Ti≫Zr∼ Sn>Hf>Sb>Bi. The germanium and antimony metal oxides displayed desirable catalytic efficiency when were associated with hydroxy acids (lactic acid or glycolic acid), which acted as chelating agents. However, this catalytic system exhibited lower efficiency compared to the titanium system. Furthermore, at high concentrations of hydroxy acids the overall transesterification rate decreased. This effect can be explained by the substitution of PBS hydroxyl end groups by a lactic or glycolic unit, both of which are less reactive during the transesterification reaction. The role of catalytic residues during the storage and processing of PBS was also studied. The reduced viscosity of the PBS samples did not vary when processing at 190 °C from 1 to 10 minutes. However, when stored under ambient conditions, all PBS samples were prone to significant hydrolytic degradation, especially those containing a titanium catalyst. This behavior indicates that zirconium‐ and germanium‐based catalysts could be interesting substitutes for titanium‐based catalysts. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.
Glycolic acid
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Induction period
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Sodium salt
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Abstract Grain poly(ethylene terephthalate) (PET) was depolymerized in pure water by different metal oxides, respectively. The catalytic hydrolysis product of terephthalic acid (TPA) obtained was the same with the no catalytic reaction. The depolymerization rate of PET was seriously influenced of the reaction time and temperature. Especially using stannous oxides as catalyst, with a reaction time of 210 min, a temperature of 200°C and a pressure of 200 psi, the depolymerization rate of PET increased from 59.3 to 90.9% compared with the no catalytic reaction. The morphology of the solid residue indicated that the depolymerization took place on the external surface of the PET grain in the presence of stannous oxide. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
Depolymerization
Reaction rate
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Depolymerization of nylon6 to e-caprolactam was carrid out with environmental-friendly heteropolyacid catalyst at temperatures between 553K and 603K,under different pressures of 6.4 MPa～12.8 MPa in water medium. The products of depolymerization were analysed qualitatively and quantitatively by means of infrared spectroscopy(FT-IR),thermo gravimetric(TG),liquid chromatography-mass spectrometry(LC/MS)and high performance liquid chromatography(HPLC). The results indicate that the main depolymerized product is e-caprolactam. Remnants solid product is undepolymerized nylon6 and the liquid products containe a little 6-aminocaproic acid and oligomer. The highest yield of e-caprolactam is 77.96% at 583K under 85min.Compared with no catalyst,the depolymerization rate and yield of e-caprolactam is high under catalytic condition. Temperature and time also have important effect on depolymerization reaction. Catalytic depolymerization kinetic at different reaction conditions was studied,where the reaction activation energy was evaluated to be 77.38 kJ/mol.
Depolymerization
Caprolactam
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Solvolytic depolymerization of lignin was studied under three different catalytic conditions and explained using a schematic representation of the mechanisms.
Depolymerization
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Development of active and selective catalysts for the process of obtaining methacrylic acid and methyl methacrylate from methyl propionate, propionic acid and formaldehyde is one of important stages to industrial implementation of this process. In order to solve this problem, we designed catalysts based on oxides of boron and phosphorus that were promoted by oxides of zirconium, tungsten and bismuth with varied content of oxides. The effect of temperature was examined on the conversion of reagents, the selectivity of formation and the yield of methyl methacrylate and methacrylic acid on the created catalysts. With increasing temperature, the conversion increases, the selectivity of formation of acrylates decreases and the total yield of acrylates has the maximum. It was found that without adding methanol, the optimal catalyst by acrylates yield is the one, in which the molar ratio of the ZrO2:WO3 promoters is 0.15:0.15. The total yield of the target products at optimum temperature of 593 K is 52.3 % with the total selectivity of their formation at 96.4 % and the conversion of reagents of 54.2 %. We determined the effect of adding methanol to the reagent mixture. Adding methanol increases the ratio of products MMA/MAA, and the optimal catalyst by the total selectivity of formation of the target products is the one promoted by bismuth oxide with the molar ratio of Bi2O3/Р2О5 – 0.3, which at a temperature of 593 K provides for the selectivity of formation of acrylates of 100 % with the yield of 33 %. The maximum total singlepass yield of MMA and MAA on this catalyst at a temperature of 623 K is 51.5 %, at the total selectivity of their formation of 91.6 %. However, the share of MMA in products is lower in comparison to the catalyst, promoted by the mixture of tungsten and zirconium oxides.
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