Separation and purification of aflatoxins B1, B2, G1 and G2, and comparison of semi-synthetic aflatoxins B2 and G2 with naturally-occurring aflatoxins B2 and G2

A method is described for the isolation of highly purified aflatoxins B₁, B₂, G₁ and G₂ from extracts ofAspergillus flavus. The four aflatoxins, isolated from background impurities by rapid passage of the extracts through an acid alumina column, are separated from each other by chromatography on a silica gel column. Aflatoxins B₂ and G₂ are prepared by hydrogenation of the mixture of aflatoxins B₁, B₂, G₁ and G₂ and then separated by elution from a silica gel column with chloroform containing 0.7% ethanol. A comparison of semi-synthetic aflatoxins B₂ and G₂ with naturally-occurring aflatoxins B₂ and G₂ shows no significant difference in physical properties. Presented at the AOCS-AACC Meeting, Washington, D.C. April, 1968.     

Kinetic and diffusion study of acid-catalyzed liquid-phase alkyl formates hydrolysis

Alkyl formates are typically hydrolyzed with the aid of homogeneous catalysts, but heterogeneous catalysts provide a promising pathway for the process. The hydrolysis of alkyl formates by a solid acid catalyst, ion-exchange resin was accomplished in a batch reactor, a stirred autoclave operating isothermally at 60 °C and 90 °C with a constant initial water-to-ester molar ratio. A mathematical model, which incorporates the particle size distribution of the solid catalyst, was developed to study the kinetics and internal mass transfer effects in the porous particles and it was able to predict the concentrations in the bulk phase and inside the catalyst particles. A combined reaction–diffusion model is necessary to describe the behavior of the system. The model was able to predict well the experimental results.     

Aflatoxins B1, B2, G1, and G2: Separation and purification

Aflatoxins B₁, B₂, G₁, and G₂ have been separated on a series of chromatographic columns. Chromatography of crude products isolated from molded wheat and rice on silicic acid with washed chloroform:ethanol (99:1) gave relatively pure B₁. The rest of the column fractions containing predominantly G₁, along with B₁, B₂, and G₂, were pooled and fractionated on a Silica Gel G column. The mobile phase was washed chloroform:acetone:ethanol (97.3:2.0:0.75). Thin-layer chromatography was used to follow column development. Each of the aflatoxins was treated with either decolorizing carbon or copper carbonate to remove colored pigments, and rechromatographed on Silica Gel G. Crystalline aflatoxins were prepared from chloroform solutions by addition ofn-hexane, methanol, or ethanol. Presented at the AOCS Meeting, New Orleans, May 1967. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Solid acid-catalyzed conversion of furfuryl alcohol to alkyl tetrahydrofurfuryl ether

The acidic zeolite HZSM-5 (Si/Al = 25) achieved 58.9% selectivity of methyl furfuryl ether (MFE) and 44.8% selectivity of ethyl furfuryl ether (EFE) from etherification of furfuryl alcohol with methanol and ethanol. MFE and EFE were quantitatively hydrogenated into methyl tetrahydrofurfuryl ether (MTE) and ethyl tetrahydrofurfuryl ether (ETE) using a Raney Ni catalyst.     

甲烷无氧直接转化反应动力学研究及设计模拟

根据甲烷无氧直接转化反应机理的动力学表达式以及相关文献资料,对甲烷无氧催化反应实验数据进行处理,估算动力学模型参数。利用建立的动力学模型,在Aspen plus过程模拟软件中对甲烷无氧直接转化反应器进行分析与设计,得出合适的反应器设计温度及设计压力,对研究以及工程设计有一定的参考价值。     

Extraction partition and column chromatographic separation of aflatoxins B1 and M1

Extraction, partition and chromatographic elution characteristics of aflatoxin were studied. The novel use of aqueous dimethylsulfoxide or aqueous dimethylformamide for extraction from agricultural products was tested and found effective. Partition studies suggest advantages in analytical work of using solvent pairs in which benzene rather than (the usually employed) chloroform is used to transfer aflatoxin B₁ from primary extracts (aqueous phases). Tests of elution characteristics of aflatoxins B₁ and M₁ on silica gel columns with different developing solvents provided a basis for a procedure in which aflatoxins B₁ and M₁ of a test sample are recovered in separate eluates in which substances which interfere with TLC separation are minimized. Presented at the AOCS Spring Meeting, San Francisco, April 1969. W. Utiliz. Res. Dev. Div., ARS, USDA.     

半纤维素六碳糖转化为5-羟甲基糠醛的动力学

选取甘露糖和半乳糖两种典型半纤维素六碳糖作为模化物,考察其在水相中较宽温度（100～200℃）和时间（10～240min）范围内的降解行为。实验结果表明,较高的反应温度能提高六碳糖的转化率和5-羟甲基糠醛（HMF）的产率;在200℃时甘露糖和半乳糖生成的HMF最高产率分别为26.82%和22.86%,乙酰丙酸（LA）的产率低于3%;半乳糖因容易异构化生成塔格糖而非果糖,导致其HMF产率较低。采用六碳糖平行生成HMF和Humin,随后HMF平行生成的LA和Humin的反应模型对六碳糖降解动力学进行分析,揭示了六碳糖的类型对HMF和Humin生成机制的影响。此外,针对六碳糖生成的Humin的Van Krevelen图和FTIR谱图进行分析进一步发现,Humin是通过脱水聚合生成的呋喃环基聚合物,同时其结构特征与单糖类型紧密相关。     

食品中的黄曲霉毒素B1、B2、G1、G2的超高效液相色谱—串联质谱检测

建立用超高效液相色谱-串联质谱检测器测定食品中的黄曲霉毒素B1、B2、G1、G2的方法。样品中残留的黄曲霉毒素经过乙腈(乙腈∶水=84∶16)提取,取经过4000 r/min离心机离心过的上层清液,经装有反相离子交换吸附剂的多功能净化柱,去除脂肪、蛋白质、色素及碳水化合物等干扰物质,氮吹定容后上机至液相质谱联用仪,根据色谱图出峰时间及与之相应标物的特征离子对作对比,对黄曲霉毒素B1、B2、G1、G2定性,再根据标准系列得出的标准曲线,换算出各黄曲霉毒素的含量。     

Kinetic model of block photopolymerization of glycidyl methacrylate to high conversion

The kinetics of glycidyl methacrylate block polymerization to high conversion was experimentally investigated with variations of the photoinitiator concentration, temperature, and power of UV illumination. The kinetic curves of this polymerization process contain three characterized sections of coordinates of “conversion–time,” namely: The first one is practically linear to a conversion of ≈0.5, the second represents, by itself, the autoacceleration process, and the third presents the autodecelation process. An additional peculiarity of such a polymerization process is poor reproduction of the kinetic measurements. This reproduction does not correspond to instrumental error. Derivation of a kinetic model for block linear polymerization was done. This model is, quantitatively, in good agreement with all the data of the experimental material. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3556–3569, 2002     

Kinetic modeling of plasma methane conversion in a dielectric barrier discharge

Methane conversion by plasma offers a promising route to produce higher value-added products. As plasma reaction is a relatively complex process, kinetic modeling is necessary to obtain a general pattern of the complex interaction on the basis of chemical reaction and products. In this paper, we present a method to obtain the kinetic rate coefficient (k) from the experimental data. Although plasma reaction was classified as chemically complex interaction, the reactions showed a certain pattern of the mechanism. In pure methane injection, the decomposition of methane by plasma could initiate coupling reactions and produce C₂H₆, C₃H₈, and C₄H₁₀. Dehydrogenation of C₂H₆ into C₂H₄ and then to C₂H₂ could be clearly seen by the higher value of the reaction rate constant of C₂H_n + 2 to C₂H_n − 2. Using the rate constant values (k) obtained by this method, the pathways of the methane conversion by a dielectric barrier discharge can be drawn.     

Kinetic contribution of CO2/O2 additive in methane conversion activated by non-equilibrium plasmas

A temperature-controlled and pressure-controlled coaxial dielectric barrier discharge(DBD) reactor was developed to decouple the thermal and kinetic effects of radio frequency(RF) discharge on methane conversion,and further to compare the kinetic behaviors of the mechanistically similar reactions of methane conversion with O_2 and CO_2 additives. A kinetic mechanism for RF plasma assisted methane conversion was assembled. The formation of products in the RF plasma reactor was measured with Gas Chromatography(GC–TCD) and the data were used to validate the kinetic model. The experimental and computational results showed the different kinetic roles of carbon dioxide and oxygen additives in methane conversion, due to the different dissociation and ionization energy of the two additive gases, as well as the thus produced electron energy distribution function(EEDF). Fuel oxidation by plasma generated O, O(~1 D), O_2(a~1Δg), O_2(b~1Σ_g~+) and O+in partial oxidation of methane was observed essential for methane consumption, which resulted in an increase in methane conversion rate,compared to pure methane pyrolysis and dry reforming of methane with CO_2 additive. It was also found that dry reforming of methane with CO_2 was by far the easier to produce the syngas as well as C_2 hydrocarbon species,due to the weak oxidation ability of CO_2 and also the significant deposition of the electron energy on CH_4 dissociation in a dry reforming discharge mixture. This kinetic study produced comparative data to demonstrate the contribution of CO_2/O_2 additive in non-equilibrium plasma assisted methane conversion.     

催化氧化法处理红色基B废水的动力学研究

研究了催化氧化法处理红色基B生产过程所产生的工业废水的动力学。红色基B的工业废水COD值高达40 063 mg·L~(-1),含有大量有机物,颜色为红色且有强烈的刺激气味。废水处理过程中以FeSO_4为催化剂、H_2O_2为氧化剂,研究了催化氧化法处理废水的工艺路线及工艺条件,分析了影响因素,建立了动力学模型,研究了其催化氧化的动力学过程。结果表明,处理后的废水的COD值可降为4 mg·L~(-1)左右,去除率为90%;所建立的过氧化物催化氧化红色基B废水的动力学方程与实验数据拟合较好。其表观动力学方程为:-(dc)/(dt)=1.978 6exp(-(19 351)/(RT))[H_2O_2]_0~(0.979 6)c     

Kinetic modelling of the catalytic conversion of synthesis gas

A kinetic study for the one-step conversion of synthesis gas to gasoline on a ZnO–Cr₂O₃–ZSM-5 catalyst is described. On this catalyst, three reactions are involved in the overall transformation of synthesis gas: the methanol synthesis, the conversion of methanol to hydrocarbons and the water–gas shift reaction. Under the operating conditions selected for the study, it was found that the water–gas shift was at equilibrium and the methanol was completely converted to hydrocarbons. Consequently, it was postulated that the kinetics of the limiting reaction step, the methanol synthesis on the ZnO–Cr₂O₃ component, was the one that controls the overall reaction rate. Three kinetic model equations describing the rate of synthesis gas conversion on the bifunctional catalyst, were considered to fit the data of the experimental runs performed in a Berty well-mixed reactor. Those equations were derived under very special conditions where the methanol decomposition term could be neglected. It was also observed that in the kinetic equations a term involving the fugacity of CO₂ was required to predict the rate properly. The catalyst deactivation was also taken into account in the analysis.     

Kinetic study of formation of bisphenol a

The condensation reaction of phenol with acetone in an acidic medium to produce bisphenol A has been studied with and without the use of promoters. The promoters used were thioglycollic acid, ethyl mercaptan, butyl mercaptan and hexyl mercaptan. The kinetic study of the reaction shows a first order dependence of the reaction rate individually on phenol and on acetone. The mercaptans greatly enhance the reaction rate whereas thioglycollic acid appears to be only a moderate promoter. The rate-controlling step of the reaction has been found to be the formation of the intermediate carbinol, 2-(4-hydroxyphenyl)-propan-2-ol.