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1、Chapter 2 Filtration 第二章 过 滤,1,大家好,Key knowledge points(知识点),A Pretreatment 预处理1、Heating 加热2、Coagulation and flocculation 凝聚和絮凝3、Adsorption on filter aids 助滤剂上的吸附B General Theory for Filtration1、Darcys Law 达西方程 2、Incompressible Cakes 不可压缩滤饼t(o/(2P)*(V/A)23、Compressible cake 可压缩的滤饼C Continuous Rotary
2、 Filter连续旋转式过滤机D Equipment for Conventional Filtration 传统的过滤设备,2,大家好,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。,3,大家好,滤饼,传
3、统的过滤,cake,Conventional filtration,大家好,under,大家好,大家好,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。,7,大家好,Generally,fermentation beers and other biological solutions are no
4、toriously hard to filter.They are often hard to filter because of high non-Newtonian viscosity or highly compressible cakes.That is to say,we must modify these procedures for bio-separations.一般，由于料液通常都是高的非牛顿粘度流体或者是高度可压缩滤饼，发酵液和其它生物溶液是极其难以过滤的，也就是说，我们必须对这些生物分离程序进行修改。,8,大家好,A Pretreatment 预处理,1、Heating
5、加热2、Coagulation and flocculation 凝聚和絮凝3、Adsorption on filter aids 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。,9,大家好,1、Heating 加热,The simplest pretreatment and the least expensive method is to heat the feed.Such heating can not only improve the fee
6、ds 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。,10,大家好,2、Coagulation and flocculation 凝聚和絮凝,The second pretreatment me
7、thod 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。,11,大家好,Simple electrolytes act by screening the
8、 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
9、粒，粒子的密度越大，越易分离。,12,大家好,18,pH 3.8,pH 2.8,The effect on filtrate volume of pH,pH值对过滤体积的影响,大家好,Time(min),18,The effect on filtrate volume of filter aid,助滤剂对过滤体积的影响,大家好,Simple acids and bases（简单的酸或碱）Alum（明矾）Ferric chloride crystals（三氯化铁）,15,大家好,Synthetic polyelectrolytes added as pretreatments can both
10、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，
11、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。,Polyacrylamides（聚丙烯酰胺）Polyethylenimines（聚乙烯亚胺）Polyamine derivatives（多聚胺衍生物）,16,大家好,（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。（2）、Perlites 珍珠岩 The perlites are volcanic
12、 rock processed to yield an expanded form.珍珠岩是处理过的膨胀火山岩。,3、Adsorption on Filter Aids 助滤剂上的吸附,17,大家好,Table 2.1.Typical properties of Filter Aids,18,大家好,B.General Theory for Filtration,Now we turn to the mathematical description of filtration.现在我们对过滤过程进行数学描述。,19,大家好,Darcy方程fluid mechanics for filtrati
13、on Darcys law：1、for incompressible cake,simplest case 适用于不可压缩和简单的可压缩滤饼 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,20,大家好,Darcys law（达西定律）,Darcys law relates the flow rate through a porous bed of solids to the pressure drop causing that flow Darcy定律把流速与通过固体多孔床产生的压降联系起来。v=
14、kP/l(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,21,大家好,v is the velocity of the liquid v 流体流速k：proportionality constant,usually called the Darcys 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:viscosi
15、ty of the liquid 液体粘度,22,大家好,Darcys law holds only when Re5 当Re5时达西定律才成立 Re=dv/(1-)(2.2)d-particle size or pore diameter in the filter cake 滤饼粒子的大小或孔的直径-the void fraction in the cake 滤饼空隙率-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,23,大家好,For batch filtrati
16、on,the velocity is对于板框式过滤,速率方程为：v=(1/A)*dV/dt(2.3)A filtration area 过滤面积V the total volume of filtration 过滤液体积t the filtration time 过滤时间,24,大家好,The resistance to include explicitly the contributions of cake and filter medium.滤饼和过滤介质所产生的阻力：l/k=Rm+Rc(2.4）Rm the resistance of the filter medium 过滤介质的阻力R
17、c the resistance of accumulate cake bio-mass 滤饼的阻力,25,大家好,Combining E.q.(2.1)(2.3)(2.4)we find differential equation for batch filtration at the constant pressure drop：我们发现板筐式过滤压降是一个常数(1/A)*dV/dt=P/(Rm+Rc)(2.5)Rm is a constant independent of the cake；Rm是常数，与滤饼无关；RC the cakes resistance varies with t
18、otal volume of filtration；Rc与滤液总体积有关；The exact nature of this variation depends on whether the cake is incompressible or not.Rc的变化取决于滤饼是不可压缩还是可压缩。,26,大家好,If the cake is in compressible(rigid),the cake thickness is directly proportional filtrate volume and inversely proportional to the filter area.如果
19、滤饼是不可压缩的，则滤饼的厚度正比于过滤液的体积，反比于过滤面积。,1、Incompressible Cakes 不可压缩滤饼,27,大家好,As a result the cakes resistance Rc is 滤饼的阻力Rc可以用（2.6）来描述 Rc=o(V/A)(2.6)-represents the specific cake resistance 滤饼的阻力特性o-the mass of cake solids per volume of filtrate 单位体积滤液含固体滤饼量,28,大家好,Substituted of(2.6)into(2.5).Differentia
20、l equation for incompressible cake is:把方程（2.6）代入（2.5）得到：(1/A)*dV/dt=P/(o(V/A)+Rm)(2.7)The equation is subject to the initial condition 初始条件为：T=0 V=0(2.8)This condition says that at the start of the experiment,no solution has been filtered.开始时没有滤液被过滤,29,大家好,(2.7)integrated and rearranged to give（2.7）
21、积分后整理得(At/V)=K(V/A)+B(2.9)K=o/(2P)(2.10)B=Rm/P(2.11)thus the plot of(At/V)versus(V/A)should be linear.用At/V对 V/A作图应该是线性的。K-the slope is a function of the pressure drop and of the properties of the cake；斜率K是压降P及滤饼特性、o的函数B-the Intercept is independent of the properties of the cake,but it is proportion
22、al to the mediums resistance,usually Rm is insignificant.截距B与滤饼特性无关，但它正比于介质阻力Rm。通常Rm可忽略不计,30,大家好,Eq.(2.9)becomes simple方程（2.9）可简化为：t(o/(2P)*(V/A)2(2.12)These equations are valid for incompressible cakes.（该式仅适合不可压缩的滤饼）,31,大家好,2、Compressible cake 可压缩的滤饼,Almost all cakes formed of biological materials
23、are compressible,and so cannot be described with the simple equation just outlined.As these cakes compress,filtration rates drop.This in turn results in compromised economics.绝大多数生物滤饼都可压缩，因此，不能仅仅用作图法的简单方法来描述，滤饼可压缩，则过滤速度降低，能耗增大。,32,大家好,To estimate the effects of compressibility,we assume that the cak
24、e resistance is a function of the pressure drop.为了估计可压缩性的影响，我们假设滤饼阻力是压降的函数。=(P)s(2.13)-a constant related largely to the size&shape of the particles,forming the cake.是一个与滤饼组成、粒子大小和形状相关的常数sthe cake compressibility 滤饼的压缩系数 s=0 a rigid&highly incompressible cake 理想的不可压缩滤饼 s=1 a highly compressible cake
25、 s=1 高度可压缩滤饼 s=0.1-0.8 in practice（实践中，s的变化范围是0.1-0.8）,33,大家好,Values of s are high,we should consider pretreating the feed with filter aids.当s的数值很高时，须加入助滤剂对原液进行预处理。,Values of s&are most easily determined by plotting the logarithm of versus the logarithm of P as shown in fig.(2.2).为计算出s和，可用log对logP作图
26、，如图2.2：,log P,log,Fig Cake resistance versus pressure drop,34,大家好,C、Continuous Rotary Filter 连续旋转式过滤机,A filtration cycle on this filter consists of three chiefs.一个完整的过滤过程主要为三个步骤a.cake formation 滤饼的形成b.cake washing to remove either valuable or unwanted solutes.洗涤滤饼以除去有用或不需要的溶质c.cake discharge 滤饼的清除,3
27、5,大家好,Dry,Wash,Immersion,Rotation,Knife,Cake,Feed,Rotary vacuum filter,真空旋转过滤机,大家好,we first consider the cake formation which begins as the rotating drum first drops into the broth.滤饼形成是从转鼓一开始接触培养基开始的we assume that the resistance of the filter medium Rm is negligible,so that we can use equation(2.5)
28、the basic expression for filtration.假设过滤介质的阻力Rm可忽略不计，式（2.5）可以用下式表示：(1/A)*dV/dt=P/(Rc)(3.1)initial condition that is 初始条件是 t=0 v=0(3.2),37,大家好,We rewrite Rc for a compressible cake by combining(2.6)&(2.13)结合方程（2.6）和（2.13）可以改写滤饼阻力Rc为：Rc=o(V/A)=o(V/A)(P)s(3.3)tf=(o/(2P1-s)*(Vf/A)2(3.4)tf-the cake forma
29、tion time 滤饼形成时间 Vf-the volume of filtrate collected during that period.滤饼形成期间被集中的滤液体积（滤液流量）,38,大家好,This relationship is sometimes written in terms of the cycle time:这个关系有时也可用旋转周期tc来表示：tf=tc（3.5）the fraction of time that the filter is submerged.That is the fraction of the cycle devoted to cake forma
30、tion 过滤器被浸渍的时间分数，即旋转周期形成滤饼所用的时间分数tc-the cycle time 旋转周期,39,大家好,We find a relation for filtration flux expressed in terms of cycle time:用旋转周期表示为：Vf/(Atc)=(2(P1-s)/(o tc)0.5（3.6）,40,大家好,1、cake washing（滤饼的洗涤）,After formation,the cake contains a significant amount of solute-rich liquid broth.This broth
31、is usually removed by washing the cake.滤饼形成以后，滤饼中还含有许多溶质需要进一步洗涤。,41,大家好,The washing has two functions：洗涤有两个作用：,First,it displays the solution-rich broth trapped in pores in the cake.将孔中含有的发酵液洗出；Second,it allows diffusion of solute out of the biomass in the cake.Such diffusion will enhance recovery,i
32、f the desired product is in the biomass.滤饼中，溶质可以从生物机体中扩散出，如果目标产物存在于生物机体中，这种扩散可以提高回收。,42,大家好,Two factors are involved in the washing：两个因素:,The first is that fraction of soluble material remaining after the wash,this governs the volume of wash liquid required.一是洗涤之后残留在滤饼中的可溶物质的部分，这个部分决定着所需洗液的体积The rat
33、e at which wash liquid passed through the cakethis rate of wash controls the time of the cycle devoted to washing.洗液通过过滤饼速率，这个速率控制着时间,43,大家好,The function of soluble material remaining is often related to the volumes of wash liquid by the equation.残留可溶物的分数常与洗液体积有关 r=(1-)n(3.7)r-the ratio of solubles
34、remaining after the wash to that originally present in the cake prior to the wash.r为洗涤之后的滤饼中溶质含量与洗涤之前滤饼中最初溶质含量比。n-the volume of wash liquid divided by the volume of the liquid retained in the cake.洗液的体积与滤饼中残液的体积之比-washing efficiency of the cake 滤饼的洗涤效率the fraction r varies from 01.lower values of r
35、correspond to more effective washing.r值越低，洗涤效果越好 if=0 r=1 we get no reduction of solubles.no matter what volume of wash is used.如果=0 r=1，此时不论使用多少洗液均没有效果 if r=0=1 more effective washing.洗涤效果很好 Equation(3.7)is an empirical result from a variety of filtrations.式3.7是大量实践得到的经验方程式,44,大家好,We may wonder how
36、 well such an empiricism works for bioseparations.我们会思考该方程对于生物分离的准确性One test of the empiricism is given in Fig on next slide for a beer containing the antibiotic in a cake of bacteria.The figure is a plot of the logarithm of r versus n,the straight lines on this plot,for efficiencies,have slopes of
37、log(1-).滤饼中包含抗生素的发酵液的过滤，图由logr对应n组成，对于不同效率，有不同的斜率log（1-）log r=nlog(1-)log rn slope=log(1-),45,大家好,pH 5.0,pH 9.3,0,0.02,0.04,0.10,0.20,0.40,0.60,1.00,1.0,2.0,3.0,0.90,0.80,0.60,0.40,0.20,WASH LIQUID/RETAINED LIQUID n,RETAINED SOLUTES/ORIGINAL SOLUTES r,Efficiency of washing,洗涤效率,大家好,Data for measurem
38、ents at two values of pH show that efficiency does vary with pH.两个不同pH值下的测量数据说明效率随着pH变化而变化The scatter of these data is typical and illustrates the accuracy of the empirical Fig(3.7).这些数据的离散度是典型的，很好的表示了经验式3.7的准确性。Thus we can estimate how much wash liquid will be needed to wash the cake.我们可以估计洗涤滤饼所需要洗
39、涤液的用量。,47,大家好,We now turn to how fast this liquid will flow though the cake,which is the second key factors.现在我们开始讨论另一个因素:流过滤饼的流速。The wash liquid contains no additional solids,so the flow of wash liquid will be constant and equal to the final instantaneous filtrate rate at the end of the cake format
40、ion.This rate is 洗液不包含所加的固体物，因此，洗液的流量是一个常量，且等于滤饼形成的最后瞬间过滤液的速率，这个速率是：vw/A=2(p)1-s/01/2(tw)1/2(3.8）vw-the volume of wash water required 所需的洗液体积 tw-the time required for washing 洗涤时间,48,大家好,In many cases,we may find it useful to divide this result by eq(3.9),to obtain:许多情况下，通过式3.9得到的结果是十分有用的 tw/tf=2 vw
41、/vf(3.9)=2(vw/vr)(vr/vf)=2nf(3.10)Vrthe volume of liquid retained by the cake 滤饼中残液的体积 fthe ratio of this volume to the volume of filtrate 体积Vr占总滤液体积的分数,49,大家好,Equipment for filtration various widely,from the conventional plat-and-frame press to rotary vacuum filters.过滤设备从传统的板框式过滤机到旋转式真空过滤设备，种类很多。,D
42、、Equipment for Conventional Filtration 传统的过滤设备,50,大家好,51,大家好,52,大家好,The most common,the plate-and-frame press,contains caulked,metal septa and a recessed cake space.最普遍的是板框式过滤机，有可填充的、金属隔片的和凹显空间滤饼的。Other types have flushed plates that can be used with a paper or cloth filter medium separated by open
43、frames where the cake is formed.This type of filter is used where a relatively dry cake discharged is desired.It should not be used where there are toxic fumes or biohazards.其它类型还有平的金属板，可用滤纸或滤布过滤介质在开放式框架上分离形成滤饼。这种过滤机适合于相对的干性滤饼，能被清除，不适合有毒气和生物危害物的滤饼。,53,大家好,The other three filters are enclosed and hen
44、ce can be used with aerosols or biohazards.Because their use is labor intensive,they are used on for relatively small scale work.其它三种过滤机是封闭型的，可过滤悬浮颗粒和有生物危害物质，一般用于小规模生产。,54,大家好,思考题：1.发酵液进行过滤的目的是什么？影响发酵液过滤速度的因素有哪些？2.发酵液过滤的方法有哪些？并简述各种方法的类型、特点及应用。3.如何进行过滤介质的选择和过滤条件的优化？4.发酵液过滤所用的过滤机类型有哪些？并简述各种过滤机的结构、特点和应用。5.提高过滤压力和增大过滤面积是否为强化过滤的最有效措施?6.针对不可压缩和可压缩滤饼进行过滤时间的公式推导以及可能的应用计算,55,大家好,结束,56,大家好,
