亚临界水/二氧化碳中纤维素降解制备5-羟甲基糠醛的机理及动力学

采用气相色谱-质谱联用对亚临界水/二氧化碳二元体系中纤维素降解制备5-羟甲基糠醛(5-HMF)的反应产物进行分析,考察了纤维素降解生成5-HMF的机理,建立了纤维素降解反应的动力学方程.实验得出,在亚临界水体系以亚临界水/二氧化碳二元体系中纤维素降解生成5-羟甲基糠醛的反应均为一级反应,纤维素降解的表观活化能分别为113.32 kJ/mol和104.74 kJ/mol.     

超声波辅助酶法提取蓝莓果渣花色苷的工艺优化及降解动力学

摘要：以蓝莓果渣为原料，在单因素实验的基础上通过响应面优化得到超声波辅助酶法提取花色苷的最佳工艺，并通过构建降解动力学模型考察不同光照时间和温度对花色苷稳定性的影响。结果表明：超声波辅助酶法提取蓝莓花色苷工艺的最佳参数为：乙醇体积分数60%、液料比40:1（mL/g）、酶解时间80 min，花色苷得率为10.571±0.080 mg/g。花色苷在不同光照时间和温度下的降解模型均符合零级动力学方程。紫外光、日光灯、避光条件对花色苷稳定性影响程度依次减弱，4℃下保存花色苷其损失量仅为5.5%；在40~80℃范围内，花色苷的热降解速率随着温度的升高而增加，半衰期随着温度的升高而降低，温度系数Q10随温度的升高而增大，活化能Ea为46.6729 kJ/mol。此外，由热力学参数可知花色苷热降解为非自发反应。研究结果可为蓝莓资源的有效利用及其应用潜力和价值的提升提供参考。     

有机酸对甜高粱渣亚临界水解产物的影响

半纤维素的高效转化是提高甜高粱渣原料全组分利用的关键技术之一。采用亚临界水热预处理方法,并将强度因子R0引入研究过程,考察了不同温度(160~200℃)和反应时间(10~60 min)对甜高粱渣水解反应的影响。在这基础上,进一步考察了多种有机酸(乳酸、醋酸及乳酸+醋酸)对亚临界水解效果的影响。实验表明,当强度因子lg R0=3.96(180℃,40 min)时,采用不外加酸的亚临界水热预处理工艺得到的最大木糖浓度为4.79 g·L~(-1);有机酸的加入可强化水解反应,提高木糖浓度;与单一乳酸或醋酸处理方法相比,加入同浓度的乳酸+醋酸既可以促进半纤维素水解,又可以抑制副产物生成;在温度180℃,时间40 min,乳酸+醋酸(乳酸:醋酸=6:4)的浓度1%(质量)的条件下,木糖浓度为7.92 g·L~(-1)。     

有机酸对甜高粱渣亚临界水解产物的影响

半纤维素的高效转化是提高甜高粱渣原料全组分利用的关键技术之一。采用亚临界水热预处理方法,并将强度因子R₀引入研究过程,考察了不同温度（160~200℃）和反应时间（10~60 min）对甜高粱渣水解反应的影响。在这基础上,进一步考察了多种有机酸（乳酸、醋酸及乳酸+醋酸）对亚临界水解效果的影响。实验表明,当强度因子lgR₀=3.96（180℃,40 min）时,采用不外加酸的亚临界水热预处理工艺得到的最大木糖浓度为4.79 g·L^-1;有机酸的加入可强化水解反应,提高木糖浓度;与单一乳酸或醋酸处理方法相比,加入同浓度的乳酸+醋酸既可以促进半纤维素水解,又可以抑制副产物生成;在温度180℃,时间40 min,乳酸+醋酸（乳酸：醋酸=6：4）的浓度1%（质量）的条件下,木糖浓度为7.92 g·L^-1。     

超声强化亚临界水萃取脱脂葡萄籽中原花青素的动力学研究

根据质量衡算微分模型和运用Fick第一定律,建立了超声强化亚临界水萃取(USWE)和亚临界水萃取(SWE)原花青素的动力学模型,并通过对比这2个模型说明了超声对亚临界水萃取的强化作用。结果表明,Y=5.3974×(1-e~(-0.001 4t))和Y=5.2019×(1-e~(-0.001 2t))分别是USWE和SWE原花青素的动力学模型,并且这2个动力学模型都能很好地模拟萃取的过程;对比这2个模型方程的参数可知,超声能够加快葡萄籽内部原花青素的扩散及促进其解吸,因此能够对SWE起到强化作用。     

亚临界水萃取植物精油的模型

Mechanisms that control the extraction rate of essential oil from Zataria multiflora Boiss. (Z. multiflora) with subcritical water (SW) were studied. The extraction curves at different solvent flow rates were used to determine whether the extractions were limited primarily by the near equilibrium partitioning of the analyte between the matrix and solvent (i.e. partitioning thermodynamics) or by the rates of analyte desorption from the matrix (i.e. ki-netics). Four simple models have been applied to describe the extraction profiles obtained with SW: (1) a model based solely on the thermodynamic distribution coefficient KD, which assumes that analyte desorption from the ma-trix is rapid compared to elution; (2) one-site kinetic model, which assumes that the extraction rate is limited by the analyte desorption rate from the matrix, and is not limited by the thermodynamic (KD) partitioning that occurs dur-ing elution; (3) two-site kinetic model and (4) external mass transfer resistance model. For SW extraction, the thermodynamic elution of analytes from the matrix was the prevailing mechanism as evidenced by the fact that ex-traction rates increased proportionally with the SW flow rate. This was also confirmed by the fact that simple re-moval calculations based on determined KD (for major essential oil compounds) gave good fits to experimental data for flow rates from 1 to 4 ml•min－1. The results suggested that the overall extraction mechanism was influenced by solute partitioning equilibrium with external mass transfer through liquid film.     

亚临界水中的超声空化泡动力学研究

为探究超声空化泡在亚临界水中的动力学行为,本文基于流体控制方程和多相流模型,使用计算流体力学仿真软件对亚临界水中的超声空化泡进行建模与数值仿真,研究了空化泡从在运动过程中的形态变化,以及流体区域内速度,压力的分布变化,并对影响空化泡动力学行为的因素进行探究.结果表明,在同等条件下,常温水中的空化效果比亚临界水中的空化效...     

亚临界水对钢渣再生脱硫的作用

在亚临界条件下进行了钢渣再生脱硫反应,结果表明,钢渣脱硫反应为流体和固体相间进行的多相反应,亚临界条件可大大提高反应速度和反应率.上述多相反应的阻力来自于传质阻力和界面化学反应阻力,主要阻力形式取决于反应温度,当温度超过473 K,由界面化学反应阻力转变为传质阻力.在373～473 K温度范围,脱硫率随温度变化很大,由小于10%增加到45%.在高温区,改善反应动力学条件成为提高钢渣再生脱硫率的关键.亚临界水过处理会使CaO过氧化,造成一定的回硫.     

银杏内酯的亚临界水提取工艺研究

为了提高银杏内酯的提取率及提取效率,采用亚临界水提取银杏叶中银杏内酯,通过单因素实验探讨了提取温度、提取时间、提取次数和料液比对银杏叶中银杏内酯提取率的影响。运用正交实验优化提取工艺条件如下:提取温度180℃,提取时间30min,提取3次,料液比1∶25(g∶mL),在此条件下,银杏内酯提取率为0.4623%。亚临界水提取银杏内酯具有绿色环保、无有机溶剂残留、提取率高等特点。     

人工神经网络建立超声耦合亚临界水提取数学模型

采用超声耦合亚临界水提取香菇多糖,用人工神经网络技术建立提取数学模型,以提取温度、提取时间、提取压力、料液比、超声功率作为网络输入,香菇多糖得率作为输出,首先对亚临界水提取和超声耦合亚临界水提取单因素条件下的香菇多糖得率进行模拟预测,然后利用Design-expert软件对影响因素进行优化实验,分别用响应曲面法和人工神经网络进行多糖得率的模拟预测对比,并对最优化条件进行实验验证。结果表明,人工神经网络拟合值与实验值能很好的吻合,其拟合效果在一定程度上优于响应曲面。     

Thermal Degradation Kinetics of Carotenoids in Palm Oil

In the present work, a detailed study is performed for carotene thermal degradation in palm oil at four temperatures ranging from 170 to 230 °C. The heating process was carried out with injection of nitrogen, and the samples were collected every 20 min during a total heating period of 140 min. HPLC analysis was conducted to monitor the carotenoids and tocols variations over the heating time at each temperature. The experimental data were then compared to literature data concerning carotenoids thermal degradation. The thermal degradation kinetics of carotenoids in palm oil followed an order superior to 1. The dependence of constant rates with temperature obeyed the Arrhenius relationship. The activation energy for the carotenoids thermal degradation in palm oil was found to be 109.4 kJ/mol.     

Kinetics of Palm Oil Methanolysis

A kinetics study of palm oil methanolysis was conducted at three different temperatures and three different concentrations of catalyst, sodium hydroxide, keeping constant the molar ratio of methanol to oil and the rotational speed of the impeller (6:1 and 400 rpm). The maximum conversion of palm oil and productivity to methyl esters were obtained at 60 °C and 1 wt% of NaOH based on palm oil, and they were 100 and 97.6%, respectively. The statistical analysis of conversions of palm oil and productivities to methyl esters as functions of temperature and concentration of catalyst, after 80 min of reaction, allowed them to fit second order polynomial equations, which adequately describe the experimental behavior. The experimental data appear to be a good fit into a second order kinetic model for the three stepwise reactions, and the reaction rate constants and the activation energies were determined. In this article we present the kinetic constant and activation energies for the experiments with 0.2% wt of NaOH. The effect of molar ratio on the concentration of products was investigated, while the temperature (55 °C), the concentration of catalyst (0.60 wt% of NaOH), and the rotational speed (400 rpm), were held constant. The results showed that the conversion and the productivity increased due to methanol excess, and were higher for the reactions with a molar ratio of 6:1.     

Graft Copolymerization of Acrylamide onto Oil Palm Empty Fruit Bunch (OPEFB) Fiber

Grafting of acrylamide (AAm) onto oil palm empty fruits bunch fiber using hydrogen peroxide as initiator and methyl acrylate as comonomer was investigated. The amount of comonomer needed to make grafting of acrylamide possible was determined. The percentage of poly(acrylamide) and the comonomer in the final graft copolymer was estimated by elemental analysis. Results obtained indicated that methyl acrylate facilitated the incorporation of acrylamide monomer onto OPEFB. The reactivity ratios for both monomers were determined by using Fineman–Ross plot. The effects of reaction temperature and period as well as amount of the initiator, solvent, monomer and comonomer on the percentage of grafting at fixed amount of comonomer (11 mmol) were studied. Maximum percentage of grafting was achieved when the amount of initiator and solvent 3.98×10⁻³ mol and 50 mL respectively. The optimum reaction temperature was 50 ^○C and the reaction period was 90 min. Highest percentage of grafting was 232% when 25.6 mmol of acrylamide was used under these optimum conditions. The presence of functional group in the grafted polymer is characterized by infrared spectroscopy and the surface morphology is observed by scanning electron microscopy. Thermoanalytic investigation on OPEFB and OPEFB-g-PAAM were carried out to evaluate the thermal stability and respective activation energy of the materials.     

Graft Copolymerization of Methyl Acrylate onto Oil Palm Empty Fruit Bunch (OPEFB) Fiber

Graft copolymerization of methyl acrylate (MA) onto OPEFB fiber has been successfully carried out using hydrogen peroxide and ferrous ammonium sulfate as initiators in an aqueous medium. The effects of reaction temperature, reaction period, and amount of monomer and initiators on the percentage of grafting were investigated. The results show that the percentage of grafting depends on reaction period and temperature as well as concentration of monomers and initiators. With 33.36 mmol of MA, the optimum percentage of grafting was obtained when the reaction was carried out using 6.00 mmol of H₂O₂ and 0.191 mmol of Fe²⁺ for 210 min at 75°C. The presence of the functional group in the grafted polymers was characterized by FTIR spectroscopy. Scanning electron microscopy was used to study the surface morphology. Thermogravimetric analysis indicated that the grafted OPEFB is thermally stable than the OPEFB     

Degradation of Pentoses and Hexouronic Acids in Subcritical Water

The degradation of arabinose, xylose, ribose and lyxose in subcritical water was measured at 200, 220 and 240 °C. Ribose was the most rapidly degraded among the pentoses tested. The degradation of the glucuronic and galacturonic acids proceeded at lower temperatures than that of the pentoses, and was measured at 140, 150 and 160 °C. The degradation processes of the pentoses and hexouronic acids could be expressed by the Weibull model, and the kinetic parameters were then estimated. The activation energy and frequency factor for the degradation of each substrate were estimated from the temperature dependence of the rate constant. The enthalpy‐entropy compensation held for the degradation of the pentoses as well as the hexoses, which suggests that the degradation of the hexouronic acids proceeded through a mechanism different from that for the pentoses and hexoses. The molar yield of a pentose to furfural was ca. 0.3 at any temperature, irrespective of the pentose type. Acidic compounds were also formed from the pentoses in proportion to the amount of consumed substrates. The formation of acidic compounds resulted in a rapid decrease in pH.     

Effect of Fiber Esterification on Fundamental Properties of Oil Palm Empty Fruit Bunch Fiber/Poly(butylene adipate-co-terephthalate) Biocomposites

A new class of biocomposites based on oil palm empty fruit bunch fiber and poly(butylene adipate-co-terephthalate) (PBAT), which is a biodegradable aliphatic aromatic co-polyester, were prepared using melt blending technique. The composites were prepared at various fiber contents of 10, 20, 30, 40 and 50 wt% and characterized. Chemical treatment of oil palm empty fruit bunch (EFB) fiber was successfully done by grafting succinic anhydride (SAH) onto the EFB fiber surface, and the modified fibers were obtained in two levels of grafting (low and high weight percentage gain, WPG) after 5 and 6 h of grafting. The FTIR characterization showed evidence of successful fiber esterification. The results showed that 40 wt% of fiber loading improved the tensile properties of the biocomposite. The effects of EFB fiber chemical treatments and various organic initiators content on mechanical and thermal properties and water absorption of PBAT/EFB 60/40 wt% biocomposites were also examined. The SAH-g-EFB fiber at low WPG in presence of 1 wt% of dicumyl peroxide (DCP) initiator was found to significantly enhance the tensile and flexural properties as well as water resistance of biocomposite (up to 24%) compared with those of untreated fiber reinforced composites. The thermal behavior of the composites was evaluated from thermogravimetric analysis (TGA)/differential thermogravimetric (DTG) thermograms. It was observed that, the chemical treatment has marginally improved the biocomposites' thermal stability in presence of 1 wt% of dicumyl peroxide at the low WPG level of grafting. The improved fiber-matrix surface enhancement in the chemically treated biocomposite was confirmed by SEM analysis of the tensile fractured specimens.     

花生壳在近临界水中催化水解反应及其动力学

以花生壳为原料,AlCl3为催化剂,在近临界水中,考察了反应温度,反应时间和AlCl3浓度对还原性糖收率的影响,并建立花生壳水解反应动力学方程。结果表明,当反应温度为493 K,AlCl3的质量分数为0.02%,反应180 s,还原性糖的收率达到最大值40.4%。花生壳在近临界水中水解为一级反应,花生壳水解与还原性糖降解的活化能分别为54.03和22.44 kJ/mol,指前因子分别为2.89×103和1.26 s-1。     

海南油棕果肉中脂肪酸的成分分析

用乙醚萃取海南油棕果肉中的油脂,油脂中的脂肪酸采用氢氧化钾-甲醇溶液进行甲酯化后,利用气相色谱-质谱联用技术（GC—MS）对其中的脂肪酸成分进行分析。结果分离鉴定出4种脂肪酸成分,它们分别是棕榈酸（45．62％）、油酸（37．70％）、亚油酸（8．39％）、硬脂酸（8．29％）。其中不饱和脂肪酸高达46％以上,有进一步开发利用的潜力。     

The Effect of Fiber Bleaching Treatment on the Properties of Poly(lactic acid)/Oil Palm Empty Fruit Bunch Fiber Composites

In this work, biodegradable composites from poly(lactic acid) (PLA) and oil palm empty fruit bunch (OPEFB) fiber were prepared by melt blending method. Prior to mixing, the fiber was modified through bleaching treatment using hydrogen peroxide. Bleached fiber composite showed an improvement in mechanical properties as compared to untreated fiber composite due to the enhanced fiber/matrix interfacial adhesion. Interestingly, fiber bleaching treatment also improved the physical appearance of the composite. The study was extended by blending the composites with commercially available masterbatch colorant.