中国科技论文在线 http://www.paper.edu.cn Chemical Engineering Science 56 (2001) 6165–6170 www.elsevier.com/locate/ces Optimal operation ofan integrated bioreaction–crystallization process for continuous production of calcium gluconate using external loop airlift columns Jie Baoa, Kenichi Koumatsua, Keiji Furumotob, Makoto Yoshimotoa, Kimitoshi Fukunagaa, Katsumi Nakaoa; ∗ aDepartment of Applied Chemistry and Chemical Engineering, Yamaguchi University, Tokiwadai, Ube, Yamaguchi 755-8611, Japan bOshima National College of Maritime Technology, Oshima, Yamaguchi 742-2106, Japan Abstract A kinetic model was proposed to optimize the integrated bioreaction–crystallization process newly developed for production of calcium gluconate crystals using external loop airlift columns. The optimal operating conditions in the bioreactor were determined using an objective function deÿned to maximize the productivity as well as to minimize biocatalyst loss. The optimization of the crystallizer was carried out by matching the crystallization rate to the optimal production rate in the bioreactor because the bioreaction was found to be the rate controlling process. The calcium gluconate productivity under the optimal conditions of the integrated process was obtained by the simulation based on the process model. The productivity ofthe proposed process was found to be comparable to that ofthe current batch fermentationprocess. ? 2001 Elsevier Science Ltd. All rights reserved. Keywords: Process kinetic model; Optimization; Calcium gluconate; Bioreaction–crystallization process; Immobilized glucose oxidase; Biocatalyst deactivation 1. Introduction crystallization kinetics were studied in the authors’ pre- vious works (Nakao et al., 1991; Nakao, Kiefner, Furu- In this work, a new environment friendly bioprocess moto, & Harada, 1997; Nakao, Bao, Harada, Yasuda, & for the continuous production of calcium gluconate crys- Furumoto, 2000a; Nakao et al., 2000b; Nakao, Koumatsu, tals has been proposed using the immobilized glucose ox- Bao, Yoshimoto, & Fukunaga, 2000c; Bao, Furumoto, idase catalyzed oxidation ofglucose. The new integrated Fukunaga, & Nakao, 2000). The purpose ofthis study bioreaction–crystallization process employs two external is to develop an overall process model for the integrated loop airlift bubble columns in series, one being bioreac- bioreaction–crystallization process, and then to optimize tor and the other crystallizer. The bioreactor is used to the operating conditions through the objective function produce calcium gluconate from the oxidation of glucose deÿned so as to obtain the maximum productivity at the catalyzed by the immobilized glucose oxidase plus man- minimum loss ofbiocatalyst. Finally, the advantages of ganese dioxide gel beads. The output from the bioreactor the new process have been demonstrated by comparing it is then fed into the crystallizer to produce the calcium with the current batch fermentation process (Milsom & gluconate crystals. The enzymatic reaction kinetics, the Meers, 1985; Rao & Panda, 1993). 9ow and mixing behaviors ofthe immobilized glucose oxidase gel beads, the gas–liquid and liquid–solid oxygen transfer properties, the deactivation kinetics of the immo- 2. Process development and design equations bilized glucose oxidase plus manganese dioxide, and the 2.1. Reaction scheme and process 0owsheet ∗ Corresponding author. Tel.: +81-836-85-9271; fax: +81- 836-85-9201. The reaction scheme for production of calcium glu- E-mail address: [email protected] (K. Nakao). conate is composed ofthree separate reactions, the 0009-2509/01/$ - see front matter ? 2001 Elsevier Science Ltd. All rights reserved. PII: S 0009-2509(01)00272-X 转载 中国科技论文在线 http://www.paper.edu.cn 6166 J. Bao et al. / Chemical Engineering Science 56 (2001) 6165–6170 immobilized glucose oxidase catalyzed oxidation ofglu- CE and CM as well as eKectiveness factors and , ac- cose (1), the hydrogen peroxide decomposition (2) cat- cording to Eqs. (10)–(13). alyzed by the immobilized manganese dioxide, and the (2) Deactivation kinetics of immobilized glucose oxidase neutralization ofgluconic acid with calcium hydroxide and manganese dioxide (Nakao et al., 2000b): (3). The overall reaction is represented by reaction (4) −5 under the steady state ofoxygen and hydrogen peroxide −(dCE=dt)=kdCE =(9:79 × 10 [pH] concentrations: −4 −3:79 × 10 )CPS CE; (10) Glucose(G)+O + H O 2 2 −3 −(dCM =dt)=kdCM =(1:13 × 10 GO →Gluconic acid(GA)+H2O2(P); (1) −4 −1:57 × 10 [pH])CPS CM : (11) MnO2 1 (3) Correlations of initial and k values (Nakao H2O2(P) → H2O + O2; (2) P 2 et al., 1991): 1 ln = ln(9:890 × 10−3[pH] − 3:149 × 10−2) Gluconic acid(GA)+ 2 Ca(OH)2 1 −0:405 ln CG − 0:244 ln CE; (12) → 2 Calcium gluconate(CaG)+H2O2; (3) −3 −2 1 1 kP =63:42CM − 9:024 × 10 [pH]+7:104 × 10 : Glucose(G)+ O2 + Ca(OH)2 2 2 (13) → 1 Calcium gluconate(CaG)+H O: (4) 2 2 (4) Correlations of mass transfer properties with oper- The schematic ofthe proposed process is shown in ating parameters (Bao et al., 2000): Fig. 1. The highly concentrated calcium gluconate solu- k a =2:567 × 10−2 +1:021 ln U ; (14) tion produced in the bioreactor is fed into the crystallizer ln L G in which the product is crystallized for its recovery. The mother liquid ofthe crystallizer is recycled to the biore- ln kS = − 4:018+0:276 ln UG: (15) actor. Hence, the feed of solid glucose and calcium hy- (5) Crystallization kinetics of calcium gluconate from droxide to the bioreactor with simultaneous removal of reaction solution (Nakao et al., 2000c): calcium gluconate crystals from the crystallizer realizes a continuous production ofthe crystals with almost no dCCaG=dt =2CS (1=LS +1=rS )Kg[CCaG − 2:61 waste eIuents. ×105 exp(−2:64 × 103=T)]3:16; (16) 2.2. Design equations where the crystallization rate constant Kg =(6:35 × 10−12[pH] − 2:47 × 10−11) exp(−8:71 × 103=T). (1) Mass transfer and reaction kinetic equations (Nakao et al., 1991): 2.3. Objective function for overall process optimization dC =dt =(−dC =dt)=2 (5) CaG G The objective function was deÿned as the ratio of the calcium gluconate productivity to the catalyst cost dur- = kLa(COi − COS ) (6) ing the operation period equal to half-life of the immo- bilized glucose oxidase CE;t1=2(= ln 2=kd) as shown in ∗ Eq. (17). The cost consists ofthe immobilized glucose = kS aS (COS − C )(VS =VL) (7) OS oxidase and manganese dioxide deactivated per calcium ∗ gluconate produced. The unit ofthe objective functionis 1 VM C VS OS 2 3 = ∗ (8) mol =(m $). 2 COS + KM (1 + CPS =KI ) VL Objective = k C (V =V )=2; (9) P PS S L t1=2 dCCaG where the apparent Michaelis constant KM = kmO=(1 + = dt 0 dt kmG=CG), the maximum reaction rate VM = kCATCE=(1 + t t kmG=CG), the competitive inhibition constant KI which 1=2 dC 1=2 dC P − E dt CaG dt was found to be almost equal to KM . The three unknown GO dt dt variables C , C∗ , and C can be determined by rear- 0 0 OS OS PS ranging the equations, Eqs. (7)–(9), taking into account t1=2 dC t1=2 dC + P − M dt CaG dt the progressive change ofthe catalyst concentrations MnO2 0 dt 0 dt 中国科技论文在线 http://www.paper.edu.cn J. Bao et al. / Chemical Engineering Science 56 (2001) 6165–6170 6167 Fig. 1. Schematic diagram ofintegrated bioreaction–crystallization process forproduction ofcalcium gluconate crystals. 2 t1=2 t1=2 dCCaG dCE 5 to 6 (Nakao et al., 1991). In the immobilized glucose = dt − dtPGO oxidase catalyzed reaction, the same optimal temperature 0 dt 0 dt of30 ◦C was also adopted. However, the optimal pH value t1=2 dC had to be changed because the immobilized manganese + − M dtP ; (17) dt MnO2 dioxide reacted with the produced hydrogen peroxide in 0 the acidic solution. Fig. 2 shows the eKect ofpH value on where P and P are the molar prices ofglucose GO MnO2 the deactivation ofthe immobilized glucose oxidase and 6 oxidase (PGO is $9 × 10 =mol) and manganese dioxide manganese dioxide. The lower pH was favorable for the (P is $12.5=mol), respectively. Maximization ofthe MnO2 enzyme stability as shown in Fig. 2(a). On the other hand, objective function means the maximum production of cal- Fig. 2(b) shows that the immobilized manganese dioxide cium gluconate at the minimum loss ofbiocatalyst in the deactivates faster at the lower pH value. To perform the bioreactor. Because the bioreaction was found to be the prolonged practical operation, therefore, pH 7 was taken rate controlling step for the overall process, the optimiza- as the optimal one in spite ofa lower enzyme stability. tion ofthe crystallizer could be achieved by matching the crystallization rate to the optimal production rate in the bioreactor. Thus, it is easier and more 9exible to carry 3.2. Determination of optimal conditions in bioreactor out the calculation in a separate calculation tool than to with objective function use the process simulation system like Aspen or Hysys. Aspen or Hysys is very eNcient on the 9owsheet simu- The glucose concentration CG, the immobilized glu- lation and optimization, but shows no advantage for the cose oxidase concentration CE, the manganese dioxide optimization calculation in a single special operation unit concentration CM , the gel beads loading S , and the su- which is not the standard modular ofthe package. Be- perÿcial gas velocity UG were changed in their practical sides, the calculation using Aspen or Hysys needs to build range to maximize the objective function. many Fortran blocks to describe the particular reaction Fig. 3(a) shows that the objective function decreases and deactivation kinetics, mass transfer behaviors etc. with increasing CE. This suggests that the lowest possi- ble CE is most favorable for the maximum productivity with the minimum biocatalyst loss, because the lower CE 3. Results and discussion is favorable for the less accumulation of hydrogen per- oxide.