（2）、Perlites 珍珠岩
The perlites are volcanic rock processed to yield an expanded form. 珍珠岩是处理过的膨胀火山岩。
Table 2.1. Typical properties of Filter Aids
B. General Theory for Filtration
Filtration separates solid from a liquid by forcing the liquid through a solid support or filter medium. This is a straightforward procedure for well defined crystals. 过滤是将料液通过固体支持或者过滤介质时，使得固 体物质从溶液中分离，对于好的定形的晶体，这是一 种最直接的步骤。
Darcy定律把流速与通过固体多孔床产生的压降联系起来。
v=k△P/μl
(2.1)
v directly proportional to △P
流速正比于压降
v inversely proportional to l/k
流速反比于阻力l/k
v is the velocity of the liquid v – 流体流速 k ： proportionality constant, usually called the Darcy’s law permeability of the bed k－比例常数,通常叫达西方程参数 △P: the pressure drop across the bed of thickness △P－通过厚度为l的床产生的压降 μ: viscosity of the liquid μ－液体粘度
Synthetic polyelectrolytes added as pretreatments can both reduce electrostatic repulsion and adsorb on adjacent 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. 预处理时加入合成聚合电解质既能降低排斥电位，又吸附了周围的微 粒，形成桥架作用，促使胶粒形成粗大，密度低的絮凝团。这些絮 凝团很容易被过滤得到。
pH 2.8
Filtrate Volume (cm3)
pH 3.8 600
pH 4.2 400
200
pH 4.6
0
0
6
12
18
Time (min)
The effect on filtrate volume of pH
pH值对过滤体积的影响
Filtrate Volume (cm3)
5% 3% 2%
However the small size of microorganisms make filtration of fermentation beers or other biological solutions considerably more complicated. 但对微小而形状多变的微生物细胞，发酵液和其它生 物溶液的过滤就变得复杂了 。
F lo w s h e e t fo r c o n tin u o u s ro ta ry v a c u u m filtra tio n
w a sh sp ra ys
A ir c o n n e c tio n C o n tin u o s ro ta ry filte r
M o is tu re tra p
· Darcy’s law holds only when Re<5
当Re<5时达西定律才成立 Re= dvρ/μ(1-ε)
d-particle size or pore diameter in the filter cake 滤饼粒子的大小或孔的直径
ε-the void fraction in the cake 滤饼空隙率 ρ-the liquid density 液体的密度 v is the velocity of the liquid 流体流速 Re – Reynolds number 雷诺准数
Polyacrylamides（聚丙烯酰胺）
Polyethylenimines（聚乙烯亚胺）
Polyamine derivatives（多聚胺衍生物）
3、Adsorption on Filter Aids 助滤剂上的吸附
（1）、Diatomaceous earths 硅藻土
Diatomaceous earths are the skeletal remains of the tiny aquatic plants deposited centuries ago. 硅藻土是百年前水生植物沉淀下来的遗骸。
1、Darcy’s Law 达西方程 2、Incompressible Cakes 不可压缩滤饼
t＝(μαρo/(2△P))*(V/A)2 3、 Compressible cake 可压缩的滤饼
C Continuous Rotary Filter连续旋转式过滤机
D Equipment for Conventional Filtration 传统的 过滤设备
cake
W ash w a te r pum p
30'
W ash
V acuum re c e iv e rs
F iltra te
D ry vacuum pum p
A ir out
pum p
B a ro m e tric seal
F ig u re 2 .2 F lo w s h e e t fo r c o n tin u o u s ro ta ry v a c u u m filtra tio n
Now we turn to the mathematical description of filtration.
现在我们对过滤过程进行数学描述 。
Darcy方程－－fluid mechanics for filtration Darcy’s law ：
1、for incompressible cake, simplest case 适用于不可压缩和简单的可压缩滤饼
1、 Heating 加热
The simplest pretreatment and the least expensive method is to heat the feed. Such heating can not only improve the feed’s handling characteristics, but also may pasteurize it. The chief constraint of this approach is the thermal stability of the product. (lead to irreversible reaction). 最简单、最经济的预处理方法是加热，加热不仅可以增加 料液的操作特性，也可以对其进行灭菌。但加热变性的方 法只适合于对热稳定性的产物。
cake 滤饼
传统的过滤
Conventional filtration
filter filter filter
Conceptual representation of plate and frame filter filtrate
solids recovery upon backflush Figure2.1 Schematic respresentation ounddesr filter press
2、Coagulation and flocculation 凝聚和絮凝
The second pretreatment method is the addition of electrolytes to promote coagulation and flocculation in the initial solution. Useful agents rang from simple electrolytes through acids and bases to synthetic polyelectrolytes. 第二种预处理方法是通过电解质的加入促进原始溶液的 凝聚和絮凝，试剂有简单的电解质、酸、碱、合成的聚 合电解质。
2、for compressible cake, common for bio-separations 适用于可压缩滤饼，普遍使用于生物分离过程
Darcy’s law （达西定律）
Darcy’s law relates the flow rate through a porous bed of solids to the pressure drop causing that flow
A Pretreatment 预处理
1、Heating 加热 2、Coagulation and flocculation 3、Adsorption on filter aids
凝聚和絮凝 助滤剂上的吸附
These treatments are also useful for
centrifugation and sedimentation. 这些方法也适用于对于离心和沉淀过程。
Simple electrolytes 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. 简单电解质降低了胶体粒子间的排斥电位，从而使得范德华引力起 主导作用，聚合成较大的胶粒，粒子的密度越大，越易分离。