Asphaltene Instability Trends of Light and Heavy Crude Oils

In this work, two Iranian crude oils diluted in 1-methylnaphthalene (1-MN) were titrated with selected n-alkanes. Subsequently, samples were observed microscopically to determine the onset of asphaltene precipitation. A series of micrographs from de-asphaltening were used to show visible changes of the asphaltene sizes, shapes, and frequencies by addition the n-heptane to the subsamples after 5, 6, 11, and 24 hour lag times. The refractive indices (RI) of the titrated mixtures at different temperatures below and above the onset conditions were measured aiming to establish the asphaltene instability trend. Results show that for the diluted light and heavy crude oils, the onset of asphaltene precipitation is rather a gradual process with an almost constant slope of RI decrease due to the separation of asphaltene clusters from the mixture. This is a kinetically controlled process. Furthermore, the nature of the precipitant is likely to play a notable role. The rate of RI decreasing with temperature was approximately 0.0004/°C for both tested crude oils.     

A DPD study of asphaltene aggregation: The role of inhibitor and asphaltene structure in diffusion-limited aggregation

The kinetic effects of DBSA (dodecyl benzene sulfonic acid) and a linear amphihile on asphaltene aggregation was investigated, using dissipative particle dynamics molecular simulations. The simulation results indicated that without inhibitor, diffusion-limited asphaltene aggregation can be initiated by a kinetic/diffusive capture process between polar side chain groups rather than by interaction between polyaromatic rings. The most likely reason for this is that the side chains have higher diffusive mobility than the more massive aromatic ring structures. The DBSA acidic head groups adhered to the asphaltene side chain polar groups (the basic functional groups), resulting in lowered mobility of the side chain/DBSA complexes, thereby suppressing asphaltene aggregation initiation. A more mobile amphiphilic inhibitor without the aromatic ring gave a higher asphaltene aggregation rate. Adsorption of asphaltenes on a solid surface was suppressed with DBSA, due to an adsorbed mono-layer of DBSA that occupied a significant fraction of the surface area.     

偕胺肟基纤维对铜(II)的吸附动力学

对含丙烯腈结构单元的高分子材料进行 CN的改性反应,偕胺肟化后的高分子材料可作为吸附剂,用于对水溶液中的金属离子吸附去除[1 4],也可用于稀土等贵金属的富集和回收[5 6]。作者以聚丙烯腈纤维改性所得偕胺肟纤维为吸附剂,对水溶液中的Cu2+进行吸附研究,着重研究了偕胺肟纤维对Cu2+的吸附反应动力学特征。1　实验部分1 1　主要试剂与仪器偕胺肟纤维按文献[7]方法制备,Cu2+溶液由硫酸铜(AR)和蒸馏水配制,其余试剂均为分析纯。WXF 120原子吸收分光光度计(北京瑞利分析有限公司),PXD 12数字式离子计(江苏电分析仪器厂),FC 104电子天…     

Solubility Behavior of Pimozide in Polar and Nonpolar Solvents: Partial Solubility Parameters Approach

The solubility behavior of pimozide in individual solvents ranging from nonpolar to highly polar was studied. For understanding the solute-solvent interactions, the partial solubility parameters concept was utilized. Solutions containing excess drug were shaken in a water bath for 72 hours at 25 °C. After the solutions attained equilibrium, they were filtered and analyzed for drug content. A multiple regression method, using extended Hansen’s partial solubility parameters, was applied to verify the solubilities of pimozide in pure polar and nonpolar solvents and to predict its solubility in untested solvents. The three-parameter approach and the Flory-Huggins size correction term ‘B’ give predictions of solubilities with correlations up to 97%. The four-parameter approach involving proton-donor and proton-acceptor parameters was also used in fitting the solubility data. The correlations are appreciable (94%). Further, the ‘B’ term coupled with four-parameter approach was examined in order to improve the data representation, and resulted in a 1% improvement (98%) in the correlation when compared to the Flory-Huggins size-correction method. The solubility parameter obtained by this method is 10.43 H which is closer to the values obtained by theoretical methods, such as Fedors’ and Hoy’s. The resulting partial solubility parameters are δ _2d =8.85 H, δ _2p =2.17 H, δ _2a =3.15 H, and δ _2b =4.08 H, which give insights into the interaction capability of pimozide and are consistent with its chemical structure. Pimozide is a Lewis base as its δ _2b >δ _2a . The total solubility parameter of pimozide is assigned at 10.43 H. This work demonstrates for the first time the validity of the four-parameter approach coupled with the Flory-Huggins size-correction term and therefore the result is interesting.     

Adsorption of Semiflexible Chains on Nanostriped Surfaces: Monte Carlo Simulations

Monte Carlo simulations were carried out to investigate the adsorption of semiflexible chains from a semidilute solution to substrates with periodic stripes of width w. The chains are made of fused N = 10 monomers of diameter σ interacting with each other through excluded volume interactions and with the stripes via a square‐well potential of depth ε and width σ. The surface coverage was found to increase upon increasing the chain stiffness and decreases on increasing the width of the stripes. At small w, more flexible chains are adsorbed than stiff chains. Analysis of the radius of gyration for the chains showed that when w < 8σ, the component along the stripe direction is significantly larger than the others. Orientational order parameter reveals that, for small w, chains have preference to align along the stripe direction.

     

Synthesis and Adsorption Properties of Polystyrene-supported Chelating Resins Containing Heterocyclic Functional Groups

A series of new chelating resins with incorporating heterocyclic functional groups： pyridine, thiadizole, benzothizole into macroporous chloromethylated polystyrene were synthesized via hydrophilic spacer arm of polyethylene glycol containing sulfur. These chelating resins were found to show high adsorption capacities for Ag^＋, Hg^2＋, Au^3＋ and Pd^2＋, and the presence of spacer arm can enhance adsorption ability due to increase the hydrophilicity of the chelating resins.     

Surface Modification of Bituminous Coal and Its Effects on Methane Adsorption

This paper studied the role of O‐containing groups over the coal surface in methane adsorption. The coal was modified with H₂SO₄, (NH₄)₂S₂O₈ or H₂SO₄/(NH₄)₂S₂O₈), respectively, to introduce O‐containing functional groups, and characterized by proximate analysis, ultimate analysis, Boehm titration, X‐ray photoelectron spectroscopy (XPS) and nitrogen adsorption. The results of ultimate analysis, Boehm titration and XPS indicate that there were increases in terms of both the content of oxygen and the quantities of O‐containing groups over the modified coals surface, especially for the carboxyl. Nitrogen adsorption shows that the modified coals possessed higher surface area and pore volume than that of 0‐XQ. The methane adsorption data were measured at 298 K at pressures up to 4.0 MPa by the volumetric method and fitted well by Langmuir model. Experimental results implied that O‐containing groups and pore structure affected methane adsorption. The adsorption capacities decreased as increasing quantities of O‐containing groups.     

Static and Kinetic Studies on the Adsorption Behavior of Sulfadiazene

To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10^–3 mol cm^–3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl^–, SO^2– ₄ and PO^3– ₄ (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents.     

乙酸乙酯水溶液中水在3A分子筛上的吸附平衡与动力学

乙酸乙酯水溶液中水在3A分子筛上的吸附平衡与动力学;乙酸乙酯;水;吸附平衡与动力学;表面扩散系数;3A分子筛     

Experimental Investigation of the Effects of Different Parameters on the Rate of Asphaltene Deposition in Laminar Flow and Its Prediction Using Heat Transfer Approach

In this study, asphaltene deposition from crude oil on the pipe surface has been studied experimentally using a novel designed test loop. Washing technique is used to quantitatively measure the rate of asphaltene deposition during laminar flow in the steel pipe. The effects of oil velocity, asphaltene content, and surface temperature on the thickness of asphaltene deposition are investigated. The results show that the asphaltene deposition rate increases with increasing surface temperature, results in asphaltene content reduction of the flowing crude oil. As the oil velocity increases, less deposition was noticed on the surface of the pipe. Besides, thermal approach was applied to the experimental procedure which shows good agreements between the predicted thickness and the measured value from the test loop.     

渗透剂的分子体积和极性表面积分率对胰凝乳蛋白酶抑制剂2热稳定性的影响

渗透剂对蛋白质的稳定能力不仅与其极性表面积分率(fpSA)有关,而且也与其分子体积(V)密切相关.因此对于渗透剂稳定蛋白质能力的分析,需要同时考虑渗透剂的fpSA和V.为了考察渗透剂的fpSA和V对稳定蛋白质能力的影响,本文以胰凝乳蛋白酶抑制剂2(CI2)为模型蛋白,首先利用分子动力学模拟,考察了数种典型渗透剂对CI2热稳定性的影响;并根据模拟数据计算得到了渗透剂影响蛋白质热稳定性的一维结构参数;然后利用统计学双参数拟合,同时引入渗透剂的fpSA和V,建立了用于分析渗透剂稳定蛋白质能力的模型;最后利用模型分析了渗透剂的fpSA和V与其稳定蛋白质能力的关系.研究发现:利用分子动力学模拟结果定义并计算得到的一维结构参数能够较好地描述在热变性条件下渗透剂对CI2的稳定能力;所建立的模型能够很好地分析渗透剂对蛋白质的稳定能力;并且由于V和fpSA二次项的引入,可大大提高仅以fpSA为参数的模型的精度;另外,渗透剂对蛋白质的热稳定能力与其V成正比;由于拟合公式中引入了fpSA二次项,在fpSA小于0.7时,fpSA与渗透剂的稳定能力呈现负相关,但当fpSA大于0.7时,其与渗透剂的稳定能力反而呈现正相关.     

Competitive Adsorption of Methylene Blue and Rhodamine B on Natural Zeolite: Thermodynamic and Kinetic Studies

A batch system was applied to study the adsorption behavior of methylene blue (MB) and rhodamine B (RB) in single and binary component systems on natural zeolite. In the single component systems, the zeolite presents higher adsorption capacity for MB than RB with the maximal adsorption capacity of 7.95×10^?5 and 1.26×10^?5 mol/g at 55°C for MB and RB, respectively. Kinetic studies indicated that the adsorption followed pseudo‐second‐ order kinetics and could be described by a two‐step diffusion process. For the single component systems, the adsorption isotherm could be fitted by the Langmuir model. In the binary component system, MB and RB exhibit competitive adsorption on the zeolite. The adsorption is approximately reduced to 50% and 60% of single component adsorption systems of MB and RB, respectively at an initial concentration of 6×10^?6 mol·L^?1 at 25°C. In the binary component system, kinetic and adsorption isotherm studies demonstrate that the experimental data are following pseudo‐second‐order kinetics and Langmuir isotherm and kinetic data are fairly described by a two‐step diffusion model. Effect of solution pH on adsorption of MB and RB in both single and binary component systems was studied and the results were described by electrostatic interactions.     

Effects of Surface Oxygen of Activated Carbon on Alkaloid Adsorption: A Molecular Dynamics Simulation Study

The influence of the density and the type of surface oxygen on the adsorption of berberine alkaloid onto activated carbon was investigated using the molecular dynamics simulation method in vacuum. The carbon surface consisted of a basal plane of graphite and surface oxygen groups which were bonded on the graphite plane in a regular square array with various densities. Two types of surface oxygen groups, =O and —OH, were employed. The simulation results showed that the berberine alkaloids were favorable to be adsorbed on the negative charged carbon surfaces. It was indicated that the vdw attraction of the carbon surface to the alkaloid molecule dominates the adsorption only at the lower surface density of oxygen. It is also indicated that a good adsorptive selectivity for a certain berberine alkaloid can be obtained by controlling the density of surface oxygen.The adsorption simulation of berberine alkaloids onto activated carbon in the presence of water was also carried out by using a dome-shape molecular model for presenting the alkaloid/water/carbon system. It was found that the adsorption of berberine alkaloids on the activated carbon which has a higher density of surface oxygen was strongly inhibited by the presence of water.     

3D Monte Carlo Simulations of Diffusion Limited Cluster Aggregation up to the Sol-Gel Transition: Structure and Kinetics

Three-dimensional (3D) Monte Carlo simulations of diffusion limited cluster aggregation at different concentrations () show a crossover from a flocculation regime at short times to a percolation regime close to the gel time (t_g). Contrary to suggestions in the literature t_g is independent of the system size (L) for large L. The structural and temporal crossovers between flocculation and percolation take place at characteristic values of the cluster mass (m_c) and the time (t_c) which depend on . After normalisation by these characteristic values the crossovers are independent of except for very small clusters and at short times. The concentration dependence of m_c and t_c indicates that the crossover takes place at a given cumulated volume fraction of the clusters independent of . At low concentrations the -dependence of t_g is determined by the cluster growth in the flocculation regime.     

硫辛酸在三种不同树脂上的吸附热力学和动力学研究

通过静态吸附实验,研究了大孔交联聚苯乙烯树脂(XAD-4)、氧修饰超高交联聚苯乙烯树脂(NDA-100)和胺基修饰超高交联聚苯乙烯树脂(ND-90)对乙醇．水溶液中硫辛酸的吸附热力学及动力学特性,结果表明：硫辛酸在XAD-4树脂上是单层吸附,符合Langmuir等温吸附方程,吸附过程符合准一级动力学吸附方程。硫辛酸在NDA-100和ND-90树脂上的吸附也符合Langmuir等温吸附方程,但并不只是单层吸附,同时兼有毛细管凝聚和微孔填充作用,吸附过程可分为大孔和中孔区的吸附以及微孔区的吸附两个阶段,两个阶段都符合准一级动力学吸附方程。     

Adsorption of deamidated antibody variants on macroporous and dextran-grafted cation exchangers: II. Adsorption kinetics

Single and multicomponent batch adsorption kinetics were obtained for deamidated mAb variants on two commercial cation exchangers, one with an open macroporous structure--UNOsphere S--and the other with charged dextran grafts--Capto S. The adsorption kinetics for the macroporous matrix was found to be controlled largely by pore diffusion. The effective diffusivity estimated from single component data was a fraction of the mAb free solution diffusivity, and its value could be used to accurately predict the adsorption kinetics for two- and three-component systems. In this case, when two or more variants were adsorbed simultaneously, both experimental and predicted results showed a temporary overshoot of the amount adsorbed above the equilibrium value for the more deamidated variant followed by a gradual approach to equilibrium. Adsorption rates on the dextran grafted material were much faster than those observed for the macroporous matrix for both single component and simultaneous adsorption cases. In this case, no significant overshoot was observed for the more deamidated forms. The Capto S adsorption kinetics could be described well by a diffusion model with an adsorbed phase driving force for single component adsorption and for the simultaneous adsorption of multiple variants. However, this model failed to predict the adsorption kinetics when more deamidated forms pre-adsorbed on the resin were displaced by less deamidated ones. In this case, the kinetics of the displacement process was much slower indicating that the pre-adsorbed components severely hindered transport of the more strongly bound variants. Overall, the results indicate that despite the lower capacity, the macroporous resin may be more efficient in process applications where displacement of one variant by another takes place as a result of the faster and more predictable kinetics.     

Adsorption of Hexavalent Chromium Using Activated Carbon Produced from Sargassum ssp.: Comparison between Lab Experiments and Molecular Dynamics Simulations

Adsorption is one of the most successful physicochemical approaches for removing heavy metal contaminants from polluted water. The use of residual biomass for the production of adsorbents has attracted a lot of attention due to its cheap price and environmentally friendly approach. The transformation of Sargassum—an invasive brown macroalga—into activated carbon (AC) via phosphoric acid thermochemical activation was explored in an effort to increase the value of Sargassum seaweed biomass. Several techniques (nitrogen adsorption, pH_PZC, Boehm titration, FTIR and XPS) were used to characterize the physicochemical properties of the activated carbons. The SAC600 3/1 was predominantly microporous and mesoporous (39.6% and 60.4%, respectively) and revealed a high specific surface area (1695 m²·g⁻¹). To serve as a comparison element, a commercial reference activated carbon with a large specific surface area (1900 m²·g⁻¹) was also investigated. The influence of several parameters on the adsorption capacity of AC was studied: solution pH, solution temperature, contact time and Cr(VI) concentration. The best adsorption capacities were found at very acid (pH 2) solution pH and at lower temperatures. The adsorption kinetics of SAC600 3/1 fitted well a pseudo-second-order type 1 model and the adsorption isotherm was better described by a Jovanovic-Freundlich isotherm model. Molecular dynamics (MD) simulations confirmed the experimental results and determined that hydroxyl and carboxylate groups are the most influential functional groups in the adsorption process of chromium anions. MD simulations also showed that the addition of MgCl₂ to the activated carbon surface before adsorption experiments, slightly increases the adsorption of HCrO₄⁻ and CrO₄²⁻ anions. Finally, this theoretical study was experimentally validated obtaining an increase of 5.6% in chromium uptake.     

Characterization of Pressure Effects on the Cohesive Properties and Structure of Hexane and Polyethylene Using Molecular Dynamics Simulations

Molecular dynamics (MD) simulations using the OPLS‐AA force field are conducted to compute pressure‐ and molecular‐weight‐dependence of Hildebrand's solubility parameters of hexane and high‐density polyethylene (HDPE) at high pressures. The pressure dependence investigation also captures density data computed at high temperature and for external pressures ranging from 100 to 3000 bar. The effect of electrostatic potential energy contribution to cohesive energy and density is investigated and it is shown that the solubility parameter increases monotonically with increasing external pressure for both molecular mechanical models with and without electrostatic terms. Analysis of the pair distribution function is carried out versus pressure together with the influence of electrostatic energy contribution reflecting structural change of the condensed phase.

     

甲苯在多级孔丝光沸石上的吸附平衡和吸附动力学

为了考察多级孔丝光沸石中介孔的存在对丝光沸石吸附平衡和动力学的影响,选择甲苯分子作为探针分子,对其在具有不同介孔孔隙度的多级孔丝光沸石上的吸附等温线和吸附动力学曲线进行了测试。结果表明,甲苯在多级孔丝光沸石上的吸附等温线可以很好地用双位Toth吸附模型进行描述,由拟合参数以及亨利常数（K_H）和初始吸附热（Q_st）的计算得知,相对于微孔丝光沸石,介孔的引入增大了甲苯在丝光沸石内的吸附量,但减弱了甲苯与沸石表面的相互作用力;另外,甲苯在多级孔沸石表现出高的吸附速率,并随介孔孔隙度的增加而增大,反映了沸石内介孔的存在可有效促进沸石的传质能力。     

Role of Basic Surface Groups of Activated Carbon in Chlordecone and β-Hexachlorocyclohexane Adsorption: A Molecular Modelling Study

The influence of nitrogen-containing surface groups (SGs) onto activated carbon (AC) over the adsorption of chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH) was characterized by a molecular modelling study, considering pH (single protonated SGs) and hydration effect (up to three water molecules). The interactions of both pollutants with amines and pyridine as basic SGs of AC were studied, applying the multiple minima hypersurface (MMH) methodology and using PM7 semiempirical Hamiltonian. Representative structures from MMH were reoptimized using the M06-2X density functional theory. The quantum theory of atoms in molecules (QTAIM) was used to characterize the interaction types in order understanding the adsorption process. A favorable association of both pesticides with the amines and pyridine SGs onto AC was observed at all pH ranges, both in the absence and presence of water molecules. However, a greater association of both pollutants with the primary amine was found under an acidic pH condition. QTAIM results show that the interactions of CLD and β-HCH with the SGs onto AC are governed by Cl···C interactions of chlorine atoms of both pesticides with the graphitic surface. Electrostatic interactions (H-bonds) were observed when water molecules were added to the systems. A physisorption mechanism is suggested for CLD and β-HCH adsorption on nitrogen-containing SGs of AC.