Acarbose Isolation with Gel Type Strong Acid Cation Exchange Resin: Equilibrium, Kinetic and Thermodynamic Studies

SEPARATION SCIENCE AND ENGINEERING Chinese Journal of Chemical Engineering, 21(10) 1106—1113 (2013) DOI: 10.1016/S1004-9541(13)60583-2

Acarbose Isolation with Gel Type Strong Acid Cation Exchange Resin: Equilibrium, Kinetic and Thermodynamic Studies* WANG Yajun (王亚军)1,2, YU Lei (于蕾)1,2, ZHENG Yuguo (郑裕国)1,2,**, WANG Yuanshan (王远山)1,2 and SHEN Yinchu (沈寅初)1,2 1 2

Institute of Bioengineering, Zhejiang University of Technology, Hangzhou 310014, China Engineering Research Center of Bioconversion and Biopurification, Ministry of Education, Zhejiang University of Technology, Hangzhou 310014, China

Abstract Acarbose, a potent α-glucosidase inhibitor, is widely used as an oral anti-diabetic drug for the treatment of the type 2, non-insulin-dependent diabetes. In this work, a gel type strong acid cation exchange resin 001×4 was applied to isolate acarbose from fermentation broth. It was demonstrated that cation exchanger 001×4 displayed a large adsorption capacity and quick exchange rate for acarbose. The static adsorption equilibrium data were well fitted to the Langmuir equation. Column adsorption experiments demonstrated that high dynamic adsorption capacity was reached at bed height of 104.4 mm, feed flow rate of 1.0 ml·min−1 and acarbose concentration of 4.0 mg·ml−1. Under the optimized conditions, the column chromatography packed with cation exchanger 001×4 recovered 74.3% (by mass) of acarbose from Actinoplanes utahensis ZJB-08196 fermentation broth with purity of 80.1% (by mass), demonstrating great potential in the practical applications in acarbose separation. Keywords acarbose, separation, cation exchange, chromatography

1

INTRODUCTION

Diabetes is a major chronic disease that has significant negative individual and societal impacts. As a potent α-glucosidase inhibitor, acarbose delays glucose release from complex carbohydrates, significantly reduces postprandial blood glucose levels, and is being clinically used to combat the type 2, non-insulindependent diabetes [1]. Moreover, it has been shown to prevent or delay high blood pressure and cardiovascular complications among individuals with impaired glucose tolerance [2]. Structurally, acarbose is a complex pseudo-oligosaccharide and consists of acarviose and maltose moieties. Acarviose, the main unit of acarbose, is of principal value for α-glycosidase’s inhibitory function. Due to the presence of intramolecular nitrogen in acarbose structure, it possesses a secondary amino group and has two pKa values of 5.1 and 12.39, contributing to practical application of ion exchange in acarbose separation [3-9]. In the 1980s, macroporous strong acid cation exchangers were firstly applied in acarbose separation [5, 6]. Rodriguez et al. elucidated the mechanisms of chemisorption and ion exchange in the acarbose adsorption on strong acid cation exchange resins [4]. Weakly acid cation exchanger with carboxyl groups was later introduced in acarbose isolation. Their applications were limited for narrow operation pH range requirement [9]. Mihaljevic et al. introduced cation exchangers based on sepharose matrix. Nevertheless, these media were too expensive for industrial application [8]. Since efficient separation process is a constant

requirement in the fermentation industry, it is of necessity to enhance acarbose separation efficiency. Gel type strong acid cation exchange resin 001×4 showed high mass transfer, large adsorption capacity, quick exchange rate and good mechanical strength. Due to these favorable features, cation exchanger 001×4 is extensively used in industrial separation processes. Besides, it is being used in discoloring and desalting in food industry, and as catalyst in chemical industry. Our group has conducted detailed researches on acarbose fermentation with Actinoplanes utahensis ZJB-08196 [10, 11]. The purpose of this research was to investigate the feasibility of using cation exchanger 001×4 in acarbose recovery from fermentation broth. The adsorption isotherm, adsorption kinetics and breakthrough behavior of acarbose on cation exchanger 001×4 were studied. 2 2.1

EXPERIMENTAL Material

Gel type strong acid cation exchange resin 001×4 was provided by Jiangsu Linhai Resin Technology Company (Jiangsu, China). Acarbose with a purity of 95% was generously presented by Huadong Medicine Co. Ltd. (Hangzhou, China). Acetonitrile was purchased from J&K Scientific Ltd. (Beijing, China), hydrochloric acid (38%, by mass) from Juhua Reagent Co., Ltd. (Quzhou, China), and sodium hydroxide from Xiaoshan Chemical Reagent Company (Hangzhou, China).

Received 2012-04-22, accepted 2012-09-20. * Supported by the National Basic Research Program of China (2011CB710800) and National Special Program for Key Science and Technology of China (2008ZX09204-004). ** To whom correspondence should be addressed. E-mail: [email protected]

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2.2 Preparation and pretreatment of A. utahensis ZJB-08196 fermentation broth The fermentation broth of A. utahensis ZJB-08196 was prepared as our previously work [10, 11], and centrifuged at 9000 r·min−1 for 10 min to remove mycelia at room temperature with a Beckman tabletop centrifuge (Beckman, USA). In order to reduce impurities interference for column chromatography, proteins in the supernatant were removed by alcohol precipitation with four volumes of 75% ethanol (by volume). Afterward, the solution was concentrated to 3.57 mg·ml−1 acarbose using a rotary evaporator. After adjusted to pH 6, the clarified acarbose cell-free broth was kept at 277K till the subsequent acarbose separation. 2.3

Adsorption experiments

2.3.1 Static adsorption Adsorbent 001×4 was soaked in 10.0% NaCl solution for 4 h to swell enough and remove impurities, and subsequently treated with 1.0 mol·L−1 HCl, 1.0 mol·L−1 NaOH. Afterward, it was washed thoroughly with distilled water to pH7.0. The pretreated resin was dried to remove redundant free water under vacuum. For isotherm tests, 50.0 mg pretreated adsorbent 001×4 was added into 25 ml conical flask containing 10.0 ml acarbose solutions at concentrations between 1.0 and 10.0 mg·ml−1. Suspensions were shaken on a shaker at 200 r·min−1 and 298 K for 24 h (this time is enough to reach the equilibrium). An aliquot of 50 μl was withdrawn from each suspension for acarbose determination by HPLC method. As acarbose ionization was pH-dependent, effect of pH on acarbose adsorption was examined in a pH range of 3.0-12.0 at 298 K. The pH of suspensions was adjusted with 1.0 mol·L−1 HCl or 1.0 mol·L−1 NaOH. Temperature effect on acarbose adsorption equilibrium was conducted at 293 K, 298 K, 303 K and 308 K with pH of 5.9 (high adsorption capacity at this pH). The equilibrium adsorption capacity of adsorbent 001×4 for acarbose, qe (mg·g−1 dry resin), was calculated as follows. (c − c ) v qe = 0 e (1) m where c0 (mg·ml−1) and ce (mg·ml−1) are the acarbose initial and equilibrium liquid-phase concentrations, and m (g) is the mass of the dry adsorbent 001×4. v (ml) is the volume of the solution. 2.3.2 Adsorption isotherm model Process design and optimization of ion exchange chromatograph are always based on adsorption isotherms. In this work, the Langmuir isotherm was used, which was based on the hypothesis of monolayer surface adsorption with uniform energies at homogeneous sites, and extensively used to describe ion exchange equilibrium [12]. It is represented as Eq. (2):

qe =

qm kL ce 1 + kL ce

(2)

where qm (mg·g−1) is the maximum adsorption capacity and kL (L·mg−1) is the Langmuir isotherm constant. 2.4

Batch adsorption experiments

Acarbose adsorption kinetic experiments were conducted in 250 ml Erlenmeyer flasks with 1.00 g pretreated adsorbent 001×4 and preheated acarbose solutions at initial concentration of 2.0, 4.0, 6.0 and 8.0 mg·ml−1, respectively. To each 250 ml Erlenmeyer flask, 100 ml of acarbose solution was added, and stirred at 300 r·min−1 and 298 K for 60 min. An aliquot of 50 μl was taken at an interval of 5 min for acarbose analysis. The adsorption capacity of acarbose on dry resin, qt (mg·g−1), at time t (min) was obtained from Eq. (3). qt =

( c0 − ct ) v

(3) m where c0 (mg·ml−1) and ct (mg·ml−1) are the acarbose concentrations at initial and time t (min), respectively; v (ml) is the volume of the acarbose solution, and m (g) is the mass of the dry resin. 2.4.1 Pseudo-first-order model The pseudo-first-order model is one of the earliest equations to describe adsorption rate based on the adsorption capacity. It is represented as Eq. (4) [13]. kt lg ( qe − qt ) = lg qe − 1 (4) 2.303 where qe (mg·g−1) and qt (mg·g−1) are the adsorption capacity at equilibrium and at time t (min), respectively. k1 (min−1) is the adsorption rate constant of the pseudo-first-order model, which can be regressed from the straight lines of lg (qe − qt) versus t. 2.4.2 Pseudo-second-order model Pseudo-second-order model has been applied to estimate k2 and qe with Eq. (5) [14]. t 1 t = + (5) 2 qt k2 qe qe

where k2 (g·mg−1·min−1) is the pseudo-second-order rate constant of adsorption reaction; qe − qt, the driving force, indicates the fraction of the available sites on adsorbent. The term k2 qe2 is defined as h (mg·g−1·min−1), denoting the initial adsorption rate as t/qt approaches 0. From the straight lines of t/qt versus t, k2 can be obtained. 2.5

Breakthrough experiments

The breakthrough experiments were conducted in sealed glass columns with inner diameter of 1.0 cm

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and length of 20.0 cm. Three grams of pretreated adsorbent 001×4 was weighted and packed into the column at a total bed volume of 3.38 ml. The fixed bed was washed with distilled water at a flow rate of 1.0 ml·min−1 until the bed height was stable. Acarbose solutions of 2.0, 4.0, 6.0 mg·ml−1 were continuously pumped into the column at 0.6 ml·min−1 and 303 K. Effect of flow rate on breakthrough curves was examined in a similar way, ranging from 0.6 ml·min−1 to 1.5 ml·min−1. Impact of bed depth was studied in a range of 40 mm to 105 mm at 1.0 ml·min−1 and 303 K. Column temperature was regulated by a temperature controller, and flow rates were adjusted via a peristaltic pump. Samples were collected for eluate acarbose detection. 2.6

Analytical methods

Acarbose concentration was determined with a Shimadzu LC-10AT HPLC system, which consisted of a manual 20 µl loop injector, a LC-20AD pump and SPD-20A detector. Separation was achieved on an amino column (250 mm×4.6 mm, 5μm, Elite, China). Column temperature was maintained at 40 °C with a CTO-10AS heater (Shimadzu, Japan). Since acarbose is spectroscopically silent at convenient wavelengths except the end absorption, absorbance wavelength for the SPD-20A detector was set at 210 nm [15]. The mobile phase was made of acetonitrile and pH7.0, 6.3 mmol·L−1 phosphate buffer at a volumetric ratio of 70︰30, and run at 1.0 ml·min−1 [10]. Samples were centrifugated at 14000 r·min−1 and then subjected to microfiltration against 0.45 μm membrane, and a 20 μl of the resultant filtrate was loaded into the HPLC system for a single run. 2.7

Thermodynamic investigations

The thermodynamic parameters, including Gibbs free energy change ∆G0 (kJ·mol−1), enthalpy change ∆H0 (kJ·mol−1) and entropy change ∆S0 (kJ·mol−1·K−1) are estimated to explain acarbose adsorption process. ∆G0 is related to the equilibrium constant, and thus ∆H0 (kJ·mol−1) and ∆S0 are regressed through van’t Hoff equation [16, 17]. ΔH 0 ΔS 0 + (6) RT R where R (8.314 J·mol−1·K−1) is the gas constant and k0 is the thermodynamic equilibrium constant for the adsorption process. ln k0 = −

3 3.1

Figure 1 The Langmuir isotherm of acarbose adsorption onto cation exchanger 001×4 (c0 varied between 1.0 mg·ml−1 and 10.0 mg·ml−1, v = 10 ml, m = 0.05 g, 298 K, pH 5.9)

RESULTS AND DISCUSSION Equilibrium study

As shown in Fig. 1, Langmuir model well fits the experimental data with R2 value of 0.996 with the

adsorption capacity qm of cation exchanger 001×4 peaking at 554.9 mg·g−1. 3.1.1 pH Due to the presence of intramolecular nitrogen in acarbose structure, it possesses a secondary amino group and has two pKa values of 5.1 and 12.39 [15]. It is reasonable that pH affects acarbose ionization and physisorption via electrostatic interactions. Totally, three acarbose species exist in aqueous solution, which are cationic form of acarbose, undissociated acarbose and the anion form of acarbose [15]. Impact of pH on the equilibrium isotherms for acarbose adsorption on cation exchanger 001×4 is shown in Fig. 2 (a). Weak acidic condition is advantageous to acarbose adsorption on adsorbent 001×4 with a maximum adsorption capacity at pH 5.9. According to the theoretical concentration distribution functions of acarbose species in aqueous solution at room temperature [15] and pH 5.9, 86.32% acarbose molecules are in the cation form, 13.68% in the undissociated form, and only 0.00279% in the anion form. Moreover, it is notable that, besides cation exchange, chemisorption takes place via an acid/base neutralization reaction between the active acid sites of the strong acid resins and acarbose secondary amino group with a pair of odd electrons [4]. 3.1.2 Temperature Temperature is an important factor influencing adsorption performance. Effect of temperature on the adsorption capacity of acarbose is shown in Fig. 2 (b). Static adsorption capacity increases with increasing temperature from 293 K to 308 K, related to the contribution of chemisorptions and endothermic nature. Another explanation is that raising temperature increases adsorption energy, contributing to higher adsorption capacity. The dimensionless constant separation factor, RL, is defined in Eq. (7). It is an indicative factor for favorable adsorption or unfavorable adsorption [18]. 1 RL = (7) 1 + kL c0 where c0 (mg·ml−1) is the initial concentration and kL

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(a) (b) pH 3.0; ● pH 5.9; □ pH 7.0;○ pH 12.0 △ 293 K; ● 298 K; □ 303 K; ■ 308 K Figure 2 Effect of pH (a) and temperature (b) on the adsorption capacity of acarbose onto cation exchanger 001×4 (c0 = 1-10 mg·ml−1, v = 10 ml, m = 0.05 g) ▲

(a) (b) △ 293 K; ● 298 K; □ 303 K; ■ 308 K Figure 3 The plot of lnk0 vs. 1/T for the determination of thermodynamic parameters for acarbose on cation exchanger 001×4

is the Langmuir constant. RL denotes the characteristics of the adsorption: unfavorable for RL>1, linear for RL = 1, favorable for 0
(Table 1), suggesting that acarbose adsorption on 001×4 is mainly attributed to chemisorption. The positive value of ∆H0 reveals that the adsorption process is endothermic in nature. The positive value of ∆S0, 0.48 kJ·mol−1 (Table 1), indicates that the degree of freedom increases at solid-liquid interface during the acarbose adsorption. In addition, the thermodynamic equilibrium constant k0 increases with temperature.

Thermodynamic parameters

As shown in Table 1, in the case of acarbose adsorption on adsorbent 001×4, the ∆G0 value was between −1.14 kJ·mol−1 and −8.34 kJ·mol−1. Moreover, the absolute value of ∆G0 increased with increasing temperature, confirming that adsorption is a spontaneous process and more favorable at high temperatures. The values of k0 are obtained from the intercept of the ce/qe versus ce at different temperatures [20, 21] as illustrated in Fig. 3 (a). The ∆S0 and ∆H0 values are regressed from the plot of lnk0 versus 1/T [Fig. 3 (b)]. Commonly, ∆H0 for physical adsorption is in the range of 2.1 kJ·mol−1 to 20.9 kJ·mol−1; for chemical reaction, ∆H0 is between 80 kJ·mol−1 and 200 kJ·mol−1 0 −1 [22]. In this case, the value of ∆H is 139.5 kJ·mol

Table 1 Thermodynamic parameters for acarbose adsorption on cation exchanger 001×4 Temp. /K

k0

∆G0 /kJ·mol−1

∆H0 /kJ·mol−1

∆S0 /kJ·mol−1·K−1

R2

293

1.000

−1.14

139.5

0.48

0.986

298

1.001

−3.54

303

1.002

−5.94

308

1.003

−8.34

3.3

Adsorption kinetics

3.3.1 Effect of the initial acarbose concentration As illustrated in Fig. 4, the initial acarbose concentration has a notable influence on adsorption kinetics.

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Figure 4 Influence of initial concentration on adsorption of acarbose onto cation exchanger 001×4 (m = 1.0 g, v = 100 ml, 298 K, 300 r·min−1, pH 5.9) −1 −1 −1 −1 ◇ 2 mg·ml ; ■ 4 mg·ml ; ● 6 mg·ml ; △ 8 mg·ml

◇

2 mg·ml−1;

■

(a) 4 mg·ml−1; ● 6 mg·ml−1;

△

8 mg·ml−1

Acarbose adsorption capacity increases with acarbose concentration. As shown in Fig. 4, acarbose adsorption kinetics typically consists of two distinct stages. In the initial 15 min, adsorption rate is fast, relating to the abundant vacant binding sites available on adsorbent surface. Thereafter, the adsorption rate is slower and reaches equilibrium at about 20 min. Moreover, it is observed that longer equilibrium times are required for higher concentrations of acarbose. 3.3.2 Kinetic study Pseudo-first-order and pseudo-second-order models are applied to depict acarbose adsorption kinetic as illustrated in Fig. 5. The pseudo-first-order equation [Fig. 5 (a)] produces poor fitting. Fitting with the pseudo-second-order equation yields satisfactory correlation coefficients, indicating that acarbose adsorption kinetic on adsorbent 001×4 follows the pseudo-secondorder model [Fig. 5 (b)]. It is confirmed that the pseudo-second-order model is predominant and the overall rate of acarbose adsorption process is controlled by chemisorption [23-25]. 3.4 Acarbose breakthrough in packed column with adsorbent 001×4

◇

2 mg·ml−1;

■

4 mg·ml−1;

(b) 6 mg·ml−1;

●

△

8 mg·ml−1

Figure 5 Pseudo-first-order plot (a) and Pseudo-second-order plot (b) for acarbose adsorption onto cation exchanger 001×4

3.4.1 Influence of initial acarbose concentration Typical sigmoidal shape curves are obtained at varying feed acarbose concentrations as illustrated in Fig. 6. Breakthrough curves become sharper at the high concentrations, and the breakthrough points are advanced with acarbose concentration rising. As summarized in Table 2, the dynamic adsorption capacity for acarbose at the breakthrough point increases with initial acarbose concentrations, but the discrepancy is

Acarbose dynamic adsorption on cation exchanger 001×4 was further investigated. Considering the effect of initial acarbose concentration, feed flow rate and bed height on breakthrough, and the Yoon-Nelson model was adopted to predict the breakthrough. The Yoon-Nelson equation is a well-established semi-empirical adsorption model, and is widely used to fit column adsorption data due to its simplicity, written as Eq. (8) [26]. cout 1 = (8) kY (τ −t ) c0 1 + e where c0 (mg·ml−1) and cout (mg·ml−1) are the initial and sampling concentration at t, kY (min−1) is the rate constant; τ (min) is 50% adsorbate breakthrough time, and t (min) is the sampling time.

Figure 6 Breakthrough curves for different initial concentration (bed height 43.1 mm, u = 0.6 ml·min−1, 303 K, pH 5.9) −1 −1 −1 ○ 2 mg·ml ; ● 4 mg·ml ; △ 6 mg·ml ; Yoon-Nelson

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Table 2

Fittings of breakthrough parameters for acarbose using the Yoon-Nelson model cout/c0

t/min

Capacity/mg·g−1

τ/min

kY×10−2/min−1

R2

2.0

0.058

365

183.4

814.4

0.6

0.996

4.0

0.050

180

192.5

503.5

0.8

0.998

6.0

0.050

135

205.1

411.6

0.8

0.997

0.6

0.059

365

274.7

594.5

1.1

0.998

0.8

0.054

260

262.3

443.9

1.3

0.996

1.0

0.050

220

278.6

390.3

1.3

0.995

1.2

0.053

150

227.3

302.2

1.7

0.997

1.5

0.053

105

198.9

247.4

1.6

0.991

43.1

0.050

220

278.6

390.3

1.3

0.995

104

0.051

315

308.8

465.6

1.6

0.997

Factor initial concentration/mg·ml−1

flow rate/ml·min−1

bed height/mm

small. The rate constant kY of the Yoon-Nelson model also has an increasing tendency towards feed acarbose concentration. On the contrary, τ decreases evidently from 814.4 min to 411.6 min. Considering the breakthrough time, feed acarbose concentration is therefore set at 4 mg·ml−1. 3.4.2 Influence of flow rate Flow rate impact on breakthrough is illustrated in Fig. 7. It is observed that the breakthrough curves are flatter at low flow rates, relating to the effect of film transfer resistance [27]. They are steeper with flow rate rising. Table 2 shows that the adsorption capacity of acarbose on 001×4 is high at flow rate below 1.0 ml·min−1; whereas the flow rate is raised to 1.2 ml·min−1, the 5% breakthrough capacity is markedly decreased from 278.6 mg·g−1 to 227.3 mg·g−1 with a 18.4% loss in adsorption capacity, and the leakage rate is up to 28.6% at rate of 1.5 ml·min−1. This may be due to inadequate contract time for acarbose adsorption. Therefore, 1.0 ml·min−1 is chosen.

and 0.998, indicating that the Yoon-Nelson model reasonably describes the adsorption behavior of acarbose onto adsorbent 001×4. The parameter of kY increases with flow rate, which is related to much acarbose passing through the column at high flow rate [28]. 3.4.3 Influence of bed height The breakthrough curves of acarbose at various bed heights are presented in Fig. 8. The curves show that the breakthrough point is delayed, and the saturation point is brought forward with rising bed height with column efficiency peaking at 9.79% (Table 2). A similar variation in the Yoon-Nelson model fitting is observed for bed height. kY increases as the bed height increases and τ reduces.

Figure 8 Effect of bed height on breakthrough at (c0 = 4.0 mg·ml−1, u = 1.0 ml·min−1, 303 K, pH 5.9) ■ 104.4 mm; ○ 43.1 mm; Yoon-Nelson

Figure 7 Effect of flow rate on breakthrough (c0 = 4.0 mg·ml−1, bed height = 43.1 mm, 303 K, pH 5.9) 0.6 ml·min−1; □ 0.8 ml·min−1; ● 1.0 ml·min−1; △ 1.2 ml·min−1; ○ 1.5 ml·min−1; Yoon-Nelson

Furthermore, the R2 values are between 0.991

3.5 Acarbose isolation from A. utahensis ZJB-08196 fermentation broth

Under the optimized chromatography conditions, 90.0 ml clarified A. utahensis ZJB-08196 fermentation broth supernatant containing 3.57 mg·ml−1 acarbose were pumped into a column (bed volume 18.5 ml) at 1.0 ml·min−1, 303 K. Afterwards, the column was

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Figure 9 Step-wise elution curve of crude acarbose on 001×4 with NH4OH solution (303 K, pH 5.9)

stepwise eluted with deionized water, 30, 50, 70 and 90 mmol·L−1 NH4OH at a flow rate of 1.0 ml·min−1. Eluates were collected at 5.0 ml per tube, and acarbose were determined with HPLC. Results are shown in Fig. 9. It is found that most absorbed acarbose is eluted with 50 mmol·L−1 NH4OH (Fig. 9). This one-step column chromatography recovers 74.3% (by mass) of acarbose in a purity of 80.1% (by mass). The HPLC chromatograms of acarbose before and after cation exchange chromatography shown in Fig. 10 clearly reveal that acarbose purity increases notably. Hence, it is concluded that the cation exchanger 001×4 is efficient in recovering acarbose from A. utahensis ZJB-08196 fermentation broth.

(a)

(b) Figure 10 Chromatograms of acarbose before (a) and after (b) separation on a column packed with 001×4 resin: (a) the supernatant of A. utahensis ZJB-08196 fermentation broth; (b) eluate

4

CONCLUSIONS

The acarbose adsorption on gel type strong acid cation exchange resin 001×4 is spontaneous and endothermic. Both ion exchange and chemisorption mechanisms participate in acarbose adsorption on cation exchanger 001×4, and the isotherms data are well fitted to the Langmuir model. The static acarbose adsorption capacity peaks at 308 K. Moreover, adsorption kinetics follows the pseudo-second-order model. Under the optimized chromatography conditions, cation exchanger 001×4 recovers 74.3% (by mass) of acarbose in a purity of 80.1% (by mass). The chromatograms of acarbose reveals that 001×4 is efficient in removing impurities and enriching acarbose. In conclusion, cation exchanger 001×4 is useful in enrichment and separation of acarbose from fermentation broth, considering its low cost, high adsorption capacity and operational simplicity. It has great potential in the practical applications of acarbose separation. NOMENCLATURE ce cout ct c0 ΔG0 ΔH0 kL kY k0 k1 k2 m

acarbose equilibrium liquid-phase concentrations, mg·ml−1 sampling concentration at t, mg·ml−1 acarbose concentrations at time t, mg·ml−1 acarbose initial liquid-phase concentrations, mg·ml−1 Gibbs free energy change, kJ·mol−1 enthalpy change, kJ·mol−1 Langmuir isotherm constant, L·mg−1 rate constant, min−1 thermodynamic equilibrium constant adsorption rate constant of the pseudo-first-order, min−1 pseudo-second-order rate constant, g·mg−1·min−1 mass of the adsorbent, g

Chin. J. Chem. Eng., Vol. 21, No. 10, October 2013

qe qm qt RL ΔS0 T t v τ

equilibrium adsorption capacity, mg·g−1 maximum adsorption capacity, mg·g−1 adsorption capacity at time t, mg·g−1 dimensionless constant, separation factor entropy change, kJ·mol−1·K−1 temperature, K sampling time, min volume of the solution, ml 50% solution breakthrough time, min

REFERENCES 1 2

3 4

5 6 7 8 9 10

11

12

13

Jermendy, G., “Can type 2 diabetes mellitus be considered preventable?”, Diabetes Res. Clin. Pract., 68 (S1), S73-S81 (2005). Chiasson, J.L., Josse, R.G., Gomis, R., Hanefeld, M., Karasik, A., Laakso, M., “Acarbose for prevention of type 2 diabetes mellitus: the STOP-NIDDM randomised trial”, Lancet., 359 (9323), 2072-2077 (2002). Hong, C., Kim, K.H., Choi, B.T., Choi, G.S., Choi, Y.R., “Process for preparing acarbose with high purity”, U.S. Pat., 6649755 (2003). Rodriguez, J.F., De Lucas, A., Carmona, M., “Application of ion exchange to purify acarbose from fermentation broths”, Biochem. Eng. J., 40, (1), 130-137 (2008). Lange, P.M., Rauenbusch, E., “Polymers for the purification of acarbose”, U.S. Pat., 4666776 (1987). Lange, P.M., Rauenbusch, E., “Process for the purification of acarbose with polymers”, U.S. Pat., 4767850 (1988). Lawton, C., “A process for the purification of acarbose”, WO 99/07720 (1998). Mihaljevic, K., Azaric, J., Bajic, B., “Acarbose purification process”, U.S. Pat., 6734300 (2004). Rauenbusch, E., “Highly pure acarbose”, U.S. Pat., 4904769 (1990). Wang, Y.J., Liu, L.L., Wang, Y.S., “Actinoplanes utahensis ZJB-08196 fed-batch fermentation at elevated osmolality for enhancing acarbose production”, Bioresour. Technol., 103 (1), 337-342 (2012). Wang, Y.J., Liu, L.L., Feng, Z.H., “Optimization of media composition and culture conditions for acarbose production by Actinoplanes utahensis ZJB-08196”, World J. Microbiol. Biotechnol., 27 (12), 2759-2766 (2011). Langmuir, I., “The constitution and fundamental properties of solids and liquids. Part I. solids”, J. Am. Chem. Soc., 38 (11), 2221-2295 (1916). Ho, Y.S., Mckay, G., “A comparison of chemisorption kinetic models applied to pollutant removal on various sorbents”, Process Saf. Environ.

14 15

16

17

18

19

20

21

22 23

24

25

26

27

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Prot., 76 (B4), 332-340 (1998). Ho, Y.S., McKay, G., “Pseudo-second order model for sorption processes”, Process Biochem., 34 (5), 451-465 (1999). Wang, Y.J., Xue, Y.P., Wang, Y.S., “Analysis and determination of anti-diabetes drug acarbose and its structural analogs”, Curr. Pharm. Anal., 7 (1), 12-20 (2011). Catena, G.C., Bright, F.V., “Thermodynamic study on the effects of β-cyclodextrin inclusion with anilinonaphthalene sulfonates”, Anal. Chem., 61 (8), 905-909 (1989). Brucher, J., Bergstrom, L., “Temperature dependence of linuron sorption to three different agricultural soils”, J. Environ. Qual., 26 (5), 1327-1335 (1997). Hall, K.R., Eagleton, L.C., Acrivos, A., “Pore- and solid-diffusion kinetics in fixed-bed adsorption under constant-pattern conditions”, Ind. Eng. Chem. Fundam., 5 (2), 212-223 (1966). Robinson-Lora, M.A., Brennan, R.A., “Biosorption of manganese onto chitin and associated proteins during the treatment of mine impacted water”, Chem. Eng. J., 162 (2), 565-572 (2010). Hamdaoui, O., Saoudi, F., Chiha, M., “Sorption of malachite green by a novel sorbent, dead leaves of plane tree: Equilibrium and kinetic modeling”, Chem. Eng. J., 143, 73-84 (2008). Uslu, H., “Adsorption equilibria of formic acid by weakly basic adsorbent Amberlite IRA-67: Equilibrium, kinetics, thermodynamic”, Chem. Eng. J., 155, 320-325 (2009). Liu, Y., Liu, Y.J., “Biosorption isotherms, kinetics and thermodynamics”, Sep. Purif. Technol., 61 (3), 229-242 (2008). Wawrzkiewicz, M., Hubicki, Z., “Equilibrium and kinetic studies on the adsorption of acidic dye by the gel anion exchanger”, J. Hazard. Mater., 172, 868-874 (2009). Mack, C.L., Wilhelmi, B., Duncan, J.R., “A kinetic study of the recovery of platinum ions from an artificial aqueous solution by immobilized Saccharomyces cerevisiae biomass”, Miner. Eng., 21 (1), 31-37 (2008). Renault, F., Morin-Crini, N., Gimbert, F., “Cationized starch-based material as a new ion-exchanger adsorbent for the removal of C.I. Acid Blue 25 from aqueous solutions”, Bioresour. Technol., 99 (16), 7573-7586 (2008). Yoon, Y.H., Nelson, J.H., “Breakthrough time and adsorption capacity of respirator cartridges”, Am. Ind. Hyg. Assoc. J., 53 (5), 303-316 (1992). Quek, S.Y., Al-Duri, I., “Application of film-pore diffusion model for the adsorption of metal ions on coir in a fixed-bed column”, Chem. Eng. Process., 46 (5), 477-485 (2007). Sivakumar, P., Palanisamy, P.N., “Adsorptive removal of reactive and direct dyes using non-conventional adsorbent-column studies”, J. Sci. Ind. Res., 68 (10), 894-899 (2009).