气体吸收——相际扩散与传质原理（双语版）_第8章 气体吸收 §8.2气液相平衡

88.2 Equilibrium between liquid and gas 8.2.ISolubility at equilibrium c(1) limitation of 一~平衡溶解度 gas a bsorption The solubility of gas in the liquid At T and P, s+ mixture of gases of A+B, intimate contact。随着两者的不断接触, solute a from gas phase→ transfer to liquid phase,unti液相 中 solute达到un- saturation It is dynamic balance at the moment which concentrations of a are constant within&v. that is the amount of molecules of A entering in L phase the amount of molecules of A escaping from L phase

一.The solubility of gas in the liquid At T and P, S + mixture of gases of A+B, intimate contact 。随着两者的不断接触，solute A from gas phase →transfer to liquid phase, until液相 中solute达到un-saturation。 It is dynamic balance at the moment which concentrations of A are constant within L &V, that is, the amount of molecules of A entering in L phase = the amount of molecules of A escaping from L phase. 8.2.1Solubility at equilibrium 平衡溶解度 §8.2 Equilibrium between liquid and gas ～ ⑴ limitation of gas absorption

821 Solubility at equilibrium~平衡溶解度 从宏观上看,吸收过程终止,即气液两相达 到相平衡。显然,此时A在液相中的浓度最大。 此浓度称为饱和浓度,或溶质A的溶解度CA※ Definition solubility: * A Kg A or A kg Solution M Solution

从宏观上看，吸收过程终止，即气液两相达 到相平衡。显然，此时A在液相中的浓度最大。 此浓度称为饱和浓度，或溶质A的溶解度CA ※ . ∴ Definition solubility: 8.2.1Solubility at equilibrium ～平衡溶解度 3 * kg A = or kg A kg Soluti A on M Solution C            

8,2. I Solubility at equilibrium~平衡溶解度 1. Solubility curve~溶解度曲线 Assume: that only one component is transferred between phases According to the phase rule of F=c-p+2,p=2 and there are three components c=3 F=3-2+2=3 There are four variables: Pressure, Temperature, and the concentrations of component A in liquid and gas. The temperature and pressure may be fixed. One concentration may be chosen as the remaining independent variable. The other concentration is then determined

1. Solubility curve ～溶解度曲线 Assume: that only one component is transferred between phases . According to the phase rule of F= c – p + 2, p=2 and there are three components, c=3. F = 3 – 2 + 2 = 3 There are four variables: Pressure, Temperature, and the concentrations of component A in liquid and gas. The temperature and pressure may be fixed. One concentration may be chosen as the remaining independent variable. The other concentration is then determined. 8.2.1Solubility at equilibrium ～平衡溶解度

82.1S0 ibility at equilibrium~平衡溶解度 溶解度曲线的3种表示方式,即3 种气~液平衡相图简称相图)。 t=293K 101.3kPa 60℃ 0 0.4 355N CPA=1. 38cA 0.3 0 0.1 图9-3293K下几种气体在水中的溶解度曲线cA 图中横坐标10°cA中的n值如下 气 体 COz 液相中氨的摩尔分数x 0.0020.0040.0060.0080.010.0120.014 液相中SO2摩尔分数x 例:气相溶质的分压p=20kPa时,水中溶质的平衡浓度 图8-3氨在水中的平衡溶解度 对CO2为102c·(CO2)=0.78,故c(CO2)=0.0078 图8-4101.3kPa下SO2在水中的溶解度 kmol/m3,对SO2为10c·(SO2)=3.37,故c(SO2)= 0.337 kmol/m

8.2.1Solubility at equilibrium ～平衡溶解度 溶解度曲线的3种表示方式，即3 种气～液平衡相图(简称相图)

82.1 Solubility at equilibrium~平衡溶解度 For example Fig 8-4, p=1013kpa, t=40C, all points of(ye,xe) on the curve pertain to(关于) the same temperature and pressure. 2 Factors affecting on solubility According to the phase rule. F=3 In the four variables of T, P, pa and cA, there are three independent variables only where: pa partial pressure of A in gas phase. CA =f(T,P,pA

For example Fig .8-4， p=101.3kpa，t=40℃, all points of (ye , xe ) on the curve pertain to (关于）the same temperature and pressure. 2 Factors affecting on solubility ∵ According to the phase rule, F =3 ∴ In the four variables of T, P, pA and cA, there are three independent variables only. where: pA ～ partial pressure of A in gas phase. 8.2.1Solubility at equilibrium ～平衡溶解度 ( A ) * C = f T, P,p A

82 Solubility at equilibriun~平衡溶解度 (1) Affection of temperature 分析相图Fig8-3, 100 For example: at pa=20 kPa 60℃ T=30℃,xAx=0.12; 50℃ T=60℃,xA*=0.045 兰感 40℃ X A 温度愈低,愈有利于吸收。20 But,在实际吸收操作时,已选 0.050 0.150.2 择确定了某一合适的吸收温度。 液相中氨的摩尔分数x 图8-3氨在水中的平衡溶解度 A PA

⑴ Affection of temperature 分析相图Fig. 8-3， For example: at pA= 20 kPa， T=30℃, xA*= 0.12； T=60℃, xA*= 0.045. T↑→ xA *↓ 温度愈低，愈有利于吸收。 But，在实际吸收操作时，已选 择确定了某一合适的吸收温度。 ∴ 8.2.1Solubility at equilibrium ～平衡溶解度 ( ) * A A x f P,p =

8.2. ISolubility at equilibrium~平衡溶解度 (2)Affection of pressure 实验证明 When p is less than5atm,o the affection may be neglected by 60℃ pressure on the equilibria for system. Commonly the pressure in3 602 50t the system of absorption operation 40 <5 atm. Then xA=f(pA) or pA= f(xA)如Fig.8-3,atT=30℃, 0.050 0.150.2 pa=20 kPa, XA=0.12 液相中氨的摩尔分数x pa=40 KPa, XA =0.19. 图8-3氨在水中的平衡溶解度 即:pA愈高,愈有利于吸收

⑵Affection of pressure 实验证明:When P is less than 5 atm, the affection may be neglected by pressure on the equilibria for system. Commonly the pressure in the system of absorption operation < 5 atm. Then xA* = f (pA) or pA*= f (xA) 如 Fig. 8-3，at T=30℃, pA=20 kPa, xA*= 0.12； pA=40 kPa, xA*= 0.19. 即：pA愈高，愈有利于吸收。 8.2.1Solubility at equilibrium ～平衡溶解度

8.2, L Solubility at equilibrium~平衡溶解度 (3)因气液平衡理论研究尚不完善,气液相平衡数据一般 都是对特定物系进行实验测定的。 测定的结果或用相图表示,或用表格表示。 二、几种气体溶于水时的亨利系数 温度/C 气体 05101520253035404550607080 E×10-3/MPa H2|5.8716166416.706.9217.167.387.527.617.707.757.75717.6526i N2|5.366.056.77|7.488.14|8.769.369.9810.511.011412.212.712.812.8 空气|4.384.945.566.156737.297.818348819.239.5810.210.610.8110.9 CO|3574.014.484.955.43|5.87|6.28|6.687.057.387.718.328.568568.57 22.582953313.694.064.44|4.815.14|5.425.705.966.376.72|6.967.08 CH42.272.623.013.413.814.18|4.5514.925.275.58|5.856.346.756.917.01 No|1.71.961.962.452.67|2.913.143353.57|377|3954.234.344.544.5 C2H1.271.911.57|2.90|2.663.063.473.88|4.284.69|5075.72|6.316.706.9

⑶ 因气液平衡理论研究尚不完善，气液相平衡数据一般 都是对特定物系进行实验测定的。 测定的结果或用相图表示，或用表格表示。 8.2.1Solubility at equilibrium ～平衡溶解度

8.2. Solubility at equilibrium~平衡溶解度 在进行具体计算时,需要相关的平衡数据。若手算,人 工查图或查表;若机算,则可将图或表上的相关数据 进行经验回归,得到经验回归方程xA*=f(pA)or pA*=f(xA)提供于计算机使用。 (4)Conclusions: a系统压力不太高时的等温吸收,可认为气体在液体 中的溶解度只取决于该气体的分压 b吸收操作的适宜条件:低温高压

在进行具体计算时，需要相关的平衡数据。若手算，人 工查图或查表；若机算，则可将图或表上的相关数据 进行经验回归，得到经验回归方程xA* = f (pA) or pA*= f (xA) 提供于计算机使用。 ⑷ Conclusions: a.系统压力不太高时的等温吸收，可认为气体在液体 中的溶解度只取决于该气体的分压； b.吸收操作的适宜条件：低温高压。 8.2.1Solubility at equilibrium ～平衡溶解度

8.2.1 Solubility at equilibrium I 293K 3 Differences of solubility of gases in liquid O2: Oxygen CO,: Carbon Dioxide SO2: Sulphur Dioxide pA=1.38 NH2: Ammonia 85市b1 10°x,kmo/m3 如图,由实验测得T=293K下 图9-3293K下几种气体在水中的溶解度曲线cA SO2,CO2,NH3andO2在水中的溶 图中横坐标10°cA中的n值如下: 解度曲线。显然,在一定温度和分 气体0 0 压下,不同气体得溶解度相差很大。 例:气相溶质的分压p=20kPa时,水中溶质的平衡浓度 对CO2为10°c·(CO2)=0.78,故c(CO2)=0.0078 kmol/m2;对SO2为1·(SO2)=3.37,故c(O2) 0.337 kmol/m3

3 Differences of solubility of gases in liquid O2 : Oxygen CO2 : Carbon Dioxide SO2 : Sulphur Dioxide NH3 : Ammonia 如图, 由实验测得T=293 K下 SO2 , CO2 , NH3 and O2 在水中的溶 解度曲线。显然，在一定温度和分 压下，不同气体得溶解度相差很大。 8.2.1 Solubility at equilibrium