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Totally found 204 items.

  • [期刊] Phenylsulfonic Acid Functionalized Mesoporous Silica Catalyzed Transetherification of Alcohols with Dimethoxymethane
    Phenylsulfonic acid functionalized mesoporous silica was synthesized by condensation of tetraethylorthosilicate with phenyltrimethoxysilane, and then sulfonation using 30% fuming sulfuric acid. The material was characterized using FT-IR, DSC, XPS, TEM and N2 adsorption/desorption measurements. DSC revealed that sulfonic acid group of the catalyst was decomposed at 354.8℃, indicating that the catalyst exhibited high thermal stability. XPS showed that there existed three kinds of different silicon species on surface of the catalyst. The catalytic performance of the catalyst was evaluated using transetherification of alcohols with dimethoxymethane. It was found that among primary alcohols, the selectivities of the two long-chain alcohols for n-dedocanol and n-tetradecyl alcohol were higher than 97.0% at the conversions of 43.6% and 65.3%, respectively, while the selectivities of the short-chain alcohols except for n-hexanol were less than 90.0% at the conversions of over 80.0%. Due to steric bartier, the secondary alcohols such as /so-butanol and cyclohexanol afforded conversions of 79.4% and 60.5%, and the selectivities of the two alcohols were more than 90.0%. The sequence in conversion of the substituted phenols isas follows: p-nitrophenol>p-fluorophenol≥p-bromophenol>p-cresol>m-cresol.
  • [期刊] 甲缩醛与甲酸偶联合成甲氧基乙酸甲酯
    在釜式反应器中研究了甲缩醛与甲酸偶联生成甲氧基乙酸甲酯的反应.测试了几种催化剂的催化性能,并选定对甲苯磺酸催化剂作进一步的实验研究.考察了反应温度、反应时间、原料配比、催化剂用量等对甲氧基乙酸甲酯收率的影响,确定最佳反应条件为:n(甲缩醛)∶n(甲酸)=0.36,催化剂用量为甲缩醛质量的1.8%,反应温度140℃,反应时间4h.在此条件下,甲氧基乙酸甲酯的收率为87.1%.
  • [期刊] Detailed kinetic modeling of dimethoxymethane. Part Ⅱ: Experimental and theoretical study of the kinetics and reaction mechanism
    In this study (Part II), the oxidation of dimethoxymethane (DMM) is investigated and a detailed chemical reaction model developed for a comprehensive description of both high- and low-temperature oxidation processes. The sub-mechanism of DMM is implemented using AramcoMech2.0 as the base mechanism. Rate coefficients are based on analogies with those for dimethyl ether, diethyl ether, and n-pentane oxidation. Furthermore, theoretical studies from recent works are also included in the present model and new calculations for the dissociation kinetics of (Q) over dotOOH radicals have been carried out at the CCSD(T)/CBS(aug-cc-pVXZ; X=D, T) // B2PLYP-D3/6-311 + + G(d,p) level of theory. For validation, new ignition delay time experiments have been performed in a shock tube (ST), a rapid compression machine (RCM), and in a laminar flow reactor covering a wide range of conditions (p = 1-40 bar, T= 590-1215 K, phi = 1). In addition, the kinetic model is validated against laminar burning velocities, jet-stirred reactor, plug flow reactor and further ST and RCM experimental datasets from the literature. Pathway and sensitivity analyses were used to identify critical reaction pathways in the DMM oxidation mechanism. These show that the reactivity of DMM at intermediate temperatures is controlled by the branching between pathways initiated on the primary or secondary fuel radical. While primary fuel radicals eventually lead to chain branching, secondary fuel radical consumption is controlled by fast beta-scission over a wide range of temperatures, which inhibits reactivity. (C) 2018 Published by Elsevier Inc. on behalf of The Combustion Institute.
  • [期刊] Effect Of Crystallinity In HZSM-5-Amorphous Alumosilica Systems On Their Catalytic Properties In The Synthesis Of Dimethoxymethane
    Granulated catalysts with 3-5% H-ZSM-5 phase were obtained from a highly dispersed alumosilica and were used for the synthesis of dimethoxymethane (DMM) from methanol and formaldehyde. The activity of these catalysts is greater than the activity of pure zeolite. A linear correlation was found between the yield of DMM and the content of Bronsted acid sites in the catalysts.
  • [期刊] Promotional effects of Sm2O3 on Mn-H4SiW_(12)O_(40)/SiO2 catalyst for dimethyl ether direct-oxidation to dimethoxymethane
    The promotional effects of Sm2O3 on Mn-H4SiW_(12)O_(40)/SiO2 for dimethyl ether (DME) direct-oxidation to dimethoxymethane (DMM) were investigated. The results showed that Sm2O3 introduction could significantly improve the activity of Mn-H4SiW_(12)O_(40)/SiO2 for DMM formation, and DMM selectivity was remarkably increased from 36.3% to 60.3% when the Sm2O3 content was 1%. The catalysts were characterized by 1CP-AES, XRD, NH3-TPD, Pyridine-IR and XPS. The Sm2O3 introduction enhanced the number of Lewis acid sites and weak acid sites and also increased the amount of Mn~(4+) species of Mn-H4SiW_(12)O_(40)/SiO2, which is favorable for the formation of DMM.
  • [期刊] Surface tension of dimethoxymethane and methyl tert-butyl ether
    The surface tension of dimethoxymethane was measured at temperatures from (238 to 388) K with a differential capillary rise method (DCRM), together with the surface tension of methyl tert-butyl ether measured at temperatures from (243 to 393) K. The uncertainty of temperature is less than +/- 10 mK (ITS-90). The uncertainty of surface tension measurements was estimated to be within +/- 0.2 mN, m(-1). The results were correlated as a function of temperature, and the average absolute deviations were 0.059 mN, m(-1) for dimethoxymethane and 0.050 mN, m(-1) for methyl tert-butyl ether, respectively.
  • [期刊] Conversion from Dimethyl Ether to Dimethoxymethane and Dimethoxyethane Using Dielectric-Barrier Discharge Plasma
    Experimental investigation was conducted to convert dimethyl ether (DME) in the presence of steam using dielectric barrier discharge (DBD) at atmospheric pressure and 373 K. The flow rate of DME was 20 ml/min. The introduction of steam resulted in an increase in the DME conversion and the selectivity of oxygenates. Plasma steam-enhanced dimethyl ether (DME) conversion led to a direct synthesis of DMMT and DMET, with a high selectivity of 5.78% and 17.99%, respectively. The addition of steam promoted the formation of "plasma aerosol" that was favored for the formation of liquid oxygenates. The reaction pathway of plasma DME conversion was proposed.
  • [期刊] Direct Measurement of High-Temperature Rate Constants of the Thermal Decomposition of Dimethoxymethane, a Shock Tube and Modeling Study
    Shock-tube experiments have been performed to investigate the thermal decomposition of the oxygenated hydrocarbon dimethoxymethane (DMM; CH3OCH2OCH3). The primary initial reaction channels of DMM decomposition are considered to be the two bond fissions: CH3OCH2OCH3 -> CH3O + CH2OCH3 (1) and CH3OCH2OCH3 -> CH3 + OCH2OCH3 (2). In the present work, two shock-tube facilities and three different detection techniques have been combined: Behind reflected shock waves, we have carried out time-resolved measurements of (i) the formation of H atoms using the highly sensitive H-ARAS (Atomic Resonance Absorption Spectrometry) technique and (ii) the depletion of the DMM reactant by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS). In addition, (iii) the temperature-dependent composition of stable reaction products was measured in single-pulse shock-tube experiments via gas chromatography (GC/MS). The experiments span a temperature range of 1100-1430 K, a pressure range of 1.2-2.5 bar, and initial reactant mole fractions from 0.5 ppm (for H-ARAS experiments) up to 10 000 ppm (for HRR-TOF-MS experiments). Experimental rate constants k(total), k(total) = k(1) + k(2), obtained from these three completely different methods were in excellent agreement among each other, i.e., deviations are within +/- 30-40%, and they can be well represented by the Arrhenius expression k(total)( T) = 10(13.28 +/- 0.27) exp(-247.90 +/- 6.36 kJ mol(-1)/ RT) s(-1) (valid over the 1100-1400 K temperature and the 1.2-2.5 bar pressure range). By replacing the respective ktotal values used in a recently published DMM chemical kinetics combustion mechanism (Vermeire et al. Combust. Flame 2018, 190, 270-283), it was also possible to successfully reproduce measured product distributions.
  • [期刊] Density and viscosity of saturated liquid dimethoxymethane from (218.15 to 383.15) K
    The density and viscosity of saturated liquid dimethoxymethane were measured over the temperature range from (218.15 to 383.15) K with a vibrating-tube densimeter and a calibrated Ubbelohde-type capillary viscometer, respectively. The estimated uncertainties of the measurements were 1.0 kg/m(3) for density and ± 1.8% for viscosity. Density results were fitted using the polynomial with an absolute average deviation of 0.13% and a maximum deviation of 0.22% from the correlated equation. Viscosity results were correlated as a function of temperature. The absolute average deviation and the maximum deviation of the experimental viscosity results from the correlated equation are 0.45% and 1.07%, respectively.
  • [期刊] Direct Measurement of High-Temperature Rate Constants of the Thermal Decomposition of Dimethoxymethane, a Shock Tube and Modeling Study
    Shock-tube experiments have been performed to investigate the thermal decomposition of the oxygenated hydrocarbon dimethoxymethane (DMM; CH3OCH2OCH3). The primary initial reaction channels of DMM decomposition are considered to be the two bond fissions: CH3OCH2OCH3 -> CH3O + CH2OCH3 (1) and CH3OCH2OCH3 -> CH3 + OCH2OCH3 (2). In the present work, two shock-tube facilities and three different detection techniques have been combined: Behind reflected shock waves, we have carried out time-resolved measurements of (i) the formation of H atoms using the highly sensitive H-ARAS (Atomic Resonance Absorption Spectrometry) technique and (ii) the depletion of the DMM reactant by high-repetition-rate time-of-flight mass spectrometry (HRR-TOF-MS). In addition, (iii) the temperature-dependent composition of stable reaction products was measured in single-pulse shock-tube experiments via gas chromatography (GC/MS). The experiments span a temperature range of 1100-1430 K, a pressure range of 1.2-2.5 bar, and initial reactant mole fractions from 0.5 ppm (for H-ARAS experiments) up to 10 000 ppm (for HRR-TOF-MS experiments). Experimental rate constants k(total), k(total) = k(1) + k(2), obtained from these three completely different methods were in excellent agreement among each other, i.e., deviations are within +/- 30-40%, and they can be well represented by the Arrhenius expression k(total)( T) = 10(13.28 +/- 0.27) exp(-247.90 +/- 6.36 kJ mol(-1)/ RT) s(-1) (valid over the 1100-1400 K temperature and the 1.2-2.5 bar pressure range). By replacing the respective ktotal values used in a recently published DMM chemical kinetics combustion mechanism (Vermeire et al. Combust. Flame 2018, 190, 270-283), it was also possible to successfully reproduce measured product distributions.
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