Xinqiang Zhao

Characterization of catalyst in the synthesis of dimethyl carbonate by gas-phase oxidative carbonylation of methanol☆

Abstract The bulk and surface properties of PdCl2–CuCl2–CH3COOK catalysts supported on activated carbon (a.c.) used in the synthesis of dimethyl carbonate (DMC) by gas-phase oxidative carbonylation of methanol were characterized by XRD and XPS techniques. On the basis of the catalyst characterization and evaluation results, the active species of the catalyst has been suggested, and the reaction mechanism of oxidative carbonylation has been proposed. The interaction between CH3COOK and PdCl2 or CuCl2 on the activated carbon support has been deduced from the formation of KCl, and the partial reduction of CuCl2–CuCl has been found. Furthermore, the presence of CuCl2 inhibits the reduction of PdCl2. The experimental results show that the main reason for catalyst deactivation could be attributed to the loss of chlorine. Fortunately, promoter CH3COOK could inhibit the loss of chlorine, and improve the electronic environment of PdCl2–CuCl2 catalyst, so that the stability and activity of the catalyst PdCl2–CuCl2–CH3COOK/a.c. increase.

Direct synthesis of 2-ethylhexanol via n-butanal aldol condensation–hydrogenation reaction integration over a Ni/Ce-Al2O3 bifunctional catalyst

Direct synthesis of 2-ethylhexanol from n-butanal via the reaction integration of n-butanal self-condensation with 2-ethyl-2-hexenal hydrogenation is of crucial interest for industrial production of 2-ethylhexanol. Furthermore, as an important and versatile chemical, n-butanol can be produced simultaneously by reaction integration. In the present work, several bifunctional catalysts based on γ-Al2O3 were prepared by the impregnation method and were characterized by means of H2-TPR, XRD, TEM and H2-TPD, and their catalytic performance for direct synthesis of 2-ethylhexanol from n-butanal was investigated. The results showed that Co/Al2O3 had a low activity for hydrogenation and Cu/Al2O3 had a high selectivity for the hydrogenation of the CO group while a Ru/Al2O3 catalyst only favored the hydrogenation of n-butanal to n-butanol. Among them, the Ni/Al2O3 catalyst showed the best catalytic performance and the yield of 2-ethylhexanol was the highest (49.4%). Ce-modified Ni/Al2O3 enhanced the competitiveness of aldol condensation versus hydrogenation of n-butanal and improved the selectivity of 2-ethylhexanol; the yield of 2-ethylhexanol rose to 57.8%. Then the influence of preparation conditions on the catalytic performance of Ni/Ce-Al2O3 was investigated and the suitable preparation conditions were obtained as follows: Ni loading = 10%, calcined at 550 °C for 5 h, and reduced at 570 °C for 4 h. The effect of reaction conditions on the integration reaction catalyzed by Ni/Ce-Al2O3 was investigated and the suitable reaction conditions were obtained as follows: weight percentage of Ni/Ce-Al2O3 = 15%, reaction temperature = 170 °C, reaction pressure = 4.0 MPa and reaction time = 8 h. Under the above reaction conditions, the yield of 2-ethylhexanol attained 66.9% and that of n-butanol was 18.9%. In addition, the components existing in the integration reaction system were identified by GC-MS analysis, and the main by-products were n-butyl butyrate, 2-ethylhexyl butyrate, n-butyric acid, etc. Based on the analysis of the reaction system, a reaction network for the direct synthesis of 2-ethylhexanol from n-butanal was proposed. Finally, an evaluation of the reusability of Ni/Ce-Al2O3 showed that the recovered Ni/Ce-Al2O3 catalyst lost its catalytic activity for the hydrogenation of the CO group. The main reason for deactivation was that Ni species were covered by the flaky boehmite γ-AlO(OH) formed from the hydration of γ-Al2O3 in the reaction process.

Catalysis by Lead Oxide for Diethyl Carbonate Synthesis from Ethyl Carbamate and Ethanol

Abstract The catalysis by lead oxide in the reaction of ethyl carbamate (EC) with ethanol to form diethyl carbonate (DEC) was studied. The lead oxide catalyst exhibited an excellent stability, which could be reused five times without a significant loss in catalytic activity. X-Ray powder diffraction analysis showed that the recovered catalyst was a mixture of cubic metal Pb and orthorhombic PbO2, with the latter shown to be the real active component for the synthesis of DEC. Verification experiments showed that the reaction between DEC and PbO was the main reason for the reduction of PbO to metal Pb.

Preparation of SAPO-5 and Its Catalytic Synthesis of p-Aminophenol

Abstract Silicoaluminophosphate molecular sieves (SAPO-5) were synthesized by hydrothermal crystallization using both a conventional aqueous medium and a HF medium. The SAPO-5 samples were characterized by X-ray diffraction, scanning electron microscopy, solid state NMR, Fourier transform infrared reflectance spectroscopy, and temperature-programmed desorption of adsorbed NH3. The effect of Si content and presence of HF in the initial gel on the structure of the SAPO-5 synthesized and the manner of Si incorporation into the framework were investigated. Their acidity and catalytic activity for phenylhydroxylamine (PHA) rearrangement in the synthesis of p-aminophenol (PAP) from nitrobenzene were studied. The incorporation of Si in the samples prepared in the presence of HF was mainly by the SM3 mechanism and patches of Si(4Si) were predominant. This resulted in a decrease in the acid amount and increase in acid strength. The presence of HF during synthesis increased the integrity of the SAPO-5 crystal and helped incorporate more Si in the SAPO-5 structure by inhibiting the polymerization of Si species to a reticulated silica gel. The samples prepared in the HF medium exhibited better catalytic performance for PHA rearrangement in the synthesis of PAP, and a PAP yield of 53.2% could be obtained.

Synthesis of 4,4′-MDC in the Presence of Sulfonic Acid-functionalized Ionic Liquids

Abstract The synthesis of methylene diphenyl dimethylcarbamate (4,4′-MDC) from methyl N -phenyl carbonate (MPC) and formaldehyde (HCHO) was conducted in the presence of sulfonic acid-functionalized ionic liquids (ILs) as dual solvent-catalyst. The influences of the kind of anion in the ionic liquids, reaction conditions and the recycle of the ionic liquid on 4,4′-MDC synthesis reaction were investigated. In addition, the acid strength of ILs was determined by the Hammett method with UV-visible spectroscopy, and the acid strength-catalytic activity relationship was correlated. The activity estimation results showed that [HSO 3 -bmim]CF 3 SO 3 was the optimal dual solvent-catalyst. Under the suitable reaction conditions of 70°C, 40 min, molar ratio of n MPC / n HCHO 10/1 and mass ratio of W ILs / W MPC 4.5/1, the yield of 4,4′-MDC based on HCHO was 89.9 % and the selectivity of 4,4′-MDC with respect to MPC was 74.9%. Besides, [HSO 3 -bmim]CF 3 SO 3 was reused four times after being purified and no significant loss in the catalytic activity was observed.

Influence of Solvent on Reaction Path to Synthesis of Methyl N-Phenyl Carbamate from Aniline, CO2 and Methanol

Abstract Methyl N -phenyl carbamate (MPC), an important organic chemical, can be synthesized from aniline, CO 2 and methanol. Catalyst Cu-Fe/ZrO 2 -SiO 2 was first prepared and its catalytic performance for MPC synthesis was evaluated. Then the influence of solvent on the reaction path of MPC synthesis was investigated. It is found that the reaction intermediate is different with acetonitrile or methanol as a solvent. With acetonitrile as a solvent, the synthesis of MPC follows the reaction path with diphenyl urea as the intermediate, while with methanol as a solvent the reaction occurs via the reaction path with dimethyl carbonate as the intermediate. The catalytic mechanism of cooperative catalysis comprising metal sites, Lewis acid sites and Lewis base sites is proposed according to different reaction intermediates.

n-Butyraldehyde self-condensation catalyzed by Ce-modified γ-Al2O3

Self-condensation of n-butyraldehyde is an important process for the industrial production of 2-ethylhexanol. The catalytic performance of some solid acids such as γ-Al2O3 and molecular sieves for the self-condensation of n-butyraldehyde was investigated and the results showed that γ-Al2O3 was the best one. Then the effect of preparation conditions on the catalytic performance of γ-Al2O3 and the effect of reaction conditions on the self-condensation of n-butyraldehyde were discussed. In order to improve the catalytic performance, γ-Al2O3 was modified by different substances and Ce–Al2O3 was found to show the best catalytic performance; the conversion of n-butyraldehyde and the yield of 2-ethyl-2-hexenal could reach 93.8% and 88.6%, respectively. Moreover, the Ce–Al2O3 catalyst had excellent reusability. The XPS analysis of Ce3d demonstrated that the valence state of cerium affected the catalytic performance of Ce–Al2O3 to some extent but not predominantly. Instead the acid–base property of Ce–Al2O3 played a dominant role in the catalytic performance. The reaction components formed over the Ce–Al2O3 catalyst were identified by GC-MS and then some side-reactions were speculated and a reaction network for n-butyraldehyde self-condensation catalyzed by Ce–Al2O3 was proposed. Subsequently, the research on the intrinsic kinetics of n-butyraldehyde self-condensation catalyzed by Ce–Al2O3 showed that both the forward and backward reactions are second order and the corresponding activation energy is separately 79.60 kJ mol−1 and 74.30 kJ mol−1, which is higher than that of the reaction catalyzed by an aqueous base or acid.

Reactivity of hydroxylamine ionic liquid salts in the direct synthesis of caprolactam from cyclohexanone under mild conditions

The reactivity of several sulfobutyl hydrosulfate hydroxylamine ionic liquid salts in the direct synthesis of caprolactam from cyclohexanone under mild conditions was investigated. The results showed that the cyclohexanone conversion was mainly affected by cation species in the molecules of the hydroxylamine ionic liquid salts, and hydroxylamine N,N,N-trimethyl-N-sulfobutyl hydrosulfate salt was a better choice for the direct synthesis of caprolactam. The optimum reaction condition was at 80 °C for 4 h, and the suitable molar ratio of cyclohexanone : hydroxylamine ionic liquid salt : ZnCl2 was 2 : 1 : 3. Under the optimal reaction conditions, cyclohexanone was almost completely converted into caprolactam, corresponding to 99.1% cyclohexanone conversion and 92.0% caprolactam selectivity. Furthermore, the reaction medium acetonitrile, and the ionic liquid which was combined in the hydroxylamine salt, can be recovered after the reaction, achieving an eco-friendly route for the direct synthesis of caprolactam.

Synthesis of Toluene-2,4-Bisurea from 2,4-Toluene Diamine and Urea and the Reaction Kinetics

Abstract Toluene-2,4-bisurea (TBU) is an important intermediate for urea route to dimethyl toluene-2,4-dicarbamate and the study on TBU synthesis via the reaction of 2,4-toluene diamine (TDA) and urea is of great significance. Firstly, thermodynamic analysis shows that the reaction is exothermic and a high equilibrium conversion of TDA is expected due to its large reaction equilibrium constant. Secondly, under the suitable reaction conditions, 130 °C, 7 h, and molar ratio of TDA/zinc acetate/urea/sulfolane=1/0.05/3.5/10, TDA conversion is 54.3%, and TBU yield and selectivity are 39.8% and 73.3% respectively. Lastly, the synthesis of TBU is a 1st order reaction with respect to TDA and the reaction kinetics model is established. This work will provide useful information for commercializing the urea route to toluene-2,4-dicarbamate (TDC).