超临界流体快速膨胀法制备微细颗粒

利用超临界流体快速膨胀法(RESS)制备微细颗粒,是近年来兴起的一种很有应用前景的新的粉体技术。笔者就该技术的过程原理、典型实验装置、过程条件的影响因素、近年来国内外的主要研究成果及其存在的问题进行了论述。     

用含夹带剂丙酮的超临界CO2快速膨胀法制备灰黄霉素的微细颗粒

Griseofulvin (GF) is an antifungal drug whose pharmaceutical activity can be improved by reducing particle size. In this study the rapid expansion of supercritical solution (RESS) was employed to micronize GF.Carbon dioxide with cosolvent acetone was chosen as a supercritical mixed solvent. The solubility of GF in super-critical CO2 with cosolvent acetone was measured using a dynamic apparatus at pressures between 12 and 32 MPa,temperatures at 313, 323 and 333 K and cosolvent concentration at 1.5, 3.0, 4.5 and 6.0% (by mole). The effect of pre-expansion pressure, extraction temperature, spraying distance, nozzle size and concentration of cosolvent on the precipitated particles was investigated. The results show that the mean particle size of griseofulvin precipitated by RESS was less than 1.2μm. An increase in pre-expansion pressure, extraction temperature, spraying distance and concentration of cosolvent resulted in a decrease in particle size under the operating condition studied. With the decrease of nozzle diameter the particle size reduces. The crystallinity and melting point of the original material and the processed particle by RESS were tested by X-ray diffraction (XRD) and differential scanning calorimetry (DSC).No evident modification in the crystal habit was found under the experimental conditions tested. The morphology of particles precipitated was analyzed bY scanning electron microscopy (SEM).     

超临界流体快速膨胀法制备超细微粒

超临界流体快速膨胀法（RESS）是一项近10年发展起来的制备超细微粒的新技术，它将溶解有饱和溶质的超临界流体在非常短的时间内（10^-8-10^-5s)通过一个喷嘴（25－60um)进行减压膨胀，利用强烈的机械扰动以达到极高的过饱和度（约10^6)和均相成核条件，从而产生纳米至微米级粒径且粒径及形态分布均匀的超细微粒，该方法已经在制备药物微粒，聚合物微粒和纤维，有机材料和无机材料与陶瓷先驱物等方面得到广泛的应用研究，不仅可以制备单组分的形态不同的微粒或纤维，还可以制备双组分的包覆型微粒，但理论研究目前还处于探索阶段，不能准确解释装置结构参数和操作条件对最终产物形态的影响，在此主要就超临界流体的性质，RESS方法的基本原理，理论和应用研究成果进行简单介绍。     

应用超临界流体重结晶技术制备药物微粒

总结了超细药物微粒的常规制备方法,对超临界重结晶技术的两种常用方法,即超临界流体快速膨胀法和抗溶剂法进行了介绍,阐述了它们的应用进展情况,回顾了两种方法在国内中药药材领域的研究情况。并对超临界重结晶技术进行了展望,指出该技术为我国中药材有效成分的精细制备提供了一条富有前景的道路,但需要解决制备产量低、成本高、工艺和设备尚不完善等问题。     

超临界溶液快速膨胀过程中喷嘴的流动模型

本文基于超临界流体的特性,在一维定常可压缩流动的基础上,结合对流传热建立了超临界溶液快速膨胀过程（ＲＥＳＳ）的计算模型。该模型将ＲＥＳＳ过程喷嘴内的流动分为等熵节流和一维定常可管流两个部分,利用该模型可ＲＥＳＳ过程中喷嘴内部的流动,为研究ＲＥＳＳ过程提供基础。     

RESS过程及其用于微细颗粒制备研究综述

介绍了超临界流体快速膨胀过程的主要特征，对超临界流体快速膨胀过程及用于微细颗粒制备的研究进行了综述,评析了文献对RESS过程制备微细颗粒的影响因素和对RESS过程机理模型的研究，阐述了RESS过程在不同体系下的应用研究。     

超临界流体快速膨胀技术的研究进展

超临界流体快速膨胀过程在微细颗粒制备和包覆等应用过程中具有独特的优点,是绿色化工技术。本文综述了超临界流体快速膨胀技术的原理、应用、研究现状及发展前号。     

超临界流体快速膨胀法制备微粒的研究进展

介绍了超临界流体快速膨胀法的基本原理和工艺流程及其改进和发展,着重分析和总结了最近几年RESS法及其衍生技术的研究和应用情况,并按照其超临界溶剂、溶质及喷射背景的修正对其进行归类总结。另外,还对理论研究方面的现状和近年来的一些最新进展进行了阐述,对以后的研究重点和发展方向进行了讨论。     

超临界流体快速膨胀法制备超细阿昔洛韦粒子

以二氧化碳作为超临界溶剂,采用超临界溶液快速膨胀技术制备得到超细阿昔洛韦药物粒子,在一定的温度和压力情况下,测定了阿昔洛韦在超临界二氧化碳中的溶解度,考察了各种操作参数对药物粒子粒径的影响,研究了药物粒子粒径随各种操作参数的变化规律。结果表明:阿昔洛韦在超临界二氧化碳中的溶解度较小,在10-5~10-6之间(摩尔分率),溶解度随着温度和压力的升高而增大,不存在文献中所报道的反向区。同时实验结果表明:药物粒子粒径变化对预膨胀温度最敏感,粒径随预膨胀温度的升高而减小;一定范围内随收集距离的增大而增大;在萃取温度较低的情况下,粒子粒径基本随着萃取温度的升高而减小;随着萃取温度的升高,在相对较高预膨胀温度下,粒径随着萃取温度升高而增大。     

超临界流体快速膨胀法制备超细氟比洛芬粒子

文章选用二氧化碳作为超临界溶剂,采用超临界溶液快速膨胀技术制备超细氟比洛芬药物粒子,在较宽的温度压力范围内测定了氟比洛芬在超临界二氧化碳中的溶解度,考察了各种操作参数对药物粒子粒径的影响,研究了药物粒子粒径随各种操作参数的变化规律。结果表明：在实验考察的范围内,氟比洛芬的溶解度较小,在10-5~10-7之间（摩尔分率）,溶解度随着温度和压力的升高而增大。同时实验结果表明：粒径随预膨胀压力的升高而减小;一定范围内随接收距离的增大而增大;在萃取温度较低的情况下,粒子粒径基本随着萃取温度的升高而减小;随着萃取温度的升高,在相对较高预膨胀温度下,粒径随着萃取温度升高而增大。     

超临界溶液快速膨胀法制备二氯二茂钛微粒及催化乙烯聚合

为克服茂金属催化剂得到的聚合物形态难以控制、表观密度较低、易粘釜和不适于气相淤浆聚合等缺点,以超临界溶液快速膨胀过程为手段,以期制得颗粒分布均匀的细微催化剂颗粒,继而得到形态良好的聚合物.作为超临界流体技术的基础,首先测定了二氯二茂钛在超临界丙烷中的溶解度.在此基础上,用RESS方法制得了均匀的超细催化剂颗粒,且系统考察了溶液浓度、预膨胀温度、喷嘴结构和接收距离对沉析颗粒粒径的影响.最后,将RESS所制得的催化剂颗粒进行乙烯淤浆聚合,并分析聚合物形态结构.实验结果表明,在温度为383.15～408.15 K和压力为10～35 MPa范围内,溶解度随温度的增加而增加,随压力的升高而增加,说明在该操作范围内,不存在反向区.RESS操作的结果显示,二氯二茂钛颗粒粒径随溶液浓度的增大而减小,随预膨胀温度的升高而增大,而喷嘴直径的减小和喷嘴长度的增加将使得颗粒粒径增大,而收集距离的增加将使得颗粒粒径先增加后减缓,直至不再变化.通过对原始的催化剂颗粒和RESS制得的催化剂颗粒进行乙烯淤浆聚合表征发现,相比于原始催化剂,由于烯烃催化剂的复制原理,RESS制得的催化剂颗粒的聚合物具有良好的形态.     

快速膨胀工艺制备二氧化硅超细粉的实验研究

快速膨胀工艺是利用超临界流体制备超细微粒的重要方法。本文以含二氧化硅98.3%的石英砂为原料,在超临界CO_2环境中,采用RESS工艺,在一定条件下制备了二氧化硅超细粉,并对其物理性能进行了测试,结果表明,该二氧化硅超细粉的平均粒度为0.6μm,二氧化硅的含量为99.99%。     

FORMATION OF MAGNETITE FINE PARTICLES BY CHEMICAL ABSORPTION INTO AQUEOUS SUSPENSIONS OF FERROUS HYDROXIDE

The formation of magnetite particles by oxidation of aqueous suspensions of Fe(OH)₂ with dissolved oxygen has been found to be composed of (I) the formation step of ferric hydroxo-complex by oxidation of FeOH' ion in the liquid film around the gas bubble, and (ii) the formation step of magnetite by the coprecipitation of FeOH⁺ and ferric hydroxo-complex in the thin layer adjacent to the Fe(OH)₂ particle in the bulk of suspension medium. The oxidation reaction rate can be expressed apparently by zero-order with respect to the content of total Fe(II) and by first-order with respect to the concentration of dissolved oxygen up to the fractional oxidation of 0.9.Only octahedral particles whose size ranges from O.14μm to 0.20 μmare formed so long as the oxidation reaction finishes within 50 min. When the reaction completion time becomes longer than about 90 min, almost particles are of cubic shape with a mean size of about 0.20 fim.     

FORMATION MECHANISM OF Tio2 FINE PARTICLES PREPARED BY THE SPRAY PYROLYSIS METHOD

Fine particles of Tio₂ were prepared from titanyl sulfate solution by the Spray pyrolysis Method( SPM) The reaction tube was divided into four zones: drying, dehydration, pyrolysis 1 and pyrolysis 2 zones. Under various reaction temperature and carrier gas flow rate, the mean size and the size distribution of particles collected at different sampling positions along the axial direction of the reactor were compared. The effects of operating conditions of drying, dehydration and subsequent pyrolysis steps on the formation mechanism of Tio₂ fine particles were discussed     

FORMATION MECHANISM OF Tio2 FINE PARTICLES PREPARED BY THE SPRAY PYROLYSIS METHOD

ABSTRACT

Fine particles of Tio₂ were prepared from titanyl sulfate solution by the Spray pyrolysis Method( SPM) The reaction tube was divided into four zones: drying, dehydration, pyrolysis 1 and pyrolysis 2 zones. Under various reaction temperature and carrier gas flow rate, the mean size and the size distribution of particles collected at different sampling positions along the axial direction of the reactor were compared. The effects of operating conditions of drying, dehydration and subsequent pyrolysis steps on the formation mechanism of Tio₂ fine particles were discussed     

SIZE CONTROL IN THE FORMATION OF EXTREMELY FINE GOETHITE PARTICLES BY OXIDATION OF ALKALINE SUSPENSIONS OF FERROUS HYDROXIDE

The kinetics for oxidation of an aqueous alkaline suspension of ferrous hydroxide leading to formation of fine goethite particles was reconfirmed. The mean size of the needle-like goethite particles can be correlated well to the oxidation rate. Phenomenologically, host nuclei are generated in the early stage of the reaction, and afterwards particle growth mainly occurs through hydrolysis of ferric hydroxo-complex (intermediate species) with the number of host nuclei held almost constant. The particle size can be expected to be approximately governed by the number of host nuclei generated in the early stage of the reaction and the initial concentration of total Fe(II). By shifting the oxygen concentration in the feed stream to a lower level at a low conversion, the size distribution of the prepared particles becomes narrow.     

水热系统快速膨胀法制备纳米TiO2粉体

以硫酸钛水溶液为前驱物，尿素为沉淀剂，本文采用了一种新的方法一水热系统快速膨胀法制备了纳米TiO2粉体，利用XRD、TEM等测试手段研究了硫酸钛浓度、尿素浓度、膨胀前温度对粉体粒径的影响。结果表明：所制得粉体为锐钛矿型TiO2晶体，粒径为10纳米左右，并且分散良好。     

分散剂在醇-水溶液加热法制备球形 ZrO2粉体过程中的作用

本工作对分散剂在醇－水溶液加热法制备球形ZrO2粉体过程中的作用进行了研究。研究结果表明：在异丙醇－水溶液加热法制备球形ZrO2粉体时,聚合物分散剂起着明显的作用。当无分散剂加入时,所得ZrO2颗粒无规则且团聚严重;而当溶液中加入PEI（polyethyleneimine)时,可获得球形ZrO2颗粒,与加入PEI相比,加入NH4PAA或PEG所得ZrO2颗粒形状不够完整且团聚较多,这一区别可由聚合物分散剂在ZrO2颗粒上的吸附情况的不同得到初步解释。     

炉内温度对聚碳硅烷粒子成球性能的影响

由聚碳硅烷粒子作为原料,通过粒子下落进入负压高温炉内,粒子达到流动状态,在发泡剂作用下内部起泡膨胀,最终得到空心微球.实验所用聚碳硅烷粒子尺寸为110～180 μm,载气为Ar/He（体积比为2：1）,载气压力为0.09MPa.在这些固定条件下,研究了炉内温度对聚碳硅烷粒子成球性能的影响.结果表明：随着炉内温度从200℃升高到1 000℃,聚碳硅烷成球率、微球平均直径和表面光洁度先增加后下降,最高平均成球率为73%,最大平均直径为375μm,最好表面平均粗糙度Ra仅为0.7 nm.制备空心微球合适的温度约为700℃.     

INHIBITION OF MASS TRANSFER TO POROUS ADSORBENTS BY FINE PARTICLES AND ORGANICS

Activated carbon and ion-exchange resins are used industrially for the extraction of metal cyanides from slurries. This paper attempts to quantify the inhibition of mass transfer to these adsorbents owing to fouling by fine particles and organics usually present in leached pulps. In this study, resins and carbon were contacted with either solutions of organics, or dilute slurries of synthetic silica or alumina in batch stirred tanks. Silver cyanide was used as an adsorbate to detect changes in the mass transfer characteristics of the adsorbents, which were ashed to determine the loading of silica or alumina. The rate of intrusion of fine particles into the adsorbent matrix was relatively fast, and was dependent on the concentration of particles in the slurry. SEM mappings of Si and Al showed that the intruded particles were distributed fairly homogeneously throughout the adsorbent particles. It was found that the presence of fine inert particles and organics had no effect on the equilibrium loading of silver cyanide on either the resin or carbon. The reduction in the rate of adsorption appeared to be a kinetic influence, and could be attributed to two effects, viz.: (1) pore blocking, and therefore retarded diffusion into the resin bead or carbon granule, and (2) temporary blinding of the resin or carbon surface. By fitting a film transport-surface diffusion model to the profiles for the uptake of silver cyanide, it was found that a decrease in the intraparticle diffusivity was associated with pore blocking.