Pd/C催化松脂分子间氢转移反应的集总动力学

以Pd/C为催化剂,在改进的动力学实验装置上研究了松脂分子间氢转移反应的集总动力学.在消除内、外扩散影响的条件下,在线跟踪反应产物并用气相色谱法测定反应体系组成随时间的变化,构造了Pd/C催化剂上松脂分子间氢转移集总反应网络,建立了包含单萜烯、枞酸型树脂酸、海松酸型树脂酸、对伞花烃、氢化单萜烯、脱氢枞酸、氢化枞酸型树脂酸和氢化海松酸型树脂酸等复杂反应体系的集总动力学模型,并估算了模型参数.松脂单萜烯和树脂酸的反应级数分别为1和2,并得到了松脂分子间氢转移中各反应过程的活化能.结果表明,所建动力学模型与实验数据吻合良好,并能预测反应在533 K下的集总组分浓度分布.Pd/C催化松脂分子间氢转移反应以脱氢反应为主,树脂酸的氢转移速率大于单萜烯的氢转移速率.     

Green synthesis of palladium nanoparticles using Pistacia atlantica kurdica gum and their catalytic performance in Mizoroki–Heck and Suzuki–Miyaura coupling reactions in aqueous solutions

A one‐pot green method for the synthesis of palladium nanoparticles (Pd‐NPs) supported on Pistacia atlantica kurdica (P. a. kurdica) gum is described. This natural gum is used as a reducing and stabilising agent. The formation of the Pd‐NPs/P. a. kurdica gum catalyst was verified using several techniques, such as Fourier transform infrared spectroscopy, ultraviolet–visible spectrophotometry, scanning and transmission electron microscopies, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, dynamic light scattering and wavelength‐dispersive X‐ray spectroscopy. The Pd‐NPs stabilised by P. a. kurdica gum were employed as a heterogeneous catalyst in Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions at low palladium loading (0.1 mol%) under aerobic, phosphine‐free and ligand‐free conditions in water. Product yields of up to 98%, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalyst, which can be reused at least eight times, confirm the efficiency of the catalysts in the reactions investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

Microwave-Assisted Synthesis and Characterization of Poly(itaconic acid) Grafted Gellan Gum

Poly(itaconic acid) was grafted on GG in aqueous medium under microwave irradiation using a catalytic amount of BPO. Grafted copolymers (GG-g-PIA) were characterized by FT-IR, TGA, and SEM techniques. The influence of microwave power, exposure time, and composition of the reaction mixture on extent of grafting was studied. Conditions for obtaining the highest extent of grafting were optimized. The rate of grafting was determined from weight measurements. The overall activation energy for grafting is found to be to be 28.3 kJ/mol, indicating the possibility of occurrence of the grafting process with absorption of low thermal energy.     

Use of specific polysaccharide‐immobilized monodisperse poly(glycidyl methacrylate) core–silica shell microspheres for affinity purification of lectins

Immobilization of polysaccharides (yeast mannan and gum arabic) on the macroporous poly(glycidyl methacrylate) monodisperse microspheres coated with silica (SiO₂)‐containing amino groups on the surface was used to prepare affinity sorbents for lectin purification. The efficiency of isolating mannose specific Pisum sativum lectin was demonstrated on sorbent with immobilized yeast mannan and that of galactose specific Glycine hispida lectin on sorbent with immobilized gum arabic. The microspheres with immobilized polysaccharides can be used for selecting an affinity sorbent for purification of other mannose‐ and galactose‐specific lectins. In contrast to yeast mannan, the gum arabic immobilized on the microspheres possesses much narrower specificity and is suitable for purification of only those galactose specific lectins which interact well with l ‐rhamnose or l ‐arabinose. The synthesized macroporous particles are capable of immobilizing 50 mg of polysaccharide per 1 g of the matrix, which is 10 times higher than the capacity of epoxy‐activated Sepharose 6B. That makes it possible to obtain the same lectin quantity using a column of 10 times smaller volume. Another advantage of novel affinity sorbents comparing corresponding Sepharose gels is the possibility of sorbent drying after use. Copyright © 2014 John Wiley & Sons, Ltd.     

复凝聚法制备阿维菌素微胶囊工艺研究

以阿维菌素为囊芯、明胶和阿拉伯胶为壁材,采用复凝聚法制备阿维菌素微胶囊,然后通过正交试验考察pH值、芯材比、搅拌速度、体系浓度对包囊率的影响.试验结果表明,影响包囊率的因素主次关系依次为搅拌速度、pH值、体系浓度、芯材比,优水平为搅拌速度150 r/min,pH值4.5,芯材比1.1,体系浓度2.0％.在此条件下重复试...     

羟丙基胍胶压裂液重复利用技术研究

针对南泥湾采油厂压裂施工后返排液多、处理费用高,研究了羟丙基胍胶压裂液重复利用技术.首先,以羟丙基胍胶为稠化剂,硼砂为交联剂,缓释型SS-1为破胶剂制备可重复利用的压裂液基液.然后在40℃条件下,优化重复利用时破胶液与基液的混合比例,以及向混合液中加入交联剂、破胶剂和交联促进剂的量,满足现场施工60 s内交联、3 h后破胶的要求.通过室内实验确定了重复利用压裂液体系最佳配方:破胶液与基液混合体积比为1∶3,加入交联剂硼砂质量分数0.035%～0.045%,缓释型破胶剂SS-1质量分数0.25%～0.35%,交联促进剂质量分数0.03%～0.06%.性能评价结果表明,该压裂液体系具有良好的流变性和抗剪切性,滤失量小,破胶彻底和残渣低等优良性能,实现了压裂液的重复利用.     

凝胶压井液用阴离子改性胍胶的制备及其流变性能

以环氧氯丙烷和NaHSO_3为原料,Na_2SO_3为引发剂,乙二胺四乙酸二钠(EDTA-2Na)为络合增效剂,经酸催化开环反应合成了磺酸型两性表面活性剂中间体3-氯-2-羟基丙磺酸钠,然后在弱酸性条件下与胍胶通过醚化反应制备了磺酸基羟丙基胍胶,其结构经IR表征。通过正交实验确定了合成配方和条件的最优结果,研究了反应温度、pH、改性胍胶浓度对成胶后凝胶的表观粘度影响,并测试了最佳条件下制备的凝胶和对应稀溶液的流变性能。结果表明:氧氯化锆可有效交联改性胍胶,在pH为6、温度为70℃、改性胍胶浓度为0.6%的条件下制备的凝胶具有剪切变稀性质以及较好的粘弹性。     

The behaviour of polymer solutions in extension-dominated flows,with applications to Enhanced Oil Recovery

The rheometry and flow behaviour of aqueous solutions of polyacrylamide and xanthan gum are discussed, with the expectation that the results will be of use in Enhanced Oil Recovery (EOR). The rheometrical study gives particular prominence to the dramatically high values of extensional viscosity which are possible in aqueous solutions of flexible polymers such as polyacrylamide. The effect of such factors as polymer concentration, salt concentration and mechanical degradation on rheometrical properties is outlined. Reference is also made to the qualitatively-different rheometrical behaviour experienced by comparable solutions of xanthan gum.Further evidence is advanced that some dilute polymer solutions of potential use in EOR experience abnormally high resistance in flows which are dominated by extension. Since flow through a porous medium involves a substantial extensional component, it is argued that there is justification for studying the effect of this high extensional-viscosity behaviour in a number of idealized geometries of relevance to EOR conditions. The resulting experiments indicate that, at low flow rates,shear viscosity is the dominant influence, but that, after a critical set of conditions,extensional-viscosity considerations can become all important and the observed pressure losses are against any expectation based on conventional fluid mechanics.Flow visualization studies support the pressure-drop measurements in emphasising the strong influence of high extensional viscosities in flows through tortuous geometries.This paper is dedicated to Professor Hanswalter Giesekus on the occasion of his retirement as Editor of Rheologica Acta.     

Studying the Interaction of Xanthan Gum and Pectin with Some Functional Carbohydrates on the Rheological Attributes of a Low-Fat Spread

Effects of xanthan gum (XG) (0.1 wt%) and pectin (PE) (0.5 wt%) alone and in combination with different concentrations (0.2 and 0.4 wt%) of locust bean gum (LBG), modified starch (MS), and Na-alginate (ALG) on some of the rheological characteristics of low-fat spreads, including flow behavior curves, rheological modeling, apparent viscosity, rheological modules (storage modulus (G′) and loss modulus (G″)), and delta degree (G″/G′) were studied. Results showed the power-law model was better than the Herschel–Bulkley model to describe the flow curve of dispersions. The k-value in the power-law model increased with increase in biopolymers concentration in solution. All samples exhibited shear-thinning flow behavior with a low yield stress. Dynamic oscillatory shear test showed that the spreads had a viscoelastic solid behavior with a gel-like structure. The G′ value was increased by increasing frequency from 0.03 to 15 Hz, while the G″ and G″/G′ values decreased. Also, MS in combination with XG and PE led to increase the G′ values of spreads in comparison with ALG and LBG. Moreover, microstructural and stability observations revealed that the spreads prepared with 0.1% XG-0.2% LBG significantly had the highest oiling out.     

Flowing colloidal suspensions in non-Newtonian suspending fluids: Decoupling the composite birefringence

The rheology of dilute, colloidal suspensions in polymeric suspending fluids can be studied with simultaneous dichroism and birefringence measurements. The dichroism provides a direct measure of the particle dynamics, but the birefringence is a composite property with independent contributions from the suspended particles and the polymer molecules. For suspensions where the contribution from the particles is significant, the composite birefringence must be decoupled in order to analyze the dynamics of the polymeric suspending fluid. A method to perform the decoupling is derived and then demonstrated through transient shear flow experiments with dilute suspensions ofFeOOH particles in semi-dilute, xanthan gum suspending fluids. The birefringence of the xanthan gum suspending fluid is calculated from experimental measurements of the composite birefringence and the dichroism of the suspension. To gather information on particle/polymer interactions, the calculated birefringence is compared to the birefringence of xanthan gum solutions containing no suspended particles and the dirchoism is compared to that of a suspension in a Newtonian fluid.