Relationship between the particle size distribution of commercial fully porous and superficially porous high-performance liquid chromatography column packings and their chromatographic performance

The separation efficiency and kinetics of several commercial HPLC particle types (both fully porous and superficially porous) have been investigated using a pharmaceutical weakly basic N-containing compound as a test molecule. A strong trend between the particle size distribution (PSD) of the particles and the typically employed “goodness of packing”-parameters was observed. The relative standard deviation of the PSD of the tested particles ranged between 0.05 and 0.2, and in this range, a near linear relationship between the A-term constant, the h_min-value and the minimal separation impedance was found. The experimental findings hence confirm the recent observations regarding the relationship between the narrow PSD of the recently commercialized porous-shell particles and their superior efficiency and kinetic performance. The outcome also suggests that the performance of the current generation of fully porous particle columns could be significantly improved if the PSD of these particles could be reduced.     

Role of emulsifier on the particle size and polymer particle size distribution using multiwavelength spectroscopy measurements

Latex emulsions depend strongly on the polymer composition, and particle size distribution, which in turn, is a function of the preparation of the latex and on the formulation and composition variables. This study reports measurements of particle size and particle size distribution of latex emulsions as function of the reaction time and the type and concentration of emulsifier by using the multiwavelength spectroscopy technique. Results show changes in the particle size of latex emulsions with the reaction time, obtaining larger particles and broader distributions with increasing of Tween 80 ratio. The steric stabilization provides the sole nonionic emulsifier is not enough to protect the polymer particle, causing the flocculation among the interactive particles, resulting in unstable latex. However, latex emulsions prepared with Tween 80 ratio <70 wt.% can stabilize efficiently the nucleated particles, probably due to the effects provided by both, the electrostatic and steric stabilization mechanisms. The same effect is shown in the curves of conversion (%) as a function of reaction time, resulting in slower polymerization rate for Tween 80 ratio >70 wt.%. On the other hand, smaller polymer particles, in all range of emulsifier mixture, have been obtained to higher emulsifier concentration.     

Study on the flow resistance of the dispersion system of deformable preformed particle gel in porous media using LBM-DEM-IMB method

After being injected into the porous media, the dispersion system of preformed particle gel (PPG) tends to enter high permeability regions and block water channeling passages, which forces the subsequent water to turn to the low permeability regions and thus increases sweep efficiency and enhances oil recovery. However, it is still unclear about the influence factors and the mechanisms how PPG increases water flow resistance, which limits the application of PPG in more oilfields. Therefore, the paper combines the lattice Boltzmann method (LBM), the discrete element method (DEM) and the improved immersed moving boundary (IMB) method to simulate the migration of deformable PPG in porous media. On the basis, the paper quantitatively analyzes the variation law of displacement pressure across the porous media and discusses the influence factors such as the PPG diameter, elasticity modulus and the number concentration. Results indicate that, because of the friction and retention of PPG in pore-throat, the displacement pressure across the porous media during PPG flooding is much higher than that during water flooding. In other words, the existence of PPG increases the flow resistance of injected water. Besides, the displacement pressure is always fluctuant resulting from the continuous process of PPG migration, retention, deformation and remigration. Influence factor analysis shows that the incremental value and fluctuation degree of flow resistance increase with the PPG diameter, elasticity modulus and the number concentration. The study not only provides useful reference for future PPG flooding, but also benefits the development of deformable particle flow theory.     

Effect of particle size in the hydrogenation of crotonaldehyde on supported Pt and Pt-Sn catalysts

The present work reports the effect of metal particle size on the selectivity to crotyl alcohol (S_UOL) in the liquid phase hydrogenation of crotonaldehyde over SiO₂ and a-Al₂O₃-supported Pt and Pt-Sn catalysts. It was demonstrated that, for the monometallic catalysts, a higher particle size led to a higher S_UOL, while for the bimetallic catalysts, this effect was not so important.     

Experimental study on geochemical characteristic of methane hydrate formed in porous media

The natural occurrence of methane hydrates in marine sediments has been intensively studied over the past decades, and geochemical charac-teristic of hydrate is one of the most attractive research fields. In this paper, we discussed the geochemical anomaly during hydrate formation in porous media. By doing so, we also investigated the temperature influence on hydrate formation under isobaric condition. It turns out that sub-cooling is an important factor to dominate hydrate formation. Larger subcooling provides more powerful driving force for hydrate formation. During the geochemical anomaly research, six kinds of ions and the total dissolved salt (TDS) were measured before and after the experiment in different porous media. The result is that all kinds of ionic concentration increased after hydrate formation which can be defined as salting out effect mainly affected by gas consumption. But the variation ratio of different ions is not equal. Ca2+ seems to be the most significantly influenced one, and its variation ratio is up to 80%. Finally, we theoretically made a model to calculate the TDS variation, the result is in good accordance with measured one, especially when gas consumption is large.     

Kinetic and particle size studies of emulsion polymerization of methyl methacrylate and styrene with using polyamidoamine dendrimer as seed

The emulsion polymerization of methyl methacrylate (MMA) and styrene (St) were investigated with using polyamidoamine (PAMAM) dendrimer as seed, potassium persulfate as initiator and sodium dodecyl sulfate as emulsifier. The effects of 4.0GPAMAM dendrimer concentration, initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature on the monomer conversion and polymerization rate were investigated. At the same time, the influence of the generation of PAMAM dendrimer on latex particle size was studied also. The results showed that the monomer conversion and polymerization rate increased with increasing initiator concentration, emulsifier concentration, monomer concentration, and polymerization temperature. But polymerization rate increased firstly with an increase in the 4.0GPAMAM dendrimer from 0.03 g to 0.09 g and then decreased with further increase to 0.12 g. When the concentration of 4.0GPAMAM dendrimer less than 1.449 × 10^?4 mol/L, the kinetic equation can be expressed by Rp∝[4.0GPAMAM]^0.772[SDS]^0.562[KPS]^0.589[M]^0.697, and the activation energy (Ea) of emulsion polymerization is 62.56kJ/mol. In additional, the copolymer latex particle size decreased and possessed monodispersity with increasing the generation of PAMAM dendrimer. According to FT-IR spectrum analysis, PAMAM dendrimer is successfully incorporated into the poly(PAMAM-St–MMA) latex particles.     

渣油中沥青质分子颗粒尺寸及其胶粒模型研究

分别以苯和硝基苯为溶剂测定了大庆、胜利、孤岛和辽河减压渣油沥青质、胶质和芳香分的分子量；依据球形分子模型计算了这些物质的分子尺寸；构筑了渣油中沥青质胶粒（胶团）模型，并依此计算了渣油中沥青质胶粒尺寸。结果表明，以硝基苯为溶剂所测沥青质分子量更能反应沥青质化学结构的实质；就原始沥青质来说，以苯为溶剂测得的沥青质分子直径为3.8 nm～5.0 nm,以氯代苯为溶剂测得的分子直径为3.2 nm～3.7 nm,以硝基苯为溶剂测得的分子直径为2.8 nm～3.2 nm；辽河、胜利与大庆减压渣油中沥青质的胶粒直径为10.0 nm～11.0 nm，孤岛减压渣油中沥青质的胶粒直径为9.0 nm～10.0 nm。     

微乳法制备纳米级WO3粉体

以最佳重量比６：４的∈ＣＨ２－ＣＨＯＨ）ｎ和ＣＨ３Ｃ１０Ｈ２２ＣＯＣＨ（ＯＨ）ＣＨ（ＯＨ）ＮＨ２作为混合型乳化剂，在二甲苯／水体系中首次制备了纳米级三氧化钨粉体，确定了最佳反应条件。在不同温度下处理得到的纳米级粉体为分散的规则球形粒子（最小尺寸为１５ｎｍ）。用透射电镜和Ｘ－Ｒａｙ衍射对各种温度处理得到的ＷＯ３粉体进行了分析。所制备的ＷＯ３纯度为９９．９６％。     

Crosslinking network structure governing particle shape and size distribution by one-step emulsion polymerization in the presence of particle coagulation

In this study, sub-200?nm, crosslinked latex particles with a narrow particle size distribution were prepared by one-step emulsion polymerization in the presence of particle coagulation. The relationship between the particle shape and particle coagulation was investigated by varying the time of crosslinking network structure formation and particle coagulation. Particles with irregular shapes such as doublet, triplet, and ellipsoid were obtained using divinylbenzene (DVB) and ethylene glycol dimethacrylate (EGDMA) as the crosslinking agents, because the crosslinking network structure of particles was formed before the particle coagulation. In contrast, latex particles with a uniform spherical shape were also prepared using triallyl isocyanurate (TAIC) or dihydrodicyclopentadienyl acrylate (DCPA) as the crosslinking agents by delaying the time of crosslinking network structure formation. Alternatively, uniform spherical latex particles were prepared by bringing forward the particle coagulation time using cationic initiator, 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). This study presents a new idea that would further broaden the application of particle coagulation in emulsion polymerization.     

预混天然气在多孔介质燃烧器中的燃烧与传热

在一台小型渐变型多孔介质燃烧器上进行了预混天然气燃烧与传热试验研究,探讨了天然气速度和多孔介质厚度对多孔介质燃烧室的温度分布、排烟温度和流动阻力的影响。结果表明,天然气在渐变型多孔介质燃烧器中燃烧稳定,燃烧室与水冷夹套间的换热受天然气速度和多孔介质厚度影响,换热效果比空管中燃烧明显增强,同时预混天然气通过多孔介质的进出口压差随着天然气速度和多孔介质厚度的增加而增加。     

Synthesis of large-scale,narrowly dispersed,highly cross-linked,and spherical latex particles via one-step emulsion polymerization through particle coagulation

Particle coagulation technology is a facile approach to prepare large-scale and narrowly dispersed polymer particles. However, diverse shapes such as ellipsolid, snowman, dumbbell, and trimer among others were obtained if the cross-linker was directly added into the initial reaction mixtures due to the restriction of the highly cross-linking particle fusion process. In this study, we prepared sub-200?nm, narrowly dispersed, highly cross-linked, and spherical latex particles using particle coagulation technology by controlling the relation between the cross-linking net formation and particle coagulation. Depending on the addition time or feeding rate of the cross-linker (divinylbenzene, DVB), the particles with different sizes or shapes were obtained. The later the addition start time of DVB, the narrower the particle size distribution of the latex particles. Alternatively, the increase of the continuing feeding time could also be used to decrease the width of particle size distribution of the ultimate latex. In addition, narrowly dispersed and spherical latex particles also could be directly obtained by advancing the particle coagulation time using 2, 2′-Azobis (2-methylpropionamidine) dihydrochloride as a cationic initiator. Our study presents a new method that will further widen the fields of application of particle coagulation technology.     

Effect of surfactant types on particle size and morphology of flame-retardant zinc borate powder

Zinc borate is a boron-containing chemical material that is used to increase the flame retardancy of polymeric materials, dyes, cables, fabrics, carpets, and the internal parts of automobiles and planes. Commercially used zinc borate, which has the formula of 2ZnO·3B ₂ O ₃ ·7H ₂ O, has a particle size between 10 and 20 μm. However, recent studies have shown that nanosized flame retardants have more superior flame retardancy and less negative effects on mechanical properties than microsized flame retardants. Nanosized flame retardants disperse more homogeneously and even low quantities are sufficient to provide high flame resistance. In this study, nano zinc borate powder was synthesized by a wet chemical method and the effects of nonionic, anionic, and cationic surfactants on the particle size and morphology of the zinc borate particles were investigated. Chemical purity and physical structures of the synthesized zinc borate powder were analyzed by XRD, FTIR, TG-DTA, TEM, and Zetasizer. The analysis results showed that the zinc borate powder had a chemical formula of 2ZnO·3B ₂ O ₃ ·7H ₂ O. TEM and Zetasizer results indicated that the nano zinc borate powder, which had nanoscale particle size distribution with needle- and flake-like structures, was synthesized using nonionic, anionic, and cationic surfactants.     

Performance study on particle size variables for nano multiple emulsions

Multiple emulsions are of growing interest as potential delivery vehicles for active constituents. The objective of this study was to encapsulate a water-soluble substance as a functional ingredient in the water-in-oil-in-water (W/O/W) multiple emulsions with nano droplets, and the resultant characterizations have been determined. Emulsions have been generated using ultrasonic with different time, the prepared multiple emulsions have been characterized with microscopic analysis, differential scanning calorimetry, encapsulation efficiency, and rheology. Moreover, droplet size and conductivity analysis have been determined to measure stability. Results showed that multiple structures exist after ultrasonic. Furthermore, these nano multiple emulsions presented encapsulation efficiencies up to 60%, while oil droplets size was 320 nm. Rheology analysis showed dissimilar features of distinct particle size, while droplet size and conductivity analysis indicated a similar trend with the passage time. As a conclusion of this study, the results were encouraging towards development of a nano multiple emulsion encapsulate water-soluble active ingredient for cosmetics.     

Studies on the particle size control of gelatin microspheres

A series of gelatin microspheres (GMs) were prepared through emulsification-coacervation method in water-in-oil (w/o) emulsions. The influence of preparation parameters on particle size, surface morphology, and dispersion of GMs was examined. The studied preparation parameters include concentration of gelatin solutions, concentration of the emulsifier, w/o ratio, emulsifying time, stirring speed, and so on. The surface morphology, dispersion, and particle sizes of GMs were determined by the scanning electron microscopy (SEM), SemAfore 4 Demo software, and particle size distribution graphic charts. The experimental results indicated that increasing the concentration of gelatin solution would increase the particle size of GMs. When the solution concentration increased from 0.050 to 0.200 g/mL gradually, the particle size increased correspondingly. The relationship between the two quantities was linear. On the contrary, increasing the concentration of the emulsifier would decrease the particle size of GMs. Furthermore, the particle size reduced quickly at initial time and slowed down latterly. With the increase of emulsifier concentration from 0 to 0.020 g/mL, themean diameters ofGMsdecreased from 17.32 to 5.38 μm. However, the particle size dwindled slowly when emulsifier concentration was higher than 0.020 g/mL. The excellent result was obtained with the condition of 0.050 g/mL of emulsifier concentration, 0.100 g/mL of gelatin solution concentration, 1/5 of w/o ratio, 10 min of emulsifying time, and 900 r/min of the stirring speed. The GMs prepared at this condition had the smallest sizes, the narrowest size distribution, the best spherical shape, and fluidity. The w/o ratio has the same influence on particle size of GMs as that of gelatin solution concentration. With the increase of w/o ratio, the average particle sizes increased linearly, and the surface of microspheres become smoother as well. It is supposed that w/o ratio can be used to change the diameters and surface morphologies of GMs. The emulsifying time has little influence on the mean diameters of GMs, but it affects the dispersion of GMs apparently. When the emulsifying time was shorter than 5 min, the GMs had bad dispersion. After increasing the emulsifying time to 13 min, the dispersion of GMs changed greatly, whereas the dispersion of GMs became bad again when the emulsifying time was longer than 13 min. According to the experimental results, 13 min was considered to be the best emulsifying time. The stirring speed has the similar influence on GMs’ morphologies as that of emulsifying time. Slow stirring rate made large size distribution and bad spherical shape of GMs; excessive stirring speed results in aggregation among GMs likewise. The smaller size distribution and better spherical shape of GMs were observed under the stirring rate between 500 and 1500 r/min by SEM. In conclusion, increasing the concentration of gelatin solution or w/o ratio would increase the particle sizes of GMs, increasing the concentration of the emulsifier would decrease the sizes of GMs at proper emulsifying time, and stirring speed would get the best spherical shape of GMs. These are the basic laws governing the design and manufacture of the GMs. __________ Translated from Acta Polymerica Sinica, 2008, 8 (in Chinese)     

加热速率和粒径对聚乙烯在超临界水中转化的影响

随着塑料制品的广泛使用,废塑料在中国每年呈递增趋势,在城市垃圾中特别是沿海地区废塑料的质量分数己增加到8％～10％,而体积分数达到30％以上,造成严重的“白色污染”。回收利用废塑料不仅可以解决环境污染问题,而且可以将废弃物转化为资源。废塑料降解油化可以得到价值较高的液体燃料或化工原料,是一种较为理想的回收利用方法。     

On the evolution of particle size average and size distribution in suspension polymerization processes

The dispersion of methyl methacrylate (MMA) and its suspension polymerization were used as models to elaborate the evolution of particle size average and size distribution in the course of suspension polymerization. The underlying mechanisms for the occurrence of the dynamic and static steady states in the population of drops were defined and their effects on the evolution of drop/particle size average and size distributions were examined. The characteristic intervals of suspension polymerizations (transition, steady-state, growth, and identification) were elaborated. The formation of satellite droplets and their evolution in the course of polymerization were also discussed.     

Effect of particle size on pyrolysis characteristics of Elbistan lignite

In this study, the relationship between particle size and pyrolysis characteristics of Elbistan lignite was examined by using the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. Lignite samples were separated into different size fractions. Experiments were conducted at non-isothermal conditions with a heating rate of 10°C min⁻¹ under nitrogen atmosphere up to 900°C. Pyrolysis regions, maximum pyrolysis rates and characteristic peak temperatures were determined from TG/DTG curves. Thermogravimetric data were analyzed by a reaction rate model assuming first-order kinetics. Apparent activation energy (E) and Arrhenius constant (A _r) of pyrolysis reaction of each particle size fraction were evaluated by applying Arrhenius kinetic model. The apparent activation energies in the essential pyrolysis region were calculated as 27.36 and 28.81 kJ mol⁻¹ for the largest (−2360+2000 μm) and finest (−38 μm) particle sizes, respectively.     

Experimental investigation of methane hydrate decomposition by depressurizing in porous media with 3-Dimension device

In order to simulate the behavior of gas hydrate formation and decomposition, a 3-Dimension experimental device was built, consisting of a high-pressure reactor with an inner diameter of 300 mm, effective height of 100 mm, and operation pressure of 16 MPa. Eight thermal resistances were mounted in the porous media at different depthes and radiuses to detect the temperature distribution during the hydrate formation/decomposition. To collect the pressure, temperature, and flux of gas production data, the Monitor and Control Generated System (MCGS) was used. Using this device, the formation and decomposition behavior of methane hydrate in the 20～40 mesh natural sand with salinity of 3.35 wt% was examined. It was found that the front of formation or decomposition of hydrate can be judged by the temperature distribution. The amount of hydrate formation can also be evaluated by the temperature change. During the hydrate decomposition process, the temperature curves indicated that the hydrate in the top and bottom of reactor dissociated earlier than in the inner. The hydrate decomposition front gradually moved from porous media surface to inner and kept a shape of column form, with different moving speed at different surface position. The proper decomposition pressure was also determined.     

An investigation into the relationship between the electrical conductivity and particle size of polyaniline in nano scale

Polyaniline nanoparticle (nPANI) was successfully synthesized through ultrasonic-assisted reverse microemulsion polymerization method. The effect of four parameters including concentration of aniline (ANI) as monomer, molar ratio of dodecybenzene sulfonic acid (DBSA) as surfactant to ANI, molar ratio of ammonium peroxydisulfate (APS) as oxidant to ANI and polymerization temperaturewere systematically studied in terms of the structural characterizations of nPANI by applying the Taguchi method of experimental design. Data analysis indicated that there is a dependency between conductivity and particle size in the nanoscale; the maximum conductivity of nPANI was obtained when the diameter of the particles was 30?nm.