失水山梨醇单油酸酯的柠檬酸改性研究

以乙酸为溶剂,用柠檬酸对失水山梨醇单油酸酯(span80)进行了改性。研究了原料配比、反应时间、反应温度、溶剂乙酸的量以及乙酸回流时间等因素对产物质量的影响,正交实验表明,较佳工艺条件为:柠檬酸与span80物质的量比0.4∶1,温度120℃,时间90min(蒸出乙酸以后),乙酸量为柠檬酸质量的1.5倍,乙酸回流时间为90min,蒸出乙酸的速率为0.7g/min。并以此为原料配制了2种在常温下呈液态的复合型抗氧剂,试验结果表明,其抗氧化效果超过了国外同类产品,可在油脂及含油食品中广泛应用。     

柠檬酸交联可食用红薯淀粉膜的制备和性能

本文采用浇铸法制备了柠檬酸交联红薯淀粉膜,并对膜的机械性能、吸水性、水溶性、抗甲酸溶解性等进行了测试。结果发现交联后的淀粉膜的拉伸力显著提高、吸水性增强、水溶性降低、抗甲酸溶解性增强。膜的机械性能的改善与柠檬酸的浓度、交联温度、交联时间有关,实验发现,当柠檬酸的浓度为淀粉浓度的5％,165℃处理5分钟时,膜的拉伸力比未...     

Selective separation of sodium from red mud with citric acid leaching

Selective separation of sodium with citric acid leaching from red mud has been put forward. The main factors and dealkalization mechanism by using inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and shrinking core model were studied. The results show that the dealkalization rate reached more than 95% under the following conditions: citric acid dosage of 15%, liquid-to-solid ratio of 7 mL/g, leaching temperature of 100°C, stirring speed of 300 rpm, and leaching time of 120 min. Sodium easily dissolved in the solution by citric acid leaching. The dealkalization process was controlled by internal diffusion and the apparent activation energy (E_a) was 19.43 kJ/mol.     

柠檬酸对白云母可浮性的抑制机理

为研究油酸钠体系中柠檬酸对白云母可浮性的影响规律及其与白云母的作用机理,利用红外光谱(FT-IR)、光电子能谱(XPS)、ζ电位和浮选溶液化学等方法对不同白云母样品进行了表征。结果表明,柠檬酸可明显抑制白云母的可浮性,在矿浆pH值为6、油酸钠浓度为9.20×10–4 mol/L的条件下,使用4.76×10–5 mol/L柠檬酸,白云母的回收率仅为0.40%。柠檬酸抑制白云母的可浮性主要是柠檬酸在溶液中生成的C6H7O7–和C6H6O72–等离子吸附在白云母表面,阻碍了油酸根等离子的吸附,且这些离子的吸附导致白云母表面ζ电位负向增大,削弱了油酸根等离子在白云母表面的静电吸附及化学吸附作用。此外,C6H7O7–和C6H6O72–等离子含羟基等强烈亲水基团,吸附在白云母表面会使白云母表面强烈亲水,白云母的可浮性大大降低。     

Adsorption equilibrium of citric acid from supercritical carbon dioxide/ethanol on cyano column

Supercritical adsorption equilibrium has a significant role in defining supercritical adsorption behavior. In this paper, the adsorption equilibrium of citric acid from supercritical CO2/ethanol on a cyano column was systemat-ical y investigated with the elution by characteristic point method. Equilibrium loading was obtained at 313.15 K and 321.15 K with supercritical CO2/ethanol densities varying from 0.7068 g·cm?3 to 0.8019 g·cm?3. The exper-imental results showed that the adsorption capacity of citric acid decreased with increasing temperature and in-creasing density of the supercritical CO2/ethanol mobile phase. The adsorption equilibrium data were fitted wel by the Quadratic Hill isotherm model and the isotherms showed anti-Langmuir behavior. The monolayer satura-tion adsorption capacity of citric acid is in the range of 44.54 mg·cm?3 to 64.66 mg·cm?3 with an average value of 56.86 mg·cm?3.     

The extraction of citric acid from fermentation broth using a solution of a tertiary amine

Tertiary amines are effective extractants for citric acid. The effect of diluents on the extraction is very important since it affects the distribution of citric acid, the selectivity and the phase separation properties. The distribution coefficient for citric acid is strongly temperature dependent. This makes it possible to strip the acid into water at a higher temperature. Alamine 336 dissolved in a nonpolar diluent is a suitable solvent. Pilot plant runs show that the process is technically feasible.     

Interaction and stabilization of DMF-based alumina suspensions with citric acid

The understanding of the detailed interaction between particles and dispersants in non-aqueous solutions is important for industrial applications. Herein, we report the investigation on the alumina suspension with citric acid in N,N′-dimethylformamide (DMF). The interaction was characterized by monitoring the evolution of UV-vis spectra, zeta potential values, and FT-IR spectra. The dispersion stability was examined by sedimentation test. It is found that the adsorption of citric acid on the surface of alumina particles depends on the apparent pH (pH_a) values of the solution. The adsorption follows the Langmuir type. The DMF-based alumina suspension exhibits a high stability due to the adsorption of citric acid on alumina particles, and shows the highest stability at pH_a 2.6 where the maximum adsorption occurs for citric acid.     

Innovative preparation route for uranium carbide using citric acid as a carbon source

The preparation of uranium carbide (UC) by carbothermal reduction and its sintering into dense pellets by conventional means require high temperatures for long periods. We have developed a preparation route yielding fine UC powder with significantly increased sinterability. At first, a mixture of nanocrystalline UO₂ embedded in amorphous carbon (nano-UO₂/C) was obtained by thermal decomposition of a gel containing solubilised uranyl nitrate and citric acid. Later, the nano-UO₂/C powder was treated in a conventional furnace or in a modified spark plasma sintering facility at elevated temperatures (≥1200 °C) in order to obtain uranium carbide powder. The effects of initial composition, temperature, gas/vacuum atmosphere and the overall reaction kinetics are reported.     

用柠檬酸清洗芳烃装置

主要论述利用柠檬酸的特点和清洗机理。成功地清洗了芳烃抽提装置运行2个生产周期后塔内产生的各种垢。本次化学清洗腐蚀率低，除垢率高，清洗效果好。     

柠檬酸及其盐在金属防护中的应用研究现状

综述了柠檬酸及其盐作为缓蚀剂,电镀和化学镀镀液添加剂及其在金属防护膜中的应用状况.认为柠檬酸与其他缓蚀剂的缓蚀协同性研究是柠檬酸型缓蚀剂开发的重点,柠檬酸型配位剂是替代氰化物等有毒镀液添加剂的理想选择,在稀土等无铬转化膜中添加柠檬酸盐是改进稀土转化膜耐蚀性研究的一个方向.     

Phase modulation in nanocrystalline vanadium di-oxide (VO2) nanostructures using citric acid via one pot hydrothermal method

Herein, we report the successful synthesis of different phases of VO₂ nanomaterials via a facile hydrothermal method by simply varying the molar ratio of the reducing agent (citric acid monohydrate) to vanadium precursor (vanadium (V) oxide). Six samples were synthesized with corresponding variation in molar ratio of vanadium (V) oxide to citric acid monohydrate as 1:1, 1:1.5, 1:2, 1:3, 1:4 and 1:5, respectively. The synthesized nanomaterials were characterized by phase identification, morphologies, compositional, optical, thermal, and electrical properties. The detailed characterizations confirmed the formation of single phase VO₂ (B), VO₂ (M) and amorphous VO₂ by the mere variation of relative concentrations of reducing agent. Even though the synthesis of single phase VO₂ is challenging and interestingly, a simple, one-step hydrothermal process procedure was used to produce pure phaseVO₂ without the use of inert environment or post-synthesis heat treatments.     

基于改进钛铁分光光度法测定柠檬酸液中的三价铁

基于改进钛铁分光光度法,通过pH理论计算确定缓冲溶液配比,建立了高浓度柠檬酸液中三价铁离子的测定方法。研究表明,柠檬酸浓度与所对应的缓冲溶液配比呈二次曲线关系,相关系数达到1;测定高浓度柠檬酸液中三价铁的较佳波长为480 nm,三价铁在1～10 mg/L呈良好的线性关系(r=0.999 6),加标回收率为95.5%～100.5%,重现性好。     

Anodic decomposition of citric acid on gold and stainless steel electrodes: An in situ-FTIR-spectroscopic investigation

The electrochemical decomposition of citric acid on gold and stainless steel AISI 304 (18% Cr, 10% Ni) electrodes was investigated using the technique of in situ InfraRed Reflection Absorption FTIR Spectroscopy (IRRAS) in combination with cyclic voltammetric measurements. The applied potential sweep starts from −0.265 up to +2.5 V on gold and from +0.4 up to +2.4 V on steel electrodes. The initial potentials of the anodic decomposition of citric acid could be observed on both electrode materials. Carbon dioxide was detected as decomposition product. Using stainless steel electrodes, the decarboxylation of citric acid and the forming of citrate complexes were observed. The consumption of citric acid is both due to its anodic decomposition and the generation of soluble citrate complexes of iron, nickel and chromium, resulting from the transpassive dissolution of the electrode material. At potentials more positive than +500 mV both processes are occurring simultaneously.     

The growth kinetics and properties of potentiodynamically formed thin oxide films on aluminium in citric acid solutions

The growth kinetics and properties of potentiodynamically formed thin oxide films on Al were investigated in 0.05 M citric acid solutions of different pH (5, 6 and 7) by means of potentiodynamic polarization and a.c. electrochemical impedance spectroscopy (EIS) measurements. Al showed passive behaviour within the pH range that was examined. The potentiodynamic growth of the oxide film on Al takes place due to ionic conductivity under the influence of the high electric field. Characteristic kinetic oxide film growth parameters such as the high-field growth exponential law constants (A and B), ionic conductivity through the oxide film, field strength and half barrier width have been calculated. Impedance measurements were used to determine the parameters related to the characteristic sizes and properties of oxide film. The capacitive response of the impedance spectrum was related to the thickness and dielectric properties of the barrier oxide film. The oxide film resistance values were very high, indicating that the oxide films formed under potentiodynamic conditions are highly uniform in thickness and very resistant. The anodic behaviour of Al in the citric solutions under potentiodynamic conditions were characterized by the rapid growth of the oxide film which diminished the influence of relaxation processes on the growth kinetics and structural characteristics of the aluminium/anodic oxide film/electrolyte system.     

Primary nucleation of citric acid monohydrate: influence of selected impurities

An experimental study is presented concerning solubility and primary nucleation kinetics of monohydrate citric acid from pure and selectively impure (KH₂PO₄, MgSO₄ · 7H₂O and FeSO₄ · 7H₂O) aqueous solutions. The metastable range of pure solutions is wide, ranging from 6 to 14°C, and the order of primary nucleation, equal to 2.51, is quite low. The addition of the tested impurities, which are usual fermentation aids, at concentrations lower than wt. 1%, produces negligible effects on the solubility and slightly enhances the primary nucleation rate. However, the presence of these compounds modifies the crystal habit at birth: in particular, the addition of MgSO₄ · 7H₂O and FeSO₄ · 7H₂O makes these crystals more elongated, but this effect diminishes as the crystals grow.     

Synergistic effects of rosemary, sage, and citric acid on fatty acid retention of palm olein during deep-fat frying

A study to optimize the use of oleoresin rosemary extract, sage extract, and citric acid in refined, bleached, and deodorized (RBD) palm olein during deep-fat frying of potato chips was performed using response surface methodology. Results showed that the natural antioxidants used in this study retarded oil deterioration, as evidenced by retention of fatty acid profiles. The linoleic to palmitic (C18∶2/C16∶0) ratio was chosen as the parameter for optimizing the use of natural antioxidants in RBD palm olein during deep-fat frying. Linoleic (R ²=0.946) and palmitic (R ²=0.825) acids were found to be the most important dependent variables, giving highest R ² values to various antioxidant treatments after 25 h of frying. All three antioxidants had independent significant (P<0.05) effects on the C18∶2/C16∶0 ratio. In fact, significant effects on the C18∶2/C16∶0 ratio of RBD palm olein were also given by a second-order form. A combination of 0.076% oleoresin rosemary extract, 0.066% sage extract, and 0.037% citric acid produced the optimal retention of the essential fatty acid C18∶2. In addition, a synergistic effect among these antioxidants on the fatty acid ratio of RBD palm olein was found.     

Size dependency of citric acid monohydrate growth kinetics

An experimental study concerned with the growth kinetics of citric acid monohydrate crystals is presented. Due to the properties of the system, which is very soluble, with low solid-liquid density difference and high liquid viscosity, two different techniques were used: large crystals (710-850 μm) were growtn in a fluidized bed crystallizer; small crystals, belonging to three size ranges from 90 to 355 μm, were grown in the cell of a laser light diffraction granulometer. A first order growth kinetics resulted in both cases; a comparative analysis of both the present data and those reported in the literature relevant to larger or smaller crystals, indicates that the system exhibits size-dependent growth, which increases linearly with the crystal size.     

Synthesis and characterization of novel citric acid-based polyester elastomers

In this paper we report successful simple synthesis of unique elastic polyesters by carrying out catalyst-free polyesterification of multifunctional non-toxic monomers: 1,8-octanediol (OD), citric acid (CA) and sebacic acid (SA). The chemical, physical, and surface chemical properties of the resulting copolyester polyoctanediol citrate/sebacate [p(OCS)] have been investigated. This new material was characterized by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF-MS), nuclear magnetic resonance spectroscopy (NMR), thermal analysis (TA), mechanical tests, photo-acoustic Fourier-transform infrared spectroscopy (PA-FTIR), X-ray photoelectron spectroscopy (XPS) and swelling experiments. We demonstrate that the chemical structure, morphology, physical integrity and surface chemistry of the synthesized co-polymer can be controlled by simply varying the initial acid concentration (CA/SA) in the pre-polymer. This novel p(OCS) polymer exhibits versatility in mechanical properties, hydration and hydrolytic degradation as determined by the chemical structure of the polyester elastomer.     

Characteristics and factors influencing Pb(II) desorption from a Chinese clay by citric acid

Soil contamination by heavy metals has attracted worldwide attention, since its highly toxicity and potential threaten to the human health. Thus, in this study, the desorption behaviors of Pb(II) by citric acid from a Chinese clay were evaluated. According to the results, Pb(II) removal percentage reached around 60% within 2 h. The acidic condition, relative high concentration of citric acid and contamination levels were found to be beneficial for Pb(II) desorption. During the desorption process, the originally fixed Pb(II) was first replaced by H⁺, especially at low selectivity sorption sites. The released Pb(II) was then chelated by organic ligands from citric acid.     

Synthesis of high purity Li8SiO6 using a citric acid-assisted route

Lithium oxosilicate has the highest proportion of lithium among lithium silicates, which is desirable for applications. Although Li₈SiO₆ is a stable phase, its obtention as a polycrystalline pure phase is not reported yet, probably because of the high sensitivity of the system Li₂O–SiO₂ to the synthesis conditions. In this work, we adapted a citrate-based route used for the synthesis of Li₄SiO₄ as a novel approach to the obtention of Li₈SiO₆. We found that the lowest amount of impurities is achieved by using a Li:C₆H₈O₇ molar ratio of 2.8:1, a pH value of 8.5, and a lithium excess of 20%. In a complementary way, we used the solid-state reaction method as a function of the excess of lithium and optimized the conditions that lead to a minimum amount of impurities. We found that the purest Li₈SiO₆ phase is obtained with low or no lithium excess. Samples obtained by both methods exhibited a higher purity compared to the reports available in literature. The crystal structure for this phase is confirmed by selected area electron diffraction.