Intrinsic Crosslinking and Gel-Breaking Rheokinetics of CMHEC/CTAB Systems

The intrinsic rheokinetics of carboxymethyl hydroxyethyl cellulose and cetyltrimethyl ammonium bromide (CMHEC/CTAB) synergistic fracturing fluid in static crosslinking and gel-breaking processes were studied in this work. Microrheological properties including solid–liquid balance (SLB) and elasticity index (EI) during the static crosslinking and gel-breaking processes were obtained. The effects of temperature on the crosslinking process, concentration of gel-breaker (ammonium persulfate), and temperature on the gel-breaking process were investigated. The novel intrinsic crosslinking and gel-breaking rheokinetics equations were established, respectively. The results show that the crosslinking process can be divided into two stages, and the intrinsic crosslinking rheokinetics equation can well describe EI curves during the static crosslinking process at different temperatures. The EI curves during the gel-breaking process can be well described by the intrinsic gel-breaking rheokinetics equation. The parameters for these two rheokinetics equations are well-defined and reasonable.     

Rheological and microrheological characterization of a novel amphoteric xanthan gum

A novel amphoteric xanthan gum (AXG) containing anionic carboxyl groups and cationic quaternary ammonium substituents was prepared from xanthan gum (XG) and 3-chloro-2-hydroxypropyltriethanolammonium acetate. The rheological and microrheological properties of AXG and XG solutions were studied in this work. The rheological results showed that the apparent viscosity of the 0.4% AXG solution was 5.26 times that of the 0.4% XG solution, and the AXG solution exhibited more obvious thixotropy and much stronger viscoelasticity than the XG solution. Both experiment and numerical simulations were adopted to investigate the gel-breaking process of the AXG solution, and the rheokinetics equations can well describe the evolution of complex viscosity. Moreover, the optical microrheology method was also adopted to investigate the microrheological behavior of AXG and XG solutions. The microrheological results showed that the AXG solution exhibited higher viscosity index at zero shear and a more obvious solid-like behavior than the XG solution. Good agreement is found when comparing the results obtained from microrheology to classical rheology, which verifies the feasibility of the microrheology method for measuring the solution properties, especially some properties not well described by the current rheological approach.     

A comparison of rheokinetics on static and shear crosslinking processes of xanthan gum

The crosslinking process of xanthan gum was studied under static and shear conditions. Conventional rotational rheometer was adopted to study the shear crosslinking process, and the static crosslinking process was monitored using an optical microrheometer without physical contact between the instrument and the sample. Both experiment and numerical simulation were adopted to compare the two gelation processes at different temperatures. The results showed that the effects of temperature on static and shear crosslinking processes of xanthan gum have the same trend and the rheological curves of the two gelation processes are similar in shape. The same rheokinetics equations were established to describe the two gelation processes and the simulated values are in good agreement with the experimental data. The changes of the model parameters with respect to temperature are quite similar for both the gelation processes, which verifies the feasibility of the microrheology method for measuring the static crosslinking reaction.     

Water-based drilling fluids: the contribution of xanthan gum and carboxymethylcellulose on filtration control

This study aimed mainly to evaluate the influence of xanthan gum (XG) and carboxymethylcellulose (CMC) in the filtration process of water-based drilling fluids, considering the conformational changes suffered by the polyelectrolyte with the addition of salt (NaCl) in different concentrations (0.17, 0.34 and 0.51 M). It was also evaluated the behavior of the fluid by the addition of calcite (calcium carbonate, CaCO₃). Sixteen drilling fluids were prepared with the same xanthan gum concentration (major application as thickener to transport the cuttings), but different salinities and having or not CMC and calcite at constant concentrations. This strategy was adopted to evaluate the real contribution of each additive in the control of filtration performance, frequently unclear in the papers. In general, the fluids prepared in all brines showed lower viscosities and higher filtrate loss compared to fluids of sweet water. This effect was more strong in fluids containing only XG. The addition of CMC enhanced the viscosity and reduced the filtrate loss. However, the best results were obtained when calcite was added. The results indicated that XG contribution as thickener is not enough to control efficiently the fluid filtration even in the presence of calcite. However, the addition of CMC and calcite to XG salt solution increased the viscosity and decreased significantly the filtrate loss. This result was attributed to synergistic interactions between XG, CMC and calcite.     

Experimental Validation of the Temperature-Resistant and Salt-Tolerant Xanthan Enhanced Foam for Enhancing Oil Recovery

Xanthan enhanced foam (XGF) is a newly developed chemical agent for enhanced oil recovery in high-temperature and high-salinity reservoirs. In this paper, laboratory experiments were performed to characterize the morphology and foam properties of XGF, to study its performance under different temperature and different salinity conditions, respectively. Based on simulate reservoir formation conditions of Xidaliya field, a series of research on XGF were conducted. The experimental results showed that the scanning electron microscopy of XGF reflected a more viscoelastic and stable nature of the foam system. High temperature had a great adverse impact upon the stability of XGF, and the increase of salinity in the solution helped to improve the stability of foam. The foam stability increased remarkably when XG4 is added, and an increase in ambient pressure made enhancement of foam stability became more noticeable. In the presence of crude oil, Xanthan could enhance the stability of emulsions and was more favorable to stabilize foam. XG4 enhanced foam had dramatic properties for mobility controlling and oil displacement in the porous media.     

三偏磷酸钠交联黄原胶的制备及其溶液流变性

以三偏磷酸钠(STMP)为交联剂,合成了水溶性低交联度黄原胶(XG),依据其溶液粘度优化出了最佳合成条件;考察了电解质质量分数、pH值及温度对STMP交联黄原胶(简记为SP-c-XG)溶液流变性的影响,并与XG溶液进行了对比。 结果表明,在所研究的电解质(NaCl和CaCl₂)质量分数(0~5.0%)、pH值(2~11)和温度(20~70 ℃)范围内,SP-c-XG和XG溶液的流变曲线均为假塑型,符合Herschel-Bulkley模型;其屈服值、表观粘度和动力学模量随电解质质量分数增大均先下降后上升,而随pH值的升高先升高后降低,随温度升高而降低。 SP-c-XG和XG溶液具有相似的流变性,但与XG溶液相比,SP-c-XG溶液具有更高的屈服值和表观粘度,特别是具有更强的弹性和耐温性,在油田强化采油领域具有重要应用前景。     

阴极冷却固定床电合成乙醛酸的连续过程模拟

联用反应动力学、电荷衡算和物料衡算建立阴极冷却固定床草酸电合成乙醛酸反应器模型方程.针对反应器连续化操作过程,用正交配置法数值求解该模型方程.结果表明,在连续化操作的反应初期,反应液中的乙醛酸能够较快地达到预定浓度,但继续增加反应器的长度,反应的效果不明显.该模型还模拟了分段温控和部分回流对反应的影响.结果表明,分段温控和部分回流均可较好地提高乙醛酸在阴极液中的浓度.计算结果与试验操作基本相符.该结果对阴极冷却固定床草酸电合成乙醛酸的连续化操作工艺和反应器的优化具有重要的参考意义.     

Nonlinear, electrocatalytic swimming in the presence of salt

A small, bimetallic particle in a hydrogen peroxide solution can propel itself by means of an electrocatalytic reaction. The swimming is driven by a flux of ions around the particle. We model this process for the presence of a monovalent salt, where reaction-driven proton currents induce salt ion currents. A theory for thin diffuse layers is employed, which yields nonlinear, coupled transport equations. The boundary conditions include a compact Stern layer of adsorbed ions. Electrochemical processes on the particle surface are modeled with a first order reaction of the Butler-Volmer type. The equations are solved numerically for the swimming speed. An analytical approximation is derived under the assumption that the decomposition of hydrogen peroxide occurs mainly without inducing an electric current. We find that the swimming speed increases linearly with hydrogen peroxide concentration for small concentrations. The influence of ion diffusion on the reaction rate can lead to a concave shape of the function of speed vs. hydrogen peroxide concentration. The compact layer of ions on the particle diminishes the reaction rate and consequently reduces the speed. Our results are consistent with published experimental data.     

Effect of heat treatment on thermal and mechanical stability of NaOH-doped xanthan gum-based hydrogels

Journal of Solid State Electrochemistry - Xanthan gum (XG)-based hydrogels containing sodium hydroxide (NaOH) salt were synthesized with the use of distilled water (DW) at room temperature and...     

Double Emulsions Stabilized by Xanthan in the Absence of Hydrophilic Surfactant

The preparation of double water-in-oil-in-water (W/O/W) emulsions containing xanthan gum (XG) in the absence of hydrophilic surfactant was investigated. The emulsions were prepared by the two-step emulsification process. The stability of these systems was evaluated through the evaluation of physicochemical and rheological properties. Microscopic observations in combination with particle size analysis were also performed. The obtained results show that it is possible to prepare stable double emulsions with a single polysaccharide by using the indirect process. The stability depends on the viscosity of the continuous phase and hence the concentration of XG. The apparent viscosity of the emulsions increased with the increase of XG concentration. Particle size analysis shows that the droplet sizes are directly related to XG concentration.     

Reaction and phase equilibria of esterification of isoamyl alcohol and acetic acid at 760 mm Hg

The thermodynamic behavior of esterification reaction equilibrium and vapor–liquid equilibrium (VLE) of acetic acid and isoamyl alcohol mixture and its products, isoamyl acetate and water were investigated in this study. The experiments of chemical and phase equilibria were conducted in an Othmer type equilibrium cell. Since this esterification reaction proceeds very slowly, thus, a commercial Y type zeolite, NaY catalyst, was added to accelerate reaction rate such that the reaction equilibrium will be reached sooner and before phase equilibrium is considered. Using experimental data and phase and reaction equilibrium equations, the reaction equilibrium constants were calculated at different temperatures. The experimental results showed that the reaction equilibrium constant was very slightly dependent on temperature. The experimental data were then correlated by the Wilson, NRTL, and UNIQUAC models with the consideration of association effect of acetic acid in vapor phase. The concept of transformation composition by Barbosa and Doherty [D. Barbosa, M.F. Doherty, 1987, Proc. R. Soc. London Ser. A 413, 443–459.] was applied to construct three-dimensional figures showing experimental data and the calculated composition surfaces. It is observed from figures that the reactive azeotropy described by Barbosa and Doherty does not exist for this quaternary mixture. This study provides the required thermodynamic information for the development and design of this esterification process.     

A study of the curing process of compounds based on an epoxy oligomer ED-20 and metaphenylene diamine

The possibility of application of different mathematical models used to describe the dependence of viscosity and conversion on the curing time, as well as the rheokinetics of curing of an epoxyamine compound, is considered. It is shown that viscosity growth in the process of curing is determined by the degree of conversion and temperature.     

Elaboration of spin-coated cellulose-xyloglucan multilayered thin films

In the context of developing a biomimetic model of the primary cell wall, our aim was to produce multilayered thin films composed of cellulose nanocrystals (CN) and xyloglucan (XG). We investigated the effect of XG concentrations ranging from 0.5 g/L to 10 g/L. The choice of concentration was based on rheological investigation of the XG solutions which indicated that the two lower concentrations (0.5 and 1 g/L) correspond to a semidilute regime where the polymer chains are not entangled, whereas they are entangled at the highest concentrations (5 and 10 g/L). Several processes of film preparation were tested (dipping or spin-coating, with or without a rinsing step). The film growth profiles obtained for different XG concentrations by mechanical profilometry showed that spin-coating without rinsing was the most efficient process. Results showed that at high XG concentrations (XG = 5 g/L and XG = 10 g/L) plateau values were reached after the formation of 3 or 4 bilayers, whereas growth of the multilayer structure was linear at the lower XG concentrations (XG = 0.5 g/L and XG = 1 g/L). The thickness of one CN/XG bilayer corresponded to a single layer of CN covered by a thin XG layer, despite the absence of a rinsing step between successive coatings. The importance of the XG concentration was confirmed by determining by neutron reflectivity the film architecture obtained from four XG solutions after eight successive paired coatings. The results are discussed in relation to the role of XG in the plant cell wall.     

Rheology and Rheokinetics of Photosensitive Micelle Composed of 3-Chloro-2-Hydroxypropyl Oleyl Dimethyl Ammonium Acetate and trans-4-Phenylazo Benzoic Acid

A novel rheological reversible photosensitive micelle composed of 3-chloro-2-hydroxypropyl oleyl dimethyl ammonium acetate (ODAA) and trans-4-phenylazo benzoic acid (trans-ACA) was investigated. The mixed micelle system under a suitable molar ratio (ODAA:ACA = 1.25:1) shows great viscoelastic property. Before UV irradiation, the ODAA/ACA micelle system exhibits high viscosity and good viscoelasticity. Upon irradiation by UV light (365 nm), ACA undergoes a photoisomerization from its trans to its cis form, causing a change of the molecular structure, which leads to viscosity decreases obviously; thixotropy and viscoelasticity almost disappear. The above changes of rheological properties can be reversible by exposing to visible light. Furthermore, the rheokinetics process of ODAA/ACA micelle system during UV irradiation was studied and rheokinetics equation was established, which can well describe the changing processes of viscosity and viscoelasticity. The viscoelasticity process is divided into two sections to be simulated by rheokinetics equation. In addition, these photosensitive phenomena are repeatable easily and the mechanism can be validated by UV-vis spectra.     

C.I.颜料红177中间体的制备工艺改进

本文较为系统地研究了铜粉催化剂加入方式对C.I.颜料红177中间体4,4'-二氨基-1,1'-二蒽醌-3,3'-二磺酸(DAS)合成过程中的乌尔曼偶联反应速率的影响规律。 研究结果表明,在55 ℃较佳反应温度下,先加入与溴氨酸钠质量比为2:5的铜粉,反应一段时间后再加入与溴氨酸钠的质量比为1:5的铜粉,与一次性加入与溴氨酸钠的质量比为3:5的铜粉相比较,综合反应时间可节省2~3 h。 另外,对于DAS中混有的铜盐,采取在制备过程中加入柠檬酸的方法予以去除,此举可提高DAS的纯度。 当铜粉与柠檬酸的质量比为6:1时,可使DAS中铜盐的含量小于0.001%。 此外还探究了蒸馏后滤液的剩余量对DAS收率的影响,结果表明,滤液的剩余量在20 mL时,DAS的收率在95%以上。 基于本文的研究结果提出,欲进一步提高该反应的收率,需要寻找更高效的催化剂。     

A model for the Gibbs energy of aqueous solutions of polyelectrolytes

A new model for the excess Gibbs energy of aqueous solutions of polyelectrolytes is presented and applied for the correlation of the activity of water in aqueous solutions of polyelectrolytes without as well as with an added (single) salt. The model considers the phenomenon of counterion condensation, i.e., the partial dissociation of highly charged polyelectrolytes in water. Three parameters (a binary interaction parameter between polymer segments, the equilibrium constant of the dissociation reaction and a parameter which accounts for the polymer configuration) were fitted to the experimental results. The model allows for a reliable correlation of experimental results for the osmotic coefficient of aqueous solutions of a single polyelectrolyte (without as well as with an added salt).     

城市煤气耐硫甲烷化反应器优化分析(英文)

建立了耐硫甲烷化列管式反应器的拟均相二维数学模型，运用隐式差分法求解，对日产五万立方煤气反应器的设备参数及操作参数的灵敏度进行了模拟分析。结果表明，管径对温度分布影响很大，气体入口温度及熔盐流量的影响不显著；气体入口压力及熔盐进口温度是反应器操作的灵敏因素。     

Rheological property and rheokinetics of novel photogelling fluids

A novel photorheological fluid composed of cationic Gemini surfactant N, N’-bis (octadecyl dimethyl)-1, 2-dichloride-propyl ammonium salt (C₁₈-3-C₁₈) and trans-ortho-methoxycinnamic acid (trans-OMCA) was investigated. When C₁₈-3-C₁₈ and trans-OMCA are mixed in equimolar quantities, the result is a low-viscosity Newtonian fluid with no thixotropy. After irradiation by UV light (365?nm), trans-OMCA is converted to cis-OMCA, and in turn, the solution undergoes more than 50 fold increase in the relative viscosity and exhibits shear thinning and thixotropy. The viscosity rise is associated with the formation of wormlike micellar network in the solution, which was confirmed by cryo-scanning electron microscopy (cryo-SEM). Furthermore, the rheokinetics process of the C₁₈-3-C₁₈/trans-OMCA solutions during UV irradiation was studied and rheokinetics equation was established, which can well describe the dynamic changing of the rheological properties. Critical packing parameter was introduced to explain the mechanism of photo-induced micelle transition.     

Study on the consecutive reaction kinetics of synthesis of di(2‐ethylhexyl) terephthalate under nonisothermal conditions

Since more information concerning kinetic parameters can be obtained from a nonisothermal reaction, it was selected to investigate the consecutive esterification kinetics of terephthalic acid with 2‐ethylhexanol in the presence of tetrabutyl titanate catalyst. This is an equilibrium reaction that is carried out in industry to completion by removing the water formed. It results in an automatic rise in the esterifying temperature, from 453 to 519 K. Research shows that the first step of esterification carried out in a heterogeneous system has a slow reaction rate, but the second step of esterification in a homogeneous system has a relatively fast reaction rate. Based on the quasi‐homogeneous assumption, first the differential method is presented to deal with nonisothermal reaction data. Arrhenius equations of the two steps are established by using this method. It was found that the apparent activation energy of the first step of esterification was about 55 kJ/mol higher than that of the second step. The ratio (K) of reaction rate constants of the two steps decreases gradually with the increase in the reaction temperature. An equation of K vs. temperature is also derived from Arrhenius equations. Subsequently, integral expressions of components' concentrations are used to simulate experimental results of the nonisothermal reaction as well as a three‐stage isothermal reaction. The obtained simulations show that the determined kinetic equations and the parameters are reasonable. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 577–584, 2006     

The evaporation characteristics of LiCl–KCl eutectic salt from uranium deposits using batch type vacuum distiller with temperature slope of each zones

Recovered salt can be reused in the electrorefining process and the final removed salt from uranium (U) deposits can be fed into a following U casting process to prepare ingot. Therefore, salt distillation process is very important to increase the throughput of the salt separation system due to the high U content of spent nuclear fuel and high salt fraction of U dendrites. Yields on salt recovered by a batch type vacuum distiller transfer device were processed for obtaining pure eutectic salt and U. In this study, the influence of the various temperature slopes of each zones on salt evaporation and recovery rate are discussed. From the experimental results, the optimal temperature of each zones appear at the Top Zone and Zone 1 is 850?°C, Zone 2 is 650?°C and Zone 3 is 600?°C, respectively. In these conditions, the complete evaporation of pure salt in 1.4?h occurred and the amount of recovered salt was about 99?wt%. The adhered salt in U deposits was separated by a temperature slope zone of salt distillation equipment. From the experimental results using U deposits, the amount of salt evaporation was achieved more than 99?wt% and the salt evaporation rate was about 1.16?g/min. Also, the mount of recovered salt was about 99.5?wt%.