通过本章学习应掌握的内容

1、第二讲过滤2学时一、通过本章学习应掌握的内容1、何谓过滤2、过滤的基本形式3、凝聚和絮凝的区别4、常用的絮凝剂有哪些5、过滤设备分类6、常用过滤设备及其特点二、过滤的基本概念过滤是在某一支撑物上放过滤介质，注入含固体颗粒的溶液，使液体通过，固体颗粒留下，是固液分离的常用方法之一。Filtration separates solid from a liquid by forcing the liquid through a solid support or filter medium. This is a straight forward procedure for well defined c

2、rystals. 三、过滤前物料的前处理However the small size of microorganisms make filtration of fermentation beers or other biological solutions considerably more complicated. Generally, fermentation beers and other biological solutions are notoriously hard to filter. They are often hard to filter because of high n

3、on-Newtonian viscosity or highly compressible cakes. That is to say, we must modified these procedures for bio-separations.通常发酵液和生物溶液是高粘度的和非牛顿流体，是很难过滤的，为了加快过滤速度，通常可采用以下方法：1、加热（Heating）降低液体粘度2、凝聚和絮凝（Coagulation and flocculation）在电介质作用下，破坏溶质胶体颗粒表面的双电层，破坏胶体系统的分散状态，使胶体粒子聚集的过程四、影响凝聚作用的主要因素Simple electrol

4、ytes act by screening the electrostatic repulsion, which commonly exists between colloidal particles. When this electrostatic repulsion is reduced, attractive London-vander waals forces predominate. The colloids can then coagulate as larger, dense particles which are more easily filtered. (简单电解质降低胶体

5、间的排斥力。从而范德华引力起主导作用，聚合成较大的胶粒，粒子的密度越大，越易分离。)1、无机盐的种类2、无机盐的化合价3、无机盐的用量常用的凝聚剂有：Al2(SO4)3.18(H2O)，AlCl3.6(H2O)，FeCl3，ZnSO4，MgCO3五、絮凝作用(Flocculation)概念：指在某些高分子絮凝剂存在下，在悬浮粒子之间发生架桥作用而使胶粒形成粗大的絮凝团的过程Synthetic polyelectrolytes added as pretreatments can both reduce electrostatic repulsion and adsorb on adjacent

6、 particles, forming bridges between them. As a result, the colloidal particles flocculate as large, less dense aggregates which are more easily filtered. These polyelectrolytes can be anionic, cationic or nonionic.（合成助滤剂既降低静电斥力又吸附周围的微粒，形成桥架作用。胶粒过大，就发生絮凝，低密度聚合的胶粒，容易过滤。聚合电解质有阳离子型、阴离子型或非离子型。六、常用的絮凝剂1、天

7、然聚合物多糖类物质、海藻酸钠、明胶等2、人工合成聚合物聚丙烯酰胺类衍生物、聚苯乙烯类衍生物、聚丙烯酸类等七、助滤剂1、目的：助滤剂是一种具有特殊性能的细粉或纤维，它能使某些难以过滤的物料变得容易过滤2、常用的助滤剂：硅藻土（Diatomaceous earths）珍珠岩（Perlites）八、General Theory for FiltrationFluid mechanics for filtration Darcys law （Darcy方程）for incompressible cake, simplest case（适用于不可压缩和简单的可压缩滤饼）for compressible

8、cake, common for bio-separations（普遍使用于生物分离过程。）1、Darcys law（达西定律）V=k P/l (2.1)where Vvelocity of the liquid kproportionality constant (usually called the Darcys law permeability of the bed) （K比例常数,过滤床渗透性的达西方程参数）Pthe pressure drop across the bed of thickness （压降） viscosity of the liquid （流体粘度）*当Re5时达西

9、定律才成立For batch filtration the velocity is（板框式过滤流速方程） V=(1/A)*dV/dt (2.2)Afiltration area （过滤面积）Vthe total volume of filtration（滤液总体积）tthe filtration time（过滤时间）有l/k= Rm + Rc （2.3）Rmthe resistance of the filter medium RM （过滤介质的阻力）Rcthe resistance of accumulate cake bio-mass （滤饼的阻力）2、Incompressible Cak

10、es（不可压缩滤饼）If the cake is in compressible (rigid), the cake thickness is directly proportional to the filter area. （不可压缩滤饼厚度正比于过滤的体积） As a result the cakes resistance Rc is Rc=o(V/A) (2.4)where represents the specific cake resistance （滤饼的阻力特性）othe mass of cake solids per volume of filtrate （单位体积滤液含固体

11、滤饼量）3、Compressible cake（可压缩的滤饼）Almost all cakes formed of biological materials are compressible, and so cannot be described with the simple equation just outlined. As these cakes compress, filtration rates drop. （大多数生物滤饼都可压缩，不能仅用作图法描述，滤饼可压缩，则过滤速度降低）=(P)sWherea constant related largely to the size &

12、shape of the particles forming the cake.（与粒子大小和形状相关）S the cake compressibility （s是压缩系数）S=0 a rigid & highly incompressible cake （理想的不可压缩s=0）S=1 a highly compressible cake （高度可压缩 s=1）S=0.1-0.8 in practice （变化范围从0到1）Values of S & are most easily determined by plotting the logarithm of versus the logar

13、ithm of P as shown in fig.(2.1)（计算s和可用log对logP作图）九、Continuous Rotary Filter 连续旋转式过滤机We analyze the operation of these units, a filtration cycle on this filter consists of three chief （过滤有三步组成）1、cake formation（滤饼的形成）2、cake washing to remove either or unwanted solutes（滤饼的洗涤）3、cake discharge（滤饼的卸下）we a

14、ssume that the resistance of the filter medium Rm is negligible, so that we can use equation (2.5)（假设滤饼阻力不计），the basic expression for filtration(1/A)*dV/dt = P/( Rc)initial condition that（初始条件是）t=0 v=0 Rc = o (V/A) =o(V/A)( P)s tf=(o/(2P1-s)*(Vf/A) tf the cake formation time （滤饼形成时间）Vfthe volume of

15、filtrate collected during that period.（滤液流量）*cake washing（滤饼的洗涤）作用：（1）First, it displays the solution-rich broth trapped in pores in the cake.（将滤饼内发酵液洗出）（2）Second, it allows diffusion of solute out of the biomass in the cake. Such diffusion will enhance recovery, if the desired product is in the biomass.（扩散出生物有机体，这对目标产物在生物有机体很有用）八、过滤设备及其结构过滤设备的分类根据推动力的不同可分为四类（a）重力过滤自然过滤（b）加压过滤板框过滤（c）