426 Fermentation and Biochemical engineering handbo 5.0 PROCESS CONSIDERATIONS 5.1 Design Factors The engineer designing an ion exchange column operation usually will prefer to work with the simplest kinetic model and linear driving force approximations. The weakness of this approach is that any driving force law only regards the momentary exchange rate as a function of the solute concentration in the bulk solution and the average concentration in the article, neglecting the effect of concentration profiles in the particle Nevertheless, the linear driving force approach provides an approximation that is sufficiently accurate for the engineer 5.2 Scaling-up Fixed Bed Operations Rodrigues[ 66 has presented empirical and semi-empirical approaches In feedstream is co and the flow-rate is uo. The breakthrough point is usually set at the point where the effluent concentration increases to 5%of co. The design equations relate the total equilibrium ion exchange capacity(@)tothe volume of resin required()to the time of breakthrough(tB) In the empirical approach, the overall mass balance is given by the Eq(15) v=c0t/(1+8)Q Eq(16) =τ(1+8 (the stoichiometric time) Eq(17) (1-a)Q/E go (the mass capacity factor) Eq(18) τ=EW/a0 and v is the bed volume with void space e It is usually necessary to modify this resin amount by a safety fact (1. 2 to 1.5)to adjust for the portion of the total equilibrium capacity that can actually be used at flow rate u and to adjust for any dispersive effects that might occur during operation
426 Fermentation and Biochemical Engineering Handbook 5.0 PROCESS CONSIDERATIONS 5.1 Design Factors The engineer designing an ion exchange column operation usually will prefer to work with the simplest kinetic model and linear driving force approximations. The weakness ofthis approach is that any driving force law only regards the momentary exchange rate as a hnction of the solute concentration in the bulk solution and the average concentration in the particle, neglecting the effect of concentration profiles in the particle. Nevertheless, the linear driving force approach provides an approximation that is sufficiently accurate for the engineer. 5.2 Scaling-up Fixed Bed Operations Rodrigues[66] has presented empirical and semi-empirical approaches which may be used to design ion exchange columns when the solute in the feedstream is co and the flow-rate is uo. The breakthrough point is usually set at the point where the effluent concentration increases to 5% of co. The design equations relate the total equilibrium ion exchange capacity (e) to the volume of resin required (V,) to the time of breakthrough (b). In the empirical approach, the overall mass balance is given by the equation: where Eq. (16) t, = 5 (1 + 5) (the stoichiometric time) Eq. (17) 5 = (1- &)e/& Qo (the mass capacity factor) Eq. (18) 5 = &VhO (the space time) and Vis the bed volume with void space E. It is usually necessary to modify this resin amount by a safety factor (1.2 to 1.5) to adjust for the portion of the total equilibrium capacity that can actually be used at flow rate u and to adjust for any dispersive effects that might occur during operation
Ton Exchange 427 The semi-empirical approach involves the use of the mass transfer zones. This approach has been described in detail specifically for ion exchange resins by Passino. [67 He referred to the method as the operating line andregenerating line process design and used a graphical description to solve the mass transfer problems For the removal of Cat+ from a feedstream, the mass transfer can be modeled using Fig. 21. The upper part shows an element of ion exchange column containing a volume v of resin to which is added a volume Ver of the feedstream containing Ca**. It is added at a flow rate(Fi) for an exhaustion time tex. The concentration of Ca* as it passes through the column element is reduced from Mexi to rex2. Therefore, the resin, which has an equilibrium ion exchange capacity C, increases its concentration of Ca"?? to yexl In this model, fresh resin elements are continuously available at a flow rate (F)=v/o, which is another way of saying the mass transfer zone passes down through the column The lower part of Fig. 21 shows the operating lines for this process The ion exchange equilibrium line describes the selectivity in terms of a Freundlich, Langmuir or other appropriate model The equations for the points in the lower part are given by Eq (19) rex1=ro Ca* in the feedstream) Eq(20) yerl =yes2+(erl -xex2)over Eq(21) X (average Ca in the effluent) Eq(22) (Ca in the regenerated resin) and the slope of the operating line D : ver2 CF
Ion Exchange 427 The semi-empirical approach involves the use of the mass transfer zones. This approach has been described in detail specifically for ion exchange resins by Passin0.[~'1 He referred to the method as the operating line and regenerating line process design and used a graphical description to solve the mass transfer problems. For the removal of Ca" from a feedstream, the mass transfer can be modeled using Fig. 21. The upper part shows an element of ion exchange column containing a volume v of resin to which is added a volume V, of the feedstream containing Ca". It is added at a flow rate (Q) for an exhaustion time t, . The concentration of Ca* as it passes through the column element is reduced from xal to x,,. Therefore, the resin, which has an equilibrium ion exchange capacity Cy increases its concentration of Catt fromy,, to yal. In this model, fresh resin elements are continuously available at a flow rate (F') = v/t, , which is another way of saying the mass transfer zone passes down through the column. The lower part of Fig. 21 shows the operating lines for this process. The ion exchange equilibrium line describes the selectivity in terms of a Freundlich, Langmuir or other appropriate model. The equations for the points in the lower part are given by: Eq. (19) Xexl =xo (Ca" in the feedstream) (Ca" in the exhausted streamstream) x dv x,, (average Ca* in the effluent) = - v, Eq. (21) Eq. (22) Yd=O (Ca" in the regenerated resin) and the slope of the operating line:
428 Fermentation and Biochemical engineering Handb N0】 F N。】 88 色5
428 Fermentation and Biochemical Engineering Handbook .- 5 ti; C Q) 01 E -
Ton Exchange 429 The value of co, C and v are known so that for any Ver value, the slope of the operating line can be calculated from Eq. 23. The specific points: ro is given, xen is obtained by graphicintegration from the breakthrough curves After operation and regeneration, the value of yer? may not be zero but may be between 0.02 and 0.05 if the regeneration is not complete. The application of this technique has been described in terms of basic design parameters such as number of transfer units, the height of a transfer unit and mass transfer fficient. [65 The data generated with the laboratory column may be scaled-up to commercial size equipment. Using the same flow rate(on a mass basis)as used in the laboratory experiments, the appropriate increase in column size over that used in the laboratory is a direct ratio of the volumes to be treated compared to that treated in the laboratory equipment If a reasonable height to diameter ratio(approximately 1: 1)is obtained in the scaleup using the bed depth involved in the laboratory procedure, then that bed depth is maintained and the cross-sectional area of the column is increased. However, if the sizing is such that the column is much larger diameter than the bed depth, scaleup should be done to maintain a height to diameter ratio of approximately 1. The required resin volume is determined by maintaining the san flow conditions(liters of feed solution minute per cubic meter of installed resin) as was used in the laboratory operation Appropriate tank space must be left to accommodate the backwash operation. This is typically 50% of bed depth for cation exchange resins and 100% expansion in the case of anion exchange resins 5.3 Sample Calculation The purification of lysine-HCl from a fermentation broth will be used to illustrate the calculations involved in scaling-up laboratory data The laboratory fermentation broth, which is similar to the commercial contained 2.0 g/0. 1 l lysine, much smaller amounts of Ca", K and amino acids. The broth was passed through 500 ml of strong acid cation resin, Dowex(R HCR-S, in the NH4 form. The flow rate was 9 ml/min 1.77 mI min per cm of resin. It was determined that the resin capacity averaged 115 g of lysine-HCl per liter of resin. It may be noted that since the equivalent molecular weight of lysine-HCl is 109.6 g and the theoretical capacity of Dowex(B HCR-S is 2.0 meq/ml, the operating capacity is 52%of eoretical capacit
Ion Exchange 429 The value of c,,, C and v are known so that for any V, value, the slope of the operating line can be calculated from Eq. 23. The specific points: x, is given, x, is obtained by graphic integration fromthe breakthrough curves. After operation and regeneration, the value ofy,, may not be zero but may be between 0.02 and 0.05 ifthe regeneration is not complete. The application of this technique has been described in terms of basic design parameters such as number of transfer units, the height of a transfer unit and mass transfer coefficient. [as1[691 The data generated with the laboratory column may be scaled-up to commercial size equipment. Using the same flow rate (on a mass basis) as used in the laboratory experiments, the appropriate increase in column size over that used in the laboratory is a direct ratio of the volumes to be treated compared to that treated in the laboratory equipment. If a reasonable height to diameter ratio (approximately 1 : 1) is obtained in the scaleup using the bed depth involved in the laboratory procedure, then that bed depth is maintained and the cross-sectional area of the column is increased. However, if the sizing is such that the column is much larger in diameter than the bed depth, scaleup should be done to maintain a height to diameter ratio of approximately 1. The required resin volume is determined by maintaining the same mass flow conditions (liters of feed solution per minute per cubic meter of installed resin) as was used in the laboratory operation. Appropriate tank space must be left to accommodate the backwash operation. This is typically 50% of bed depth for cation exchange resins and 100% expansion in the case of anion exchange resins. 5.3 Sample Calculation The purification of lysine-HC1 from a fermentation broth will be used to illustrate the calculations involved in scaling-up laboratory data. The laboratory fermentation broth, which is similar to the commercial broth, contained 2.0 g/O. 1 1 lysine, much smaller amounts of Caw, Kf and other amino acids. The broth was passed through 500 ml of strong acid cation resin, DowexB HCR-S, in the NH,’ form. The flow rate was 9 ml/min or 1.77 mVmin per cm2 of resin. It was determined that the resin capacity averaged 1 15 g of lysine-HC1 per liter of resin. It may be noted that since the equivalent molecular weight of lysine-HC1 is 109.6 g and the “theoretical” capacity of DowexB HCR-S is 2.0 meq/ml, the operating capacity is 52% of theoretical capacity
430 Fermentation and Biochemical Engineering Handbook The commercial operation must be capable of producing 9,000 metric tons of lysine(as lysine-dihydrochloride-H2O) per year. With a 2.0 g/0.1 I concentration oflysine in the fermentation broth, the number of liters of broth to be treated each year are 9, 000 m tons 146.19(MW of lysine) 237. 12(MW ofL-HCl-H20 Eq,(24) x011×108=217×10/yx If the plant operates 85% of the time, the flow rate would have to be 27.7×1071x-1 0.85365days I day =3.73×1041/hr 24 hr avaii At a resin capacity of 115 g/l of resin, the amount of resin that must be I(resin) 219.12(MW of L-HCI.2.0 g 115g 146.19( MWof L)0.11 Eq(26) 3.73×104l/hr 9.71×103l/hr hr To obtain the maximum utilization of the resin in this operation, series bed operation(Carrousel)operation is recommended. This operation uses three beds of resin in a method having two beds operating in series while the product is being eluted from the third. The freshly regenerated resin is placed in the polishing position when the totally loaded lead bed is removed for
430 Fermentation and Biochemical Engineering Handbook The commercial operation must be capable of producing 9,000 metric tons of lysine (as lysinedihydrochloride-H,O) per year. With a 2.0 g/O. 1 1 concentration of lysine in the fermentation broth, the number of liters of broth to be treated each year are: 9,000 m tons 146.19 (MW of lysine) X Yr 237.12 (MWofL-HCl-H,O) x- Os1 x- lo6g = 27.7 x 107 i/p 2.0g Mton If the plant operates 85% of the time, the flow rate would have to be: 27.7 x lo7 l/yrxlx 1Yr 0.85 365 days 1 day 24 hr -=3.73x104 l/hr At a resin capacity of 1 15 g/1 of resin, the amount of resin that must be available is: l(resin) 219.12(MWof L-HCl) x-x 2.0g 115 g 146.19(MWof L) 0.1 1 3’73x1041/hr =9.71~103 l/hr hr To obtain the maximum utilization of the resin in this operation, series bed operation (Carrousel) operation is recommended. This operation uses three beds of resin in a method having two beds operating in series while the product is being eluted from the third. The freshly regenerated resin is placed in the polishing position when the totally loaded lead bed is removed for regeneration