Kinetics of lipid oxidation in the presence of cinnamic acid derivatives

The effects of seven (prenyl‐ and methoxy‐) derivatives of cinnamic acid (0.1 mM) on the kinetics of lipid (sunflower oil triacylglycerols, TGSO) bulk phase oxidation at 80 °C have been compared. Synthesis of prenyl cinnamic acid derivatives: 3‐prenyl‐4‐hydroxy‐cinnamic acid (PHC), 3,5‐diprenyl‐4‐hydroxy‐cinnamic acid (DPHC), 2,2‐di‐methyl‐6‐carboxy‐ethenyl‐2H‐benzopyran (DMCB), 2,2‐dimethyl‐6‐carboxy‐ethenyl‐8‐prenyl‐2H‐benzopyran (DCEPB) present in Brazilian propolis has been performed. The monoprenyl derivative (PHC) has been found to exert a higher antioxidant activity as compared to the diprenyl derivative (DPHC). However, cinnamic acid derivatives DMCB and DCEPB have caused no change in the kinetics of TGSO oxidation. The results obtained have been compared with those on related compounds containing a cinnamic acid moiety as a structural feature, such as 4‐hydroxy‐cinnamic (p‐coumaric), 3‐methoxy‐4‐hydroxy‐cinnamic (ferulic) and 3,5‐dimethoxy‐4‐hydroxy‐cinnamic (sinapic) acids, as well as with data on butylated hydroxytoluene (BHT) and α‐tocopherol (αToc). PHC has shown a stronger antioxidant efficiency than BHT, p‐coumaric and ferulic acid, but a weaker antioxidant efficiency than α‐Toc and sinapic acid. The observed antioxidant effect of DPHC was stronger than that of p‐coumaric and ferulic acids and weaker than that of α‐Toc, BHT and sinapic acid.     

十二烷基硫酸钠对膜蒸馏过程影响

膜蒸馏具有较低的操作压力、操作温度以及运行成本等优点，因此在水处理方面有广泛的应用前景。但是膜蒸馏过程中的膜润湿和膜污染现象仍然是阻碍其工业化应用的主要问题。表面活性剂作为一种能显著降低溶液表面张力、改变进料液性质的物质，对膜蒸馏造成的影响值得被研究。基于此，研究了在直接接触式膜蒸馏（DCMD）过程中表面活性剂对不同商业微孔疏水膜造成的影响，选用了一种常见的阴离子表面活性剂十二烷基硫酸钠(SDS)进行实验。结果表明，进料液中SDS浓度的上升会引起更为严重的膜润湿现象，并且所使用的三种商业膜中，双疏膜抗润湿性最强，而PVDF膜最弱。而当Ca²⁺大量存在于进料液中时，Ca²⁺与SDS的聚集降低了膜润湿的程度但其在膜表面的沉积造成了严重的膜污染。界面相互作用自由能的计算结果表明Ca²⁺/SDS与PVDF膜之间的吸引力最大、PTFE膜其次、双疏膜最小，这一结果与膜蒸馏过程中通量变化情况相符。     

Fenton法处理高浓度硫酸盐的日用化工废水

采用Fenton法对高浓度硫酸盐的LAS废水进行处理,研究Fenton方法对此类废水的最佳处理条件。实验表明,在H2O2的质量浓度为3.0 mg/L,摩尔比n(H2O2)∶n(Fe2+)=8∶1,反应时间为2 h时,废水的COD从9 000 mg/L左右下降到3 000 mg/L左右,出水与生活污水相混合进入生物处理系统,从而可以达到广东省一级排放标准。     

Fenton氧化-好氧接触工艺处理高浓度硫酸盐的LAS废水

采用Fenton氧化-好氧接触工艺替代常规的物化法和生物法对含高浓度硫酸盐的LAS废水进行处理,并研究其影响因素及适宜条件。Fenton试剂氧化的优化操作条件:Fe2 的质量浓度为0.6 g/L,H2O2质量浓度为0.12 g/L,反应40 min,实验结果表明,经Fenton氧化后废水的COD由1 500 mg/L降至230 mg/L,废水的LAS质量浓度由490 mg/L降至23 mg/L。在上述的操作条件下,采用Fenton氧化的方法对某日用化工厂排放的实际废水进行预处理,Fenton氧化后的出水在好氧接触氧化装置中停留20 h,最终出水的COD和LAS均达到广东省一级废水排放标准,COD和LAS的总去除率分别达到95%和99%以上,处理效果良好。     

流动注射分光光度法测定环境水样中的十二烷基硫酸钠

基于孔雀绿与十二烷基硫酸钠(SDS)反应形成稳定的缔合物,建立了测定SDS的流动注射分光光度法。实验表明,SDS在0~2.4 mg/L,质量浓度ρ与缔合物峰高h呈良好的线性关系,线性回归方程为:h(mV)=18.783ρ(mg/L) 1.919 2;对0.5 mg/L SDS标准溶液连续进样9次进行测定,相对标准偏差1.3%,精密度良好,方法的检出限(3σ)为0.006 5 mg/L;应用该法测定环境水样中SDS,回收率97.5%~101%。     

Kinetics of inhibited oxidation of lipids in the presence of 1-octadecanol and 1-palmitoylglycerol

The kinetics of initiated oxidation of sunflower oil methyl esters at 50°C in the presence of the phenolic inhibitorp-methoxyphenol are investigated. It is established that addition of 0.1 M 1-octadecanol and of 0.1 M 1-palmitoylglycerol leads to a 1.5- or 2.3-fold decrease of the rate constant of chain termination on the inhibitor, which proves the blocking of its effect due to the formation of a complex based on a hydrogen bond. The stronger effect of 1-palmitoylglycerol is explained by the presence of two hydroxyl groups in its molecule.     

糖基双子阳离子表面活性剂与十二烷基硫酸钠复配性能研究

测定了糖基双子阳离子表面活性剂(SGCS)与十二烷基硫酸钠(K_(12))复配体系的稳定性和表面性能。由实验结果可知,在宽的复配范围内不同碳链长度的SGCS与K_(12)均有良好的复配稳定性;C_(14)-SGCS/K_(12)复配体系表现出明显的协同增效作用,当n(C_(14)-SGCS)∶n(K_(12))为3∶5时复配溶液临界胶束浓度(cmc)、cmc时的表面张力(γ_(cmc))和降低表面张力的效率(pc_(20))分别为1.1×10~(-5) mol/L、23.69 mN/m和5.48,均明显优于C_(14)-SGCS和K_(12)自身的表面性能。     

Mechanism of micelle formation in sodium dodecyl sulfate and cetyltrimethylammonium bromide

pH changes as a function of concentration for sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) were observed by addition of 1 N HCl and 1 N KOH. pH values increased up to the critical micellar concentration (CMC) for the SDS/HCl system and decreased for the CTAB/KOH system. In the SDS/HCl and CTAB/KOH systems, the micellar phase had a fixed composition and was homogeneous and monodisperse above the CMC. However, in the SDS/KOH and CTAB/HCl systems, pH values increased continuously and gradually below and above the CMC, and the properties of the micellar phase changed as a function of concentration, giving rise to inhomogeneity and polydispersity.     

Vibrational spectroscopic study of distribution of sodium dodecyl sulfate in latex films

The migration of the surfactant sodium dodecyl sulfate (SDS) to the film-air (F-A) and film-substrate (F-S) interfaces during coalescence of a latex of methyl methacrylate and ethyl acrylate functionalized with methacrylic acid was monitored by IR and ATR-FTIR spectroscopic techniques. Both F-A and F-S interfaces showed surfactant enrichment, revealing a nearly parabolic distribution of surfactant throughout the film.     

Kinetics of precipitation of surfactants. II. Anionic surfactant mixtures

Precipitation kinetics were measured for calcium-induced precipitation of mixtures of two anionic surfactants. The overall time required for precipitation to occur increased dramatically in specific ranges of compositions for the surfactant mixtures when compared to single components. Adsorption of the nonprecipitating surfactant onto the precipitate surface was shown to be responsible for this remarkable synergism. The higher the supersaturation of surfactant monomers, the more rapidly precipitation occurred. Under conditions where both surfactants were supersaturated, precipitation sometimes occurred in stepwise fashion, where crystals of different composition were formed with different induction times. Image analysis of the crystalline precipitate showed that crystal habit was affected when the two surfactants were mixed, indicating that processes such as adsorption and coprecipitation (most likely by inclusion) were occurring. When the crystals were allowed to age in solution for a period of 1 wk, the crystalline phase from the mixed surfactant solutions was found to separate into two types of crystals, which resembled week-old crystals formed from single surfactant systems.     

Effect of sodium dodecyl sulfate on shape-memory properties of side-chain crystalline hydrogel via micellar copolymerization

A chemical shape-memory hydrogel containing crystalline structure is prepared via micellar copolymerization of hydrophilic monomer acrylamide (AM) and hydrophobic monomer octadecyl acrylate (C18) in a sodium dodecyl sulfate (SDS) solution. The influence of SDS on the shape-memory behavior of hydrogel investigated by differential scanning calorimetry (DSC) and Temperature-dependent X-ray indicate that the melting and crystallization peaks derived from the thermal properties of C18 units is different from peaks corresponding to the pure SDS. In addition, the microstructure evolution information of hydrogels dose not change upon heating process, regardless of the presence or absence of SDS. Therefore, only the hydrophobic associations formed by C18 blocks play a decisive role in the shape memory function of hydrogel system. The difference between the transition process (from temporary shape to permanent shape) of hydrogel with and without SDS at different temperature is because that the hydrophobic region of side chain crystallization of SDS-free hydrogel may escape the restriction of SDS and become more sensitive to temperature, they can preferentially return to their initial shape under the same time and temperature than SDS-containing gels. Whether SDS exists only affect the speed of shape memory behavior, but not the microstructure evolution of hydrogel system.     

模拟过氧化物酶催化苯酚氧化降解的动力学

为了研究模拟过氧化物酶催化降解苯酚的机理,一种大环金属配合物CuL(配体L:高氯酸-5,7,7,12,14,14-六甲基-1,4,8,11-四氮杂环-4,11-二烯)作为模拟过氧化物酶用于催化过氧化氢氧化苯酚的降解。用高效液相色谱法和分光光度法分析了苯酚催化氧化的主要产物和反应速率。根据实验结果提出了该催化反应的反应机理,并建立了相关的动力学模型。研究表明,大环铜金属配合物表现出过氧化物酶的催化作用特征。因此,所用大环铜配合物作为模拟过氧化物酶在催化苯酚氧化过程中是一种有效的催化剂。     

对二甲苯液相氧化过程中燃烧副反应动力学

During the liquid-phase oxidation of p-xylene, over-oxidation of reactant, intermediates and solvent to carbon dioxide and carbon monoxide is generally known as the burning side reaction. Batch and semi-continuous experiments were carried out, and the experimental data of the burning side reaction were analyzed and reported in this paper. The results showed that the rates of burning side reactions were proportional to the rates of the main re-action, but decreased with the increasing concentrations of reactant and intermediates. The inter-stimulative and competitive relationship between the burning side reaction and the main reaction was confirmed, and the rates of the burning side reaction could be described with some key indexes of the main reaction. According to the mecha-nism of the side reactions and the kinetics model of main reaction which were proposed and tested in the previous papers, a kinetic model of the burning side reactions involving some key indexes of the main reaction was devel-oped, and the parameters were determined by data fitting of the COx rate curves. The obtained kinetic model could describe the burning side reactions adequately.     

Poly(o-aminophenol) film prepared in the presence of sodium dodecyl sulfate: Application for nickel ion dispersion and the electrocatalytic oxidation of methanol and ethylene glycol

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode. The electrochemical behavior of the SDS-POAP carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M HClO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode. A good redox behavior of the Ni(III)/Ni(II) couple at the surface of electrode can be observed. The electrocatalytic oxidations of methanol and ethylene glycol (EG) at the surface of the Ni/SDS-POAP electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and POAP-modified carbon paste electrodes, the SDS-POAP electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation. Finally, using a chronoamperometric method, the catalytic rate constants (k) for methanol and ethylene glycol were found to be 2.04 × 10⁵ and 1.05 × 10⁷ cm³ mol⁻¹ s⁻¹, respectively.     

Kinetics of hydrogen reduction of sodium sulfate mixed with sodium titanate

The hydrogen reduction kinetics of solid sodium sulfate mixed with sodium titanate are studied in a thermogravimetric system. The conversion-time curves of the hydrogen reduction are sigmoidal in shape and are well described by the nucleation and growth model up to about 60% conversion. The reduction rate of this mixture is much faster than that of pure sodium sulfate. In the deceleratory conversion period, the reduction is controlled by gas diffusion through a product layer. Activation energies of 302 and 179 kJ/mol are obtained, respectively, for the nucleation and growth, and diffusion limited period. The influence of hydrogen concentration, steam concentration, sodium sulfate fraction, and sodium sulfide addition is also studied. A reaction mechanism is proposed for the hydrogen reduction in the solid state.     

Investigation of factors influencing sodium sulfide oxidation in the presence of polymeric heterogeneous catalysts of transition metal oxides

The activity of heterogeneous catalysts of transition metal oxides and their mixtures deposited on the polymeric matrix in the oxidation of sodium sulfide was investigated. It is shown that mixtures of manganese oxide and other transition metal oxides have high catalytic activity. It was evident that the positive synergistic effect occurred in the combined action of two or more catalytically active transition metal oxides, and the maximum effect was observed in the mixture of three catalytic agents of transition metal oxides. Catalytic mechanism of transition metal oxides for sulfide oxidation was studied. The kinetics of formation of products of sodium sulfide oxidation was studied in the presence of heterogeneous catalysts based on phthalocyanine cobalt and transition metal oxides. The dependence of the rate of formation of products of sodium sulfide oxidation on alkali concentration was investigated. Some factors influencing the oxidation rate such as sulfide, oxygen and alkaline concentrations, antioxidant and oxidation products were investigated.     

十二烷基硫酸钠/正丁醇/正庚烷/水微乳液性质研究

25℃时,绘制十二烷基硫酸钠(SDS)/正丁醇/正庚烷/水体系在不同R值(水和SDS的摩尔比)时的相图,得出该体系能形成W/O微乳液的配比为:正丁醇的质量分数在25%~60%,正庚烷的质量分数在0~80%。该体系在室温下能够形成较大范围的W/O单相微乳液区,R值对微乳区的面积和所在的位置无太大的影响。采用电导率曲线讨论了加水稀释过程中,体系由W/O型→双连续型→棒状液晶→层状液晶→双连续型→O/W型的微观结构转变。采用稀释法求得其W/O型微乳液体系的结构参数,结果表明:体系的水内核半径Rw在讨论的范围内随VH2O、R值的增加而增大。含水量增加,自由能-ΔGcO→i降低,对微乳液体系的稳定不利;含水量越低,越有利于微乳液的形成和稳定。     

Interaction of main‐chain polycations with sodium dodecyl sulfate

The interaction of the main‐chain polycations 2,2‐ionene (I_2,2) and 3,3‐ionene (I_3,3) with sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. It was confirmed that the interaction is cooperative and a stoichiometric 1:1 complex of I_2,2–SDS or I_3,3–SDS with regular structure forms as a precipitate irrespective of the molar ratio of the components. It is completely different from the interaction of side‐chain polycations such as the poly[(vinyl pyridine)‐co‐styrene] copolymer cation (PVSC) with SDS, in which no cooperative effect was observed. The driving force responsible for the cooperative effect is believed to be the hydrophobic attraction between the SDS molecule already linked on the ionene chain and the next SDS molecule to be entered. It was also confirmed that the structures of the complexes are very different, ie the ionene–SDS complexes exhibit high regularity whereas the PVSC–SDS complex is irregular. © 2001 Society of Chemical Industry     

The effect of micellar lifetime on the rate of solubilization and detergency in sodium dodecyl sulfate solutions

The slow relaxation time (τ₂) of sodium dodecyl sulfate (SDS) micelles, measured by the pressure-jump technique, was maximum at 200 mM concentration at 25°C, indicating that the most stable micelles are formed at this concentration. This is presumably related to the optimum molecular packing in the micelle. The rate of solubilization of benzene and Orange OT dye into SDS solutions was also maximum at 200 mM concentration. The results are explained as follows: The distance between micelles (i.e., intermicellar distance) decreases as the surfactant concentration (or the number of micelles) increases, resulting in a stronger electric repulsion between micelles. Therefore, the micelles become more rigid, due to the compressive force of intermicellar repulsion, as the concentration increases up to 200 mM SDS. With further increase in the SDS concentration, the micellar shape changes from spherical to cylindrical to accommodate more surfactant molecules in the solution and to minimize the free energy of the system. The interior of the tightly packed micelles is more hydrophobic than that of loosely packed micelles and, therefore, the tightly packed micelles induce rapid solubilization of nonpolar molecules (e.g., benzene, Orange OT) into these micelles.