缓冲溶液对TEMPO/NaClO/NaBr选择性氧化纤维素的影响

TEMPO/NaClO/NaBr氧化体系被广泛应用于选择性氧化糖类C6位伯醇羟基,使其成为羧酸盐物质,从而获得更好的水溶性或其他特定功能。但在氧化反应过程中,pH随反应的进行下降,并且存在pH值持续控制繁琐等问题。实验比较分析TEMPO/NaClO/NaBr氧化纤维素在碳酸钠―碳酸氢钠缓冲溶液、硼砂―氢氧化钠缓冲溶液中的适用性,并以滴加的方式向体系中加入氧化剂NaClO溶液,探索两种缓冲体系中各自适宜的NaClO滴加速度。实验结果表明,碳酸钠―碳酸氢钠缓冲溶液和硼砂―氢氧化钠缓冲溶液都适用于TEMPO/NaClO/NaBr氧化体系。与传统方法相比,氧化纤维素的羧基含量可以提高20%～25%。使用缓冲溶液较单一氢氧化钠溶液对稳定pH值有更好的效果,并且方法简便。另外,硼砂―氢氧化钠缓冲溶液对NaClO滴加速度敏感,控制滴加速度可以有效地提高反应活性。     

氧化甲壳素的合成

在TEMPO（2，2，6，6-四甲基哌啶氮氧自由基）和NaBr的催化作用下用NaClO溶液氧化甲壳素得到氧化甲壳素；产品纯化后，经^13C-NMR和红外分析鉴定出糖基C6位羧基的存在；同时对原料的选择和反应的工艺备件作了初步的探索，得到了合适的反应温度（0-5℃）和pH值（10-11），产率迭到45％左右。     

NaOH/硫脲/尿素预处理对棉纤维TEMPO选择性氧化的影响

采用NaOH/硫脲/尿素体系对棉纤维进行预处理,再进行选择性氧化,可以有效提高氧化棉纤维的羧基生成量。对比研究预处理棉纤维与普通棉纤维经2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)选择性氧化后的羧基含量、纤维形态以及黏度。结果表明,经NaOH/硫脲/尿素体系预处理能够加快氧化反应速率,增加羧基生成量,但对纤维有一定的损伤。其中,羧基生成量随着纤维质量分数的增加呈先增加后减少的趋势,当纤维素质量分数为6%时,羧基生成量最大,棉纤维的可及度和反应性提高。纤维形态分析表明,经NaOH/硫脲/尿素体系预处理的棉纤维润胀溶解程度要大于未预处理的氧化棉纤维;在TEMPO的氧化条件下,氧化棉纤维的相对黏度随着纤维素质量分数增加而增加;当纤维素质量分数较高时,氧化过程中氧化棉纤维的羧基生成量和降解程度都近似于原纤维。     

超声协同TEMPO氧化制备阔叶木氧化纳米纤维素

采用超声协同的TEMPO/NaBr/NaClO催化氧化体系制备阔叶木氧化纳米纤维素,探究氧化过程中,随氧化程度增大,纤维素的形貌、尺寸、羧基含量、Zeta电位、得率的变化规律。结果表明,超声作用显著提高了氧化反应速率及羧基含量,且粒径明显低于TEMPO氧化。借助SEM扫描电镜可以看出,超声波的空化作用可以破坏阔叶木纤维的层状结构,提高了纤维的比表面积,对TEMPO氧化起到了促进作用。     

TEMPO氧化纳米纤维素的制备及其对纸张性能的影响

以漂白桉木浆和废报纸为原料,利用2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)/NaBr/NaClO氧化体系对其进行处理制备氧化纳米纤维素,并探究两种氧化纳米纤维素添加量对纸张性能的影响。研究结果表明:桉木浆氧化纳米纤维素的平均纤维长度约为75~95 nm,长径比约为6.5~8.5,均高于废报纸氧化纳米纤维素(45~75 nm,4~6)。添加桉木浆氧化纳米纤维素和废报纸氧化纳米纤维素均可使纸张抗张指数、耐破指数和撕裂指数增加。添加6%桉木浆氧化纳米纤维素时,纸张抗张指数由21.16(N·m)/g增加至31.37(N·m)/g,耐破指数由1.32(kPa·m^(2))/g增加至1.84(kPa·m^(2))/g,撕裂指数由6.61(mN·m^(2))/g增加至8.03(mN·m^(2))/g;添加6%废报纸氧化纳米纤维素时,纸张抗张指数由21.16(N·m)/g增加至27.22(N·m)/g,耐破指数由1.32(kPa·m^(2))/g增加至1.79(kPa·m^(2))/g,添加4%废报纸氧化纳米纤维素,纸张撕裂指数由6.61(mN·m^(2))/g增加至8.12(mN·m^(2))/g,可见,添加桉木浆氧化纳米纤维素效果更佳。添加1%阳离子淀粉,有助于两种氧化纳米纤维素对纸张强度的提高,其中桉木浆氧化纳米纤维素可使抗张指数最大提高51.09%,耐破指数提高50.00%,撕裂指数提高27.62%。     

2,2,6,6-四甲基哌啶氮氧自由基的合成

用自制的2，2，6，6-四甲基哌啶采用廉价的二价金属盐—过氧化氢体系，2，2，6，6-四甲基哌啶氮氧自由基；同时对合成的工艺条件作了初步的探索，得到了产率达到80．17％左右的工艺条件，反应温度65℃、滴加时间6h，30％双氧水与2，2，6，6-四甲基哌啶的物质的量比为2．5。     

纳米纤维素增强天然高分子材料的研究进展

总结了纳米纤维素晶体和纳米纤维素纤丝作为增强材料在天然高分子材料中的最新发展和应用。对比了生物质基纳米纤维素的原料来源、制备方法和形貌尺寸,总结2种纳米纤维素的性能特点,分类探讨了2种纳米纤维素对天然高分子材料的机械性能、阻隔性能、吸水性能和热稳定性的增强效果。纳米纤维素具有纳米尺度、高结晶性和形成氢键的能力,与基体高分子形成强大的氢键网络结构,可以显著提高基体材料的相关性能。纳米纤维素增强天然高分子材料在着重强调机械性能和阻隔性能的包装材料行业具有巨大发展潜力。     

无碱条件下氧气催化氧化2-乙基己醇合成2-乙基己酸

以2-乙基己醇作为原料,O_2作为氧化剂,无碱参与下催化氧化合成2-乙基己酸。使用气相色谱(GC)进行定量分析,气质联用仪(GC-MS)进行定性分析。考察了催化剂、溶剂、反应温度、时间及氧压力对反应的影响。结果表明:2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)/硝酸铜为合适的催化剂体系,乙酸乙酯为合适的溶剂。适宜的反应条件是:催化剂TEMPO用量为2-乙基己醇物质的量的5%、硝酸铜用量为2-乙基己醇物质的量的4%,100℃、0.5 MPa O_2压力下反应6 h,2-乙基己酸收率可达77.1%。O_2恒压条件下该反应是拟一级反应,反应活化能为59.9 k J/mol。主要副产物是3-庚醇和3-庚酮。     

纳米晶体纤维素Ⅱ的制备与表征研究

用硫酸水解棉短绒得到的纳米晶体纤维素Ⅰ(NCC-Ⅰ),经1%的NaOH处理后就可得到纳米晶体纤维素Ⅱ(NCC-Ⅱ)。用X-射线衍射仪、TEM、AFM、FITR和GPC表征,证明NCC-Ⅰ有低的分子量、窄的分子量分布及较高的化学活性;在FTIR谱中,NCC-Ⅰ的羟基波数较之棉短绒的羟基波数有明显的蓝移现象。研究证明纳米晶体纤维素具有十分明显的纳米效应。     

纳米纤维素的制备及应用研究进展

纳米纤维素作为一种绿色无污染的生物质材料,具有高模量、高比表面积、特殊的光学性质、生物相容性好等众多优点,纳米纤维素及其复合材料的广泛应用越来越引起国内外专家的关注,研究其制备途径和应用价值将对未来化工等行业的发展产生巨大影响.本文综述了纳米纤维素的制备途径、改性方法及其在不同领域的应用研究现状,为其研究发展提供一定的...     

2,2,6,6-四甲基哌啶-1-氧自由基在醇氧化研究中的应用

2,2,6,6-四甲基哌啶-1-氧自由基（TEMPO）作为有机小分子,形成的催化醇氧化反应体系相对传统醇氧化具有高效性、高选择性、反应条件温和等优点,可以解决传统醇氧化工艺中反应条件苛刻、成本高以及产生大量污染物的问题,是目前最具前景的醇氧化技术之一。本文综述了近年来关于TEMPO体系在催化醇氧化方面的相关研究进展,重点介绍了均相环境下过渡金属（铜、铁、钌等）参与和无过渡金属参与的TEMPO催化醇氧化,以及多相环境下的固载型TEMPO催化醇氧化,并根据催化反应效率、氧化成本、实际应用性等因素比较总结了均相催化和非均相催化两种类型催化氧化体系的优缺点。指出离子液体与TEMPO的耦合体系、廉价过渡金属掺杂的TEMPO体系和高稳定性碳基材料负载型TEMPO体系是该类型催化剂优化调控的目标与方向。     

Oxidation of Amino Diols Mediated by Homogeneous and Heterogeneous TEMPO

The conversion of amino diols to aminohydroxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6‐tetramethylpiperidine 1‐oxyl radical) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homogeneous phase or entrapped in a sol‐gel matrix, as catalytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic‐inorganic silica sol‐gel catalysts are more selective mediators for the oxidation of benzylic amino diols like the potent antibiotic chloramphenicol which, under homogeneous conditions, are unselectively oxidized to benzoic acids.     

One‐Pot Homogeneous and Heterogeneous Oxidation of Glycerol to Ketomalonic Acid Mediated by TEMPO

Glycerol, an increasingly abundant by‐product of biodiesel production, is selectively converted to ketomalonic acid in one pot at pH 10 using NaOCl as regenerating oxidant in water at 2 °C in the presence of catalytic Br⁻ along with the radical TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl). The reaction can also be conducted at completion over a sol‐gel silica glass doped with the nitroxyl radical. Considering the stability and versatility of such doped glasses, these materials show real promise as reusable metal‐free catalysts for the conversion of a readily available and renewable biofeedstock into a highly valued compound.     

Laccase/2,2,6,6‐Tetramethylpiperidinoxyl Radical (TEMPO): An Efficient Catalytic System for Selective Oxidations of Primary Hydroxy and Amino Groups in Aqueous and Biphasic Media

Copper salts/2,2,6,6‐tetramethylpiperidinoxyl radical (TEMPO) catalytic systems enable efficient aerobic oxidations of primary alcohols but they generally show a reduced reactivity in aqueous medium. Herein, we report an oxidative catalytic system composed of Trametes versicolor laccase and TEMPO, which is able to work in buffer solutions at room temperature using ambient air. Although this catalytic system displays great efficiency in aqueous systems, the addition of methyl tert‐butyl ether allows the reduction of TEMPO loading, also enhancing the solubility of hydrophobic compounds. This practical methodology promotes the chemoselective aerobic oxidation of hydroxy or amino groups, leading to interesting organic derivatives such as aldehydes, lactones, hemiaminals or lactams.

     

Polyurethane‐ and Polystyrene‐Supported 2,2,6,6‐Tetramethyl‐ piperidine‐1‐oxyl (TEMPO); Facile Preparation,Catalytic Oxidation and Application in a Membrane Reactor

In this contribution, the facile synthesis of two new polymer‐supported 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) catalysts and their application in the catalytic oxidation of alcohols to carbonyl compounds are described. For attachment of the TEMPO group to the polymer an isocyanate functionalized polymer is chosen. This new approach facilitates the synthesis in comparison with previously existing methods which generally require deprotonation of TEMPO prior to reaction with the polymer. Following this approach, polyurethane (PU)‐ and polystyrene (PS)‐based TEMPO catalysts are prepared in a one‐step reaction from commercially available compounds. Both polymer‐supported catalysts showed promising yields for a variety of substrates using inorganic and/or organic co‐oxidants in biphasic and/or monophasic systems. The recyclability of the corresponding catalysts was studied in repetitive batch experiments using filtration or distillation depending on the support type. Furthermore, application of the homogeneous polyurethane‐supported TEMPO for the selective oxidation of benzyl alcohol in a continously operated membrane reactor is demonstrated.     

Porous Silica Beads Supported TEMPO and Adsorbed NOx (PSB‐TEMPO/NOx): An Efficient Heterogeneous Catalytic System for the Oxidation of Alcohols under Mild Conditions

The combination of NO_x gas which is stored in the pore canals of porous silica beads (PSB) with a heterogeneous catalyst, PSB‐supported 2,2,6,6‐tetramethylpiperdine 1‐oxyl (PSB‐TEMPO, 1 ), afforded a highly efficient, widely applicable, and efficiently recyclable approach for the selective aerobic oxidation of alcohols. This novel catalytic system (PSB‐TEMPO/NO_x) can be employed in the oxidation of a wide range of alcohols to their corresponding aldehydes and ketones with selectivities as high as 99% at complete conversions under mild conditions. O₂ is the terminal oxidant. PSB‐TEMPO can be recycled for more than 10 times without significant loss of activity.     

TEMPO and Carboxylic Acid Functionalized Imidazolium Salts/Sodium Nitrite: An Efficient,Reusable, Transition Metal‐Free Catalytic System for Aerobic Oxidation of Alcohols

An effective catalytic system comprising a 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) functionalized imidazolium salt ([Imim‐TEMPO]⁺ X⁻), a carboxylic acid substituted imidazolium salt ([Imim‐COOH]⁺ X⁻), and sodium nitrite (NaNO₂) was developed for the aerobic oxidation of aliphatic, allylic, heterocyclic and benzylic alcohols to the respective carbonyl compounds with excellent selectivity up to >99%, even at ambient conditions. Notably, the catalyst system could preferentially oxidize a primary alcohol to the aldehyde rather than a secondary alcohol to the ketone. Moreover, the reaction rate is greatly enhanced when a proper amount of water is present. And a high turnover number (TON 5000) is achieved in the present transition metal‐free aerobic catalytic system. Additionally, the functionalized imidazolium salts are successfully reused at least four times. This process thus represents a greener pathway for the aerobic oxidation of alcohols into carbonyl compounds by using the present task‐specific ionic liquids in place of the toxic and volatile additive, such as hydrogen bromide, bromine, or hydrogen chloride (HBr, Br₂ or HCl), which is commonly required for the transition metal‐free aerobic oxidation of alcohols.     

基于FPGA的闭环自动增益控制系统

设计了一种基于FPGA的闭环自动增益控制系统,采样保持部分利用互锁技术采集VCA810输出的第1个有效波峰值电压大小,再经FPGA的AGC控制算法,产生控制电压值,经电压调整后,控制VCA810的输出.对本设计过程中产生的小数,做了变小数为整数的处理,从而提高了精度.     

Aerobic Oxidation of Benzylic Alcohols in Water by 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)/Copper(II) 2‐N‐Arylpyrrolecarbaldimino Complexes

Novel copper(II) 2‐N‐arylpyrrolecarbaldimine‐based catalysts for the aerobic oxidation of benzylic alcohols mediated by the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radical are reported. The catalytic activity for both synthesized and in situ made complexes in alkaline water solutions was studied revealing high efficiency and selectivity (according to GC selectivity always >99%) for both of these catalytic systems. For example, quantitative conversion of benzyl alcohol to benzaldehyde can be achieved with the in situ prepared bis[2‐N‐(4‐fluorophenyl)‐pyrrolylcarbaldimide]copper(II) catalysts in 2 h with atmospheric pressure of O₂ at 80 °C. Interestingly, these catalysts can utilize dioxygen as well as air or hydrogen peroxide as the end oxidants, producing water as the only by‐product.     

城市污水处理A/A/O工艺中溶解氧的自动控制优化设计

为了解决A/A/O工艺污水处理系统在进水负荷波动较大时曝气池中溶解氧(DO)的波动范围大的问题,该文以某A/A/O工艺的污水处理厂作为试运行系统,进行DO的自动控制优化研究,在传统的DO控制方法上加入曝气池的模型算法来进行DO控制的优化设计.试运行系统运行表明该控制方法可以使DO的控制精度范围达到±0.2mg/L.