NMR imaging of the distribution of the liquid phase in a catalyst pellet during alpha-methylstyrene evaporation accompanied by its vapor-phase hydrogenation

This communication reports the first application of NMR imaging to study the progress of a multiphase heterogeneous catalytic reaction in situ. Various stationary regimes of alpha-methylstyrene (AMS) hydrogenation on a single Pt/gamma-Al2O3 catalyst pellet have been investigated. The two-dimensional maps of the liquid-phase distribution within the pellet have been obtained in the course of the catalytic reaction, with the pellet temperature rising up to 185 degrees C. The large liquid-phase concentration gradients have been shown to exist under conditions of liquid AMS evaporation accompanied by its vapor-phase hydrogenation. It has been demonstrated that despite a substantial broadening of the NMR lines of liquids permeating porous solids the quantification of the relative amounts of AMS and the major reaction product cumene with spatial resolution across the pellet is feasible.     

Effect of calcium on the pellet height response of Tetrahymena cilia

The pellet height response (a measure of the increase in height of the pellet of cilia obtained by brief centrifugation in the presence of ATP as compared to the absence of ATP) of Tetrahymena cilia prepared by deciliation in the presence of Ca2+ is sensitive to the concentration of free Ca2+ during the pellet height assay. The magnitude of the increase in pellet height and the sharpness of the pellet boundary both increase markedly with increasing [Ca2+]. The half-maximal effect is attained at a free [Ca2+] of about 1.5 x 10(-7) M. The pellet height assay thus measures a Ca2+-sensitive component of the ciliary motile system. The possibility that this is the Ca2+-sensitive orientation system is discussed.     

A novel theoretical model for calculating the effective diffusivity of gases in a porous pellet composed of two different grains

Effective diffusivity of gases is an important property when modeling the physicochemical processes occurring in a pellet. Calculating effective diffusivity in a pellet composed of a mixture of particles is a difficult task. In this paper, a theoretical model is presented in order to describe the diffusion of gases in a porous pellet made up of a mixture of two kinds of solid grain. Solid grains can either be fully dense and thus non-porous or contain pores, with a grain being sub-divided into sub-grains. The results predicted by the model have been evaluated and validated by use of experimental data obtained by reduction of cuprous sulfide in the presence of lime. Finally, the effects of structural properties and operating conditions on the effective diffusivity of the gases in the pellet have been evaluated.     

Inhibition of corneal neovascularization by rapamycin

The purpose of this study was to determine whether rapamycin could inhibit corneal angiogenesis induced by basic fibroblast growth factor (bFGF). Using human dermal microvascular endothelial cells (HDMECs), we examined the effect of rapamycin on cell proliferation and migration, and the expression of vascular endothelial growth factor (VEGF). The rabbit's eye was implanted intrastromally into the superior cornea with pellet containing bFGF for the control group and pellet containing bFGF and rapamycin for the rapamycin group. Biomicrographically, corneal angiogenesis was evaluated for 10 days after pellet implantation. The neovascularized cornea also was examined histologically. bFGF induced corneal neovascularization was significantly reduced by treatment with rapamycin. Using in vitro model, rapamycin strongly inhibited bFGF induced proliferation, migration, and VEGF secretion of HDMECs. We could observe that the bFGF induced corneal angiogenesis was inhibited by rapamycin in a micropocket rabbit model. The score of neovascularization was significantly decreased in the rapamycin group than in the control group at 10 days after pellet implantation. Histologically, the cornea of rapamycin group also showed much less new vessels than that of control group. Collectively, rapamycin appears to inhibit bFGF induced angiogenesis in a rabbit corneal micropocket assay and may have therapeutic potential as an antiangiogenic agent.     

Oxidation kinetics of iron sulfide in the form of dense plate,pellet and single particle

The oxidation behaviours of pyrrhotite in the form of dense plate, pellet and single particle were compared. In the oxidation of dense plate of FeS, preferential oxidation of iron took place to form a dense oxide layer in the earlier stage of oxidation, and the subsequent oxidation accompanying the evolution of SO₂ gas proceeded after the composition of pyrrhotite attained Fe_0.9S. In the oxidation of FeS pellet, both the above reactions take place simultaneously because the pellet consists of fine particles. In the oxidation of single particle of small size, ignition of the particle occurred due to the heat of oxidation, and the particle melted in a very short time less than 1 second.     

Characterization of dual layered pellets for sustained release of poorly water-soluble drug

The aim of this study was to develop pellet formulations that could be used to improve the dissolution and bioavailability of a poorly water-soluble model drug, cisapride. Six different types of pellets were prepared by coating sugar spheres in a fluidized bed coater. When the sugar spheres were single layered containing cisapride and solubilizer such as polysorbate 80, the resulting pellets provided an instant release of cisapride in the simulated gastric fluid. Dissolution tests carried out in the simulated intestinal fluid showed that there were negligible amounts of cisapride released, regardless of the pellet formulation. To succeed in attaining dissolution and the sustained release of cisapride at a neural pH, the single layered pellets were coated again with a coating suspension containing Eudragit RS 30D and L 30D. Scanning electron microscopy revealed that the dual layered pellets had a crack-free and spherical surface. Interestingly, the dual layered pellets provided the sustained release of cisapride in both the simulated gastric and intestinal fluids. The composition and components of the dual layers were found to be key parameters affecting the pattern of cisapride dissolution. Significant improvement in the bioavailability of cisapride was achieved when the dual layered pellets were administered orally to dogs. Overall, these results suggest that the dual layered pellets have potential as a sustained release dosage form for poorly water-soluble drugs.     

Reactions of mixtures in supported catalysts: I. Models for catalyst deactivation and support pore size change and a single pellet behavior

A general model is presented for reaction mixtures undergoing catalytic reactions that are affected by catalyst deactivation. A continuum approach is used to represent the mixtures in terms of molecular size. The model accounts for the pore size exclusion effect, the change of pore size with deactivation along the entire pore length, and the effect of multilayer deposition of coke or metals on residual activity. The model also accounts for all possible reaction paths leading to all products and intermediates. Simulation results are presented for typical reaction mixtures. The results show that a larger pellet gives a higher residual activity for smaller molecules whereas a smaller pellet yields a higher activity for larger molecules. They also show that pellet size has little effect on the change of pore diameter with time.     

In-line prediction of drug release profiles for pH-sensitive coated pellets

A new method for the prediction of the drug release profiles during a running pellet coating process from in-line near infrared (NIR) measurements has been developed. The NIR spectra were acquired during a manufacturing process through an immersion probe. These spectra reflect the coating thickness that is inherently connected with the drug release. Pellets sampled at nine process time points from thirteen designed laboratory-scale coating batches were subjected to the dissolution testing. In the case of the pH-sensitive Acryl-EZE coating the drug release kinetics for the acidic medium has a sigmoid form with a pronounced induction period that tends to grow along with the coating thickness. In this work the autocatalytic model adopted from the chemical kinetics has been successfully applied to describe the drug release. A generalized interpretation of the kinetic constants in terms of the process and product parameters has been suggested. A combination of the kinetic model with the multivariate Partial Least Squares (PLS) regression enabled prediction of the release profiles from the process NIR data. The method can be used to monitor the final pellet quality in the course of a coating process.     

C302铜基甲醇合成催化剂颗粒设计Ⅱ. 颗粒结构对Lurgi型合成反应器性能的影响

基于本文（I）报的研究结果，以固定床反应器二维非均相数学模型为基础，模拟考察了C302铜基甲醇合成催化剂颗粒设计对Lurgi型合成反应器性能的影响。结果表明，由于颗粒结构设计改变了粒内反应－扩散耦合行为的相互匹配关系，使得催化剂的宏观反应活性发生变化，进而对反应器的操作性能产生显著的影响（包括反应器生产能力、温度和浓度分布特性、床层压力降和热点温度等），为提高反应器的生产能力和改善反应器的操作性能，进行催化剂颗粒的适宜结构设计是非常必要和有价值的。     

Laboratory-scale production of biofuel pellets from electron beam treated Scots pine (Pinus silvestris L.) sawdust

The effect of electron beam (EB) treatment on pine sawdust used as raw material for fuel pellets was studied. Dry sawdust was EB treated at different dosage levels up to 100 kGy. The effect of EB treatment on fatty and resin acid composition was studied for different dosage levels and compared to untreated sawdust. Pellets were pressed in a laboratory single pellet press unit according to a D-optimal, response surface modeling (RSM) experimental design, where sawdust moisture content and die temperature were varied independently for EB treatment dosages of 0, 18.2 and 48.9 kGy. The responses of the designed experiment were density and strength for the produced pellets.The results showed that the free fatty and resin acid content in the sawdust initially decreased with increasing EB doses but at the highest EB doses it increased. The total content of extractives however initially increased and then decreased with increasing EB dose. Pellets made of EB treated sawdust had a significantly (at 95% confidence level) higher density and compressive strength than pellets made from untreated sawdust. EB treated sawdust behaved similarly to stored (mature) sawdust as a pellet raw material. Thus, EB treatment opens the possibility for controlled ageing (maturation) of pellet raw materials.     

Morphogenesis of polyoxometalate cluster-based materials to microtubular network architectures

Pressed pellets of polyoxometalate (POM)-based materials are shown to undergo morphogenesis to produce microtubular network architectures without the need for a large single crystal precursor. The compression of the POM material into a pellet lowers the solubility sufficiently to allow tube initiation and growth from POMs that would otherwise be too soluble in their native crystalline state, thus yielding hollow, highly controllable, tubes of diameter 10-100 μm.     

Diffusion Mechanism of Carbon Dioxide in Zeolite 4A and CaX Pellets

The adsorption kinetics and equilibria of CO₂ in commercial zeolite 4A and CaX pellets were theoretically and experimentally studied by a gravimetric method in the range of 273–313 K and 0.0–0.8 atm. The diffusion mechanism of an adsorbate into a pellet is composed of micropore and macropore diffusion due to the bidisperse structure of the pellet. When one diffusion mechanism played a more important role than the other in determining the overall diffusion rate, the diffusion rate was estimated by the nonisothermal monodisperse diffusion model (NMDM). However, when the combined effects of both mechanisms controlled the overall adsorption kinetics, the experimental uptake was analyzed by the nonisothermal bidisperse diffusion model (NBDM). The CO₂ diffusion in zeolite 4A pellets was controlled by micropore diffusion within the experimental pressure and temperature ranges. However, both macropore and micropore diffusion contributed to CO₂ diffusion in the zeolite CaX pellet. The overall CO₂ diffusion rate in zeolite CaX became faster as pressure increased mainly due to its highly favorable isotherm in the zeolite CaX. The micropore diffusion time constant of CO₂ in the zeolite CaX pellet was approximately one hundred times greater than that in the zeolite 4A pellet. In addition, the activation energy of micropore diffusion of CO₂ diffusion in the zeolite CaX pellet was smaller than that in the zeolite 4A pellet. In this study, the dimensionless parameter, , indicating the relative importance of macropore and micropore diffusion, was modified to consider non-zero coverage as an initial condition for each step in the gravimetric method. When is greater than 100, the overall adsorption rate is controlled by macropore diffusion. However, in cases where is less than 0.1, micropore diffusion is the dominant mechanism in the overall adsorption rate. In the case of a system with between these values, both macropore and micropore diffusion contributed to the overall diffusion rate.     

在胆酸盐介质中用氨羧配位剂溶解胆红素钙的动力学研究

以胆红素及其钙盐为主要成分的色素型胆结石病在国内为常见病,多年来曾研究用钙配位剂溶石的可能性,但效果不明显,主要由于对配位剂溶石机理了解不够。为此本文在模拟胆汁背景条件下,用氨羧配位剂溶解模拟结石的胆红索钙压片进行了动力学研究,其结果有利于阐明胆色素结合配位溶解的机理和决定溶石效果的因素。     

Thermal Transfer During the Activation Process in LiSi/FeS2 Thermal Batteries

Thermal batteries(TBs) as primary power sources are widely applied in defense and military affairs, and used in electronic packages and nuclear weapons. The activation time(AT) of TBs restricts the reactive speed of them. Therefore, it is a remarkably important parameter and needs to be studied in detail. In our previous study, the thermal transfer model has already been found during the activation process in TBs. In this work, the experimental TBs were fabricated and tested for validating the model. The error between the average value of test and calculation value from this model is less than 1%. As a result, the thermal transfer function for the activation process in the given TBs[FeS₂/LiCl-KCl(MgO)/LiSi containing Fe/KClO₄ heat pellet] is suggested.     

氨氮与磷在三种人工湿地填料上的吸附动力学

利用吸附动力学实验研究了浮石、陶结和陶粒对氨氮和磷的吸附动力学特征.结果表明:浮石对氨氮与磷的吸附容量明显比陶结和陶粒的大.人工湿地填料浮石和陶粒对氨氮与磷,以及陶结对氨氮的等温吸附动力学特征均可以用准一级、准二级和Bangham模型加以描述.其中浮石对氨氮和磷以及陶结对氨氮的吸附以化学吸附反应控制为主,而陶粒对磷的吸附过程则以扩散反应控制为主.三种填料对氨氮和磷的吸附均以表面吸附为主.     

The structural model for liquid-solid reaction of mesoporous powder

The reaction kinetics of the mesoporous powder, MCM-TP, anchored with synergistic extractant TOPO-P204, with Pd²⁺ in spent fuels have been investigated. The results showed that the reaction rate was independent of pellet size, which suggested that the powder pellet was highly porous and was composed of plate-like “grains”. This analysis was confirmed by observing the surface and cross section of the pellet with SEM. It provided the physical basis for establishing the liquid-solid reaction model of mesoporous powders: P-G^* model. The calculated curves from the model were in good agreement with the experimental results.     

Influence of production variables on the sphericity of melt pellets

This paper reports the influence of post-melt impeller speed, post-melt processing time, binder concentration and particle size of bulk material on the sphericity of pellets produced by melt pelletization in a high shear mixer. Lactose was used as the bulk material with polyethylene glycol 3000 as a meltable binder. The sphericity of pellets was found to be affected by post-melt impeller speed and post-melt processing time. Binder concentration and particle size of bulk material had a lesser effect on pellet sphericity. The melt pelletization process can be divided into two spheronization phases (a fast initial rate, followed by a slower rate). The change in the spheronization rate was associated with the pellet size, porosity and flow pattern of the processing material. The present study established a bi-exponential mathematical model to relate the pellet sphericity with post-melt specific energy consumption. The relationship of pellet sphericity with post-melt specific energy consumption was independent of the effects of the production variables.     

A generalized mathematical model for non-catalytic gas-solid reactions

Based on a general classification and characteristic comparison of the existing models, a new model for non-catalytic gas-solid reactions is proposed and a general formulation for the model in terms of the solid conversion, X, is presented in this paper. The model, referred to the generalized model, is demonstrated to be applicable to any solid reactant of general structure ranging from highly porous to nonporous materials. It is shown that the generalized model incorporates the grain and pore structure for a solid pellet and can be reduced to the grain and random pore models as extreme cases.     

Effects of Pellet Characteristics on L-Lactic Acid Fermentation by R. oryzae: Pellet Morphology,Diameter, Density,and Interior Structure

The effects of pellet morphology, diameter, density, and interior structure on L-lactic acid fermentation by Rhizopus oryzae were characterized for different inoculum sizes and concentrations of peptone and CaCO₃. Inoculum size was the most important factor determining pellet formation and diameter. The diameter decreased with increasing inoculum size, and larger pellets were observed for lower inoculum sizes. Peptone concentration had the greatest effect on pellet density, which increased with increasing peptone concentration. L-lactic acid production depended heavily on pellet density but not on pellet diameter. Low-density pellets formed easily under conditions of low peptone concentration and often had a relatively hollow structure, with a thin condensed layer surrounding the pellet and an extraordinarily loose biomass or hollow center. As expected, this structure greatly decreased production. The production of L-lactic acid increased until the density reached a certain level (50–60 kg/m³), in which the compact part was distributed homogeneously in the thick outer layer of the pellet and loose in the central layer. Homogeneously structured, denser pellets had limited mass transfer, causing a lower overall turnover rate. However, the interior structure remained nearly constant throughout all fermentation phases for pellets with the same density. CaCO₃ concentration only had a slight influence on pellet diameter and density, probably because it increases spore germination and filamentous hypha extension. This work also provides a new analysis method to quantify the interior structure of pellets, thus giving insight into pellet structure and its relationship with productivity.     

A Hierarchical Structural Model for the Interpretation of Mercury Porosimetry and Nitrogen Sorption

A new model of interpretation for the mercury porosimetry experiment has been presented. The void space of a porous solid is modeled by separate representations of both the macroscopic (>10 μm) and the mesoscopic (<10 μm) length scale properties of the material. Complementary information from nitrogen adsorption, on the mesoscopic scale, and NMR imaging, on the macroscopic scale, is used in conjunction with the mercury porosimetry data to provide a more accurate structural representation of a porous medium. The model is therefore able to probe spatial geometric changes in pellet structural architecture over many length scales during processes such as catalyst manufacture and the deactivation of catalysts by coke deposition. Copyright 2000 Academic Press.