Recovery of Acetoin from the Ethanol–Acetoin–Acetic Acid Ternary

Article pubs.acs.org/IECR

Recovery of Acetoin from the Ethanol−Acetoin−Acetic Acid Ternary Mixture Based on Adsorption Methodology Using a Hyper-CrossLinked Resin Jinglan Wu,∇,†,‡ Xu Ke,∇,†,‡ Lili Wang,†,‡ Renjie Li,†,‡ Xudong Zhang,†,‡ Pengfei Jiao,†,‡ Wei Zhuang,†,‡ Yong Chen,†,‡ and Hanjie Ying*,†,‡,§ †

College of Biotechnology and Pharmaceutical Engineering, Nanjing University of Technology, Xin mofan Road 5, Nanjing 210009, China ‡ National Engineering Technique Research Center for Biotechnology, Nanjing University of Technology, Nanjing 211816, China § State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology, Nanjing 210009, China ABSTRACT: The separation performances, in terms of adsorption selectivity, desorption, and regeneration of an innovative hyper-cross-linked resin (HD-02) for recovery of acetoin from the ethanol−acetoin−acetic acid ternary mixture were explored in this work. The competitive adsorption behaviors of the ternary mixture were determined experimentally. The results showed the HD-02 resin had a good adsorption selectivity toward acetoin over acetic acid and ethanol. Subsequently, the desorption behaviors in terms of desorption isotherms and kinetics were systematically investigated. Using ethanol as a desorbent, the recovery could be achieved as high as 98% in the batch desorption experiments. The Fick model was adopted to simulate the desorption process. The simulation results revealed that the intraparticle diffusion was the rate-limiting step and the obtained effective diffusivities (1.530 × 10−9 m2/min) were independent of the acetoin concentrations. In the end of this work, three cycles of adsorption−desorption−regeneration operations confirmed good reproducibility of the resin for the attainment of acetoin.

1. INTRODUCTION

In the past few years, we have dedicated ourselves to the development of adsorption methodology to recover butanol from the ABE solution. So far, a weak-polar adsorption resin KA-I12,15 has been selected and proved to have the ability to adsorb butanol, butyric acid, and acetone efficiently, while the residuals (i.e., ethanol, acetic acid, and acetoin, existing in the ABE solution are unrestrained on this type of resin, because of the competitive adsorption effects and remained in the effluent. Hence, after adsorption, the effluent contains almost no butanol, butyric acid, and acetone. In order to realize the coproduction of ABE and acetoin, a new resin must be developed to separate acetoin from ethanol and acetic acid in the effluent. In our previous work, a hyper-cross-linked resin (HD-02) was applied to adsorb pure acetoin. The thermodynamic equilibrium as well as kinetic adsorption of acetoin on the HD-02 resin has been investigated systematically.16 As a continuation of our previous work, the main objective of the present study is to further explore the potential application of the HD-02 resin for recovery of acetoin from the ethanol− acetoin−acetic acid ternary mixture. For this purpose, in addition to the resin adsorption capacity, the adsorption selectivity, desorption and resin regeneration play an essential role in the acetoin recovery process as well. To the best of our knowledge, no previous studies have applied adsorption methodology to separate acetoin from the ABE solution.

Acetoin (3-hydroxy-2-butanone or acetyl methyl carbinol), which is a naturally occurring chemical in the dairy and certain fruits, is widely used to add flavor to food and also serves as a precursor in the synthesis of many important compounds.1,2 This bio-based chemical is defined as one of the high valueadded platform compounds and selected by the U.S. Department of Energy as one of the potential top 30 chemical building blocks from sugars.3 Currently, the industrial production of acetoin via microbial fermentation is a leading method, because of its cost efficiency, compared with the chemical method and enzymatic conversion.4,5 Although some specific microorganisms have the ability to produce acetoin, the long fermentation period that is generally needed hinders its large-scale production.6−8 For many strains, acetoin is only generated as a byproduct.3,9 For instance, the strain C. acetobutylicum B3,10−14 which is widely known as a good producer of acetone−butanol−ethanol (ABE), is able to accumulate acetoin as well. Chen,10 Lin,12 and Liu13 have used this type of strain to perform batch ABE fermentation experiments. Besides the main products, i.e., butanol (∼12 g/L), acetone (∼6 g/L), and ethanol (∼2 g/L), the concentrations of byproducts, i.e., acetic acid, acetoin, and butyric acid in the final fermentation broth are ∼1, 2, and 0.6 g/L, respectively. Traditionally, only ABE were extracted in the separation process, resulting in a loss of total product yield. Since acetoin is a high value-added compound with the price of $41.0/kg, much higher than butanol ($1.75/kg), co-production of ABE and acetoin could be one of the novel alternatives to the ABE production. © 2014 American Chemical Society

Received: Revised: Accepted: Published: 12411

December 26, 2013 July 9, 2014 July 14, 2014 July 14, 2014 dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

solution and 2.0 g of resin. Solutions were prepared in deionized water with acetoin at a known initial concentration (10 g/L). The mixtures were then equilibrated for 24 h at 293 K, with agitation at 120 rpm. After measuring solute concentrations both before and after equilibration, the amounts of adsorbate (i) adsorbed onto resin were calculated by the mass balance relation, as shown in eq 1:17

Accordingly, the following work was carried out in the present study: (i) Screening of six adsorption resins with various polarity and specific surface areas to explore the adsorption mechanism of resins to acetoin. The HD-02 resin showed a great advantage in adsorption capacity and adsorption rate. (ii) Investigation of the competitive adsorption behaviors of the ternary mixture, i.e., ethanol, acetoin, and acetic acid to evaluate the adsorption selectivity of the resin. The feasibility of successful separation of acetoin from the mixture was validated by the experimentally obtained breakthrough curves. (iii) Establishment of a mathematical column model, which takes the axial dispersion and mass transfer into account, for the accurate design of the operating conditions in the sole/multicomponent separation systems. The synthesized ethanol−acetoin−acetic acid solution was used as a feed solution. (iv) Systematic investigation of the acetoin desorption behaviors from the HD-02 resin. The desorption isotherms of acetoin were measured experimentally in various molar ratios of ethanol to water solutions. The kinetics of desorption acetoin on the resin were simulated and the effective diffusivity was obtained. (v) In the end of this work, the adsorption/desorption/ regeneration cycles were carried out to assess the reproducibility of the HD-02 resin.

qi,e =

Kd =

Table 1. Chemical Structures and Physical Properties of the Six Resins matrix structure

KA-I KA-II

PS-PVBa PS-PVBa

KA-III HD-01 HD-02

PS-PVBa PS-PVBa PS-PVBa

weak polarity strong polarity nonpolarity weak polarity weak polarity

HD-03

PS-PVBa

weak polarity

a

pore size distribution

polarity

macropore macropore macropore micropore micropore/ mesopore mesopore

surface area (m2/g)

q (mg/g)

850−900 810

61.81 8.572

845 1646 1294

22.07 73.44 66.55

1129

72.66

m

(1)

where Ci,0 and Ci,e (g/L) are the initial and the equilibrium concentrations of the component, m (g) and V0 (L) represent the weight of the adsorbent and the volume of the solution, qi,e (mg/g wet resin) is the mass of acetoin adsorbed per unit mass of adsorbent at equilibrium. Determination of the adsorption rate was performed using a 500-mL Erlenmeyer flask containing 300 mL of a 10 g/L acetoin solution and 15 g of different resins. The flask was placed in a thermostated water bath with agitation at 120 rpm to maintain the desired temperature (293 K). The samples were withdrawn from the vessel at regular intervals and then analyzed by gas chromatography (GC). Adsorption rate curve (ln(Ct/C0) − t) was applied to investigate the adsorption rate of the six resins. 2.2.2. Batch Adsorption Experiments. Batch adsorption experiments were performed to study the single/multicomponent equilibrium adsorption isotherms onto HD-02 resin at the temperature of 293 K. The concentration ratio of ethanol:acetoin:acetic acid in ternary mixture solution was equal to 2:2:1, which was close to the ratio of these components in the actual final fermentation broth.10,13 The experiments with the same laboratory equipment and procedures as the method described in section 2.2.1 were repeated. The amount of single/multicomponent adsorbed per unit mass of resin (qi,e) and distribution coefficient (Kd)18,19 were calculated by eqs 1 and 2, respectively:

2. MATERIALS AND METHODS 2.1. Materials. Pure 99% acetoin was purchased from Sigma−Aldrich. Ethanol and acetic acid (>99.5 wt %) were obtained from Sinopharm Chemical Reagent Co., Ltd. The six adsorbents used in this research were kindly provided by National Engineering Technique Research Center for Biotechnology (Nanjing, China). The chemical structures and physical properties of the resins are listed in Table 1. Prior to

type of resin

(C i,0 − C i,e)V0

1000V0(C i,0 − C i,e) mC i,e

(2)

2.2.3. Fixed-Bed Experiments. Fixed-bed adsorption runs were carried out in glass columns with an inside diameter of 1.90 cm and a length of 30 cm. Every column had a water jacket to maintain the desired constant operating temperature (293 K). Solutions with a known concentration were fed to the top of the column at different flow rates regulated by a constantspeed pump. The effluent samples were collected at intervals and analyzed via GC. In fixed-bed studies, the adsorption performance of a column is mostly evaluated by analyzing the form of normalized concentration, Cout/CF of the effluent vs time curves (i.e., breakthrough curves). 2.2.4. Batch Desorption Experiments. The desorption equilibrium experiments were performed in 100-mL Erlenmeyer flasks that contain 2 g of resin and 50 mL of acetoin− ethanol−water solution with different molar ratios of ethanol to water (i.e., 0:1 to 1:0). The procedures described in section 2.2.1 then were repeated and the adsorption capacities (mg/g) of acetoin in the mixture solutions were calculated using eq 1. The desorption kinetics experiments were conducted immediately after the adsorption experiments using acetoinloaded adsorbent, which was previously exposed to different concentrations (initial concentration from 4.675 g/L to 24.82 g/L) of acetoin solution. After the attainment of adsorption

Polystyrene−poly(vinyl)-benzene.

the adsorption experiments, the resins were pretreated first by soaking it into the ethanol solution for 24 h and then by 1 M HCl and 1 M NaOH for 8 h to remove preservative agents and polymerization residuals. Finally, the resins were washed to neutral pH with deionized water. 2.2. Methods. 2.2.1. Preliminary Selection of the Proper Resin for Adsorption of Acetoin. The batch static method was used for determination of the adsorption capacities of different resins. Equilibrium adsorption experiments were carried out in closed 100-mL Erlenmeyer flasks containing 50 mL of aqueous 12412

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

3.2. Adsorption Selectivity. The separation factor23−25 (∂i/i′), which is an index of selectivity, was defined as the ratio of distribution coefficient (Kd) of component i to component i′. The separation factor values of ∂AAc, ∂AE , ∂EAc were used to evaluate the resin selectivity of acetoin/acetic acid, acetoin/ ethanol, and ethanol/acetic acid, respectively. 3.3. Mathematical Modeling of a Single Chromatographic Column. The fixed-bed column model is the core for design and optimization of the operating conditions in the sole/multicomponent separation systems. The transport dispersive model (TDM),26−28 which takes into account the axial dispersion as well as the mass-transfer resistance in the solid phase, was considered to simulate the experimentally attained breakthrough curves of the single component (acetoin) and the ternary mixture (acetoin, ethanol, and acetic acid). The overall mass balance in the mobile phase is29

equilibrium, the adsorbed resin was washed with distilled water and then dried by filter paper. The following operation was carried out in a 250-mL Erlenmeyer flask that contained 200 mL of absolute ethanol and 5 g of saturated resin. The flask was placed in a thermostated water bath to maintain the desired temperature (293 K). The agitation was fixed to 120 rpm to ensure that the film mass-transfer effects caused by the low agitation speed were neglected. Samples were withdrawn at different times with a syringe, and then measured by GC. The percentage desorption of acetoin (D%) from acetoin-loaded adsorbent was calculated using eq 3: D% =

CxVx (C0 − Ce)V0

(3)

where Cx (g/L) is the concentration of acetoin in the elution and Vx (L) is the volume of elution. 2.2.5. Regeneration Experiments. After fixed-bed adsorption experiments, the acetoin was eluted from the loaded adsorbent by the desorbent. All effluent samples were collected by a fraction collector at definite intervals and measured by GC. Then, the HD-02 resin was washed with deionized water and used again in the next cycle. Acetoin was used to saturate the loaded adsorbent with a flow rate of 3.0 mL/min previously, the elution and regeneration rate flow were 1.5 mL/min and 3.0 mL/min, respectively. The recycling studies of adsorption/ desorption/regeneration were repeated for three times in order to examine the resin reproducibility. 2.2.6. Analytical Method. The ethanol, acetoin, and acetic acid concentration were determined via gas chromatography (GC) (Model 7890A, Agilent, USA) equipped with a 60 m × 0.25 mm × 0.25 μm Agilent HP-INNOWAX 19091N-236 column. The oven temperature program used was as follows: 70 °C for 0.5 min and then increased to 190 °C at 20 °C/min (6 min) for 1 min. The carrier gas was nitrogen, which had a flow rate of 2 mL/min. The injector temperature was 180 °C, and the FID detector temperature was 220 °C. The split ratio was set to be 1/90.

∂ci ∂c ∂ 2c 1 − ε ∂qi +v i +ρ = Di,L 2i ∂t ∂z ε ∂t ∂z

wherev (mL/min) is the interstitial velocity, z (cm) and ρ (g/ mL) are the axial coordinate of the column and the resin bed density, t (min) is the time, ε (ε = 0.45) is the bed porosity and ci (g/L) represents the concentration of the component i in the bulk liquid phase. DL (m2/min) denotes the axial dispersion coefficient and can be obtained using following correlation suggested by Suzuki and Smith:30 Di,L = 0.44Di,m + 0.83ud p

Di,m = 7.4 × 10−8

∂qi ∂t

(4)

(8)

= keff (qi,e − qi)

at t = 0:

(9)

ci(t , z) = 0, qi(t , z) = 0

The boundary conditions expressions:

aiCi , j n

1 + ∑ j = 1 bjCi , j

ηBV A0.6

where keff (m/min) is the mass-transfer coefficient, which is obtained by the best fitting of the simulation results to the experimental data. The initial conditions are written as follows,

where qm is the Langmuir isotherm constant (mg/g wet resin) and K is the equilibrium coefficient (L/g). In the multicomponent systems, the adsorption capacity of each solute at equilibrium depends on the concentration of other components present locally.21 As a result, the competitive Langmuir isotherm model was used to describe the adsorption equilibrium of each solute as follows:22 qi , j =

ϕMB T

where VA (cm3) is the molar volume of the liquid solute at its normal boiling point, MB (g) is the molecular weight of the solvent, ηB(N S m−2) its viscosity, and φ is a constant which accounts for solute−solvent interactions and has a recommended value of 2.6 for water. The differential mass balance equation in the solid phase32 is given by

qi,mK iC i,e 1 + K iC i,e

(7)

where dp (cm) is the particle diameter, u (cm/min) the superficial velocity, and Dm (m2/min) the molecular coefficient, which can be calculated as31

3. THEORY 3.1. Single/Multicomponent Adsorption Equilibrium. In the single-component system, the experimental equilibrium data of each individual solute were fitted by the Langmuir isotherm model,20 which is represented as follows: qi,e =

(6)

33

are written from the following

at z = 0: ∂C (t , z = 0) DL i = vCi ,0(t ) − vCi(t , z = 0) ∂z

(5)

where a and b are the equilibrium coefficients (L/g), the constants a (a = qmax × KL) and b (b = KL) in the competitive Langmuir isotherm model are dependent on the equilibrium concentrations of other components and are not independent; j and n are the number of components.

at z = L : 12413

(10)

∂Ci(t , z = L) =0 ∂z

(11)

(12)

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

where L (cm) is the length of the fixed bed. Adsorption equilibrium isotherms of species i in the single/ multicomponent systems (qi,e = f(ci)) can be described by the Langmuir isotherm (eq 4) or the competitive Langmuir isotherm model (eq 5). The partial differential equations were solved efficiently in MATLAB 2010a. After the discretization step, the time integration is performed by the ordinary differential equation solver ODE23. An absolute and relative tolerance of 10−5 was used. 3.4. Desorption Kinetics Model. The Fick model34,35 was applied to predict the acetoin desorption process on the HD-02 resin. The model was simplified by making the following assumptions: (i) the resin was treated as a quasi-homogeneous phase; (ii) diffusion was restricted to radial diffusion; and (iii) intraparticle diffusion was the rate-limiting step throughout the process. Accordingly, the conservation equations for acetoin in the bulk fluid and in the particles include V

dC m 3 ∂q =− De ρ R ∂r dt

KA-II, while the strong polarity resin KA-III shows practically no adsorption to acetoin. It indicates that, irrespective of their nature, the polymer resins that possess hydrophobic surface chemistries (to support stronger surface interactions through van der Waals forces) as well as high specific surface areas might serve as effective adsorbents for the separation of acetoin from the aqueous solutions. Meanwhile, the adsorption rates for the six adsorbents have been determined experimentally and the results were presented with adsorption rate curves (ln(Ct/ C0) − t) in Figure 1. As can be seen, all of the acetoin

(13)

r=R

⎛ ∂ 2q ∂q 2 ∂q ⎞ ⎟ = De⎜ 2 + ∂t r ∂r ⎠ ⎝ ∂r

(14)

3

where V (cm ) is the volume of adsorbent, R (cm) is the radial distance from the center of the pellet, and De (m2/min) represents the effective diffusion coefficient, which was estimated by matching the experimental concentration decay data (cexp, g/L), with the concentration decay predicted with a numerical solution of the diffusion model (ccal, g/L). The best value for De was obtained when the diffusion model best-fit the experimental data, considering that the optimum fit was achieved by minimizing the following objective function:36 ⎛ ce − ccal ⎞2 minimum = ∑ ⎜ ⎟ ce ⎠ i=1 ⎝

Figure 1. Adsorption rate curves of the six different resins to acetoin at the temperature of 293 K (C0 = 10 g/L).

adsorption attain equilibrium within 30 min; the six adsorbents possess almost the same adsorption rate. All the HD series resin can be used for the recovery of acetoin. As shown in Table 1, we can see that the HD-01 resin possesses a uniform micropore structure while the HD-02 resin has both micropores and mesopores, which means the pore distribution is much wider than that of HD-01. Therefore, it is more complicated to synthesize the HD-01 resin, resulting in the high cost of producing the HD-01 resin. Proceeding from the economic point of view, the HD-01 resin would be inappropriately used in the industrial application. Since the HD-02 resin presents relatively high adsorption capacity, as well as a high adsorption rate to acetoin, and the resin has been used to adsorb acetoin in our previous work, this resin is selected preliminarily as the proper resin for adsorption of acetoin and used in the following work. 4.2. Single/Multicomponent Adsorption Equilibrium. For the sake of comparison, the single-component and multicomponent adsorption isotherms, in terms of ethanol, acetoin, and acetic acid, on the HD-02 resin at a temperature of 298.15 K are presented in Figure 2. The acetoin concentrations ranged from 0 to 30.0 g/L. According to the composition in the real ABE fermentation broth (i.e., ethanol:acetoin:acetic acid = 2:2:1), in the multicomponent system, the ethanol concentrations were set to be 0 to 30.0 g/L and those of acetic acid to be 0 to 15.0 g/L. The Langmuir isotherm (eq 4) and the competitive Langmuir isotherm models (eq 5), which describe the single-component and multicomponent adsorption behaviors, were used to fit the adsorption isotherm data. The fitting results also are shown in Figure 2. Good agreements between the model predictions and the experimental data can be observed. The model parameters are listed in Table 2.

N

(15)

Meanwhile, the average relative deviation (ARD%, as defined by eq 16) is used to evaluate the model fitness as well: ARD% =

1 N

N

∑ i=1

cexp − ccal cexp

× 100 (16)

where the subscripts “exp” and “cal” denote the experimental and calculated values, respectively, and N is the number of experimental data points.

4. RESULTS AND DISCUSSION 4.1. Preliminary Selection of the Proper Resin for Adsorption of Acetoin from Aqueous Solution. Six different types of resins were screened for their ability to take-up acetoin from the aqueous solution with an initial concentration of 10 g/L, in which the series of KA resins were the macropore adsorption polymers with various polarities, whereas the series of HD resins were hyper-cross-linked polymers with the specific surface areas all above 1000 m2/g (see our previous work in ref 16). The adsorption capacities of these resins to acetoin are compared in Table 1. It can be observed that HD series resins generally display higher affinity to acetoin, because of the large specific surface areas and the uniform micropore/mesopore structures that supply better compatibility with the adsorbate acetoin. The uptake of weak polarity resin KA-I is higher than that of the nonpolarity resin 12414

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

Figure 2. Adsorption isotherms of ethanol, acetoin, and acetic acid onto HD-02 resin in single-component and ternary systems at a temperature of 293 K.

Figure 3. Separation factors of the ternary system, in terms of the amounts of ethanol, acetion, and acetic acid, at a temperature of 293 K.

Table 2. Isotherm Parameters for Solutes Adsorption on HD-02 Resin single component

demonstrating that these two substances can be easily separated by the HD-02 resin. The average value of ∂AAc is ∼1.5, indicating that these two substances can also achieve baseline separation. However, the separation of acetic acid from ethanol is not easy, because of the small value of ∂EAc, i.e., ∼1.0. Anyway, the main objective of this study is to recover acetoin, according to the values of ∂AE and ∂AAc, we can conclude that the selected novel HD-02 resin possesses a good adsorption selectivity toward acetoin over acetic acid and ethanol. 4.4. Mathematical Modeling of the Column Adsorption Process for the Sole and Ternary Mixture Systems. In principle, purification and recovery of acetoin from the ABE fermentation broth would be realized on the chromatographic column in the end. Consequently, investigation of the breakthrough curves, especially the competitive breakthrough curves that are used to evaluate the simultaneous adsorption behavior and species interactions, are of great importance. In this section, the breakthrough curves of the single component, with regard to acetoin, acetic acid, and ethanol, as well as their competitive breakthrough curves were experimentally recorded and simulated by means of the TDM model. The corresponding results are presented in Figure 4. The model predictions fit the experimental data fairly well. Since the adsorption affinities of ethanol and acetic acid on the HD-02 resin are weak, the packed-column is soon saturated with these solutes. Acetoin shows the strongest adsorption affinity to the resin, which is consistent with the results obtained from the single-component equilibrium data (Figure 2). For the ternary system, the breakthrough time of each component is ahead of their individual pure component, indicating that the adsorption capacities are reduced. It also corresponds to the results obtained from the ternary-component equilibrium data (Figure 2). Moreover, the overshoots for ethanol and acetic acid concentrations (Cout/CF) can be observed in Figure 4. This is because the least-adsorbed substance ethanol was displaced and desorbed simultaneously by the middle adsorbed one (acetic acid), whereas the most adsorbed component (acetoin) replaced acetic acid as well. According to Moreira and Ferreira,37 the overshoot phenomena in adsorption multicomponent systems as a result of the competition for active sites on the resin can be predicted by the equilibrium theory and considering the column divided into zones of unique

multicomponent

solute

qm(mg/g)

KL(L/g)

R2

a(L/g)

b(L/g)

ethanol acetoin acetic acid

209.5 228.3 192.3

0.0192 0.0748 0.0347

0.9942 0.9983 0.9943

4.551 10.36 6.516

0.0037 0.0581 0.0010

It is clear that, in the single-component system, acetoin, acetic acid, and ethanol can be all retained on the HD-02 resin. The relative adsorption affinity of these three compounds to the HD-02 resin follows the order: acetoin > acetic acid > ethanol. However, in the multicomponent system, the adsorption capacity is reduced significantly, in comparison with its individual pure component. For instance, the uptake of acetoin is reduced from 228.31 mg/g to 178.43 mg/g. At the same time, with the coexistence of acetoin, the uptakes of ethanol and acetic acid on the HD-02 resin are also reduced greatly, indicating that the competition adsorption occurs among these components. This phenomenon would be further verified in the multicomponent competitive breakthrough curves in section 4.4. Nevertheless, no matter either in the single-component or in the multicomponent system, acetoin always displays stronger affinity to the resin than acetic acid and ethanol, which implies the selected HD-02 resin possesses good adsorption selectivity toward acetoin. Hence, the separation factors of acetoin/acetic acid, acetoin/ethanol, and acetic acid/ ethanol would be calculated to prove the resin selectivity quantitatively. 4.3. Adsorption Selectivity of HD-02 Resin. The separation factor was calculated according to section 3.2, to evaluate whether the HD-02 resin could be applicable for the selective adsorption toward acetoin from a multicomponent system. The obtained separation factors of acetoin/acetic acid, acetoin/ethanol, and acetic acid/ethanol are presented in Figure 3. At a fixed initial concentration ratio of ethanol, acetoin, and acetic acid (2:2:1), the separation factors varied in the range of 2.122 < ∂AE < 2.670, 1.387 < ∂AAc < 1.906, 0.7987 < E ∂Ac < 1.1719. Since acetoin is the strongest retained component, while ethanol is the weakest retained one, the separation factor ∂AE shows the maximum value of above 2, 12415

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

Figure 4. Breakthrough curves of ethanol, acetoin, and acetic acid onto HD-02 resin in single-component and ternary systems at a temperature of 293 K.

Figure 5. Desorption isotherms of acetoin in different molar ratios of ethanol and water at T = 293 K.

Table 3. Coefficients of the Desorption Isotherms at Different Molar Ratios of Ethanol and Water, T = 293 K

compositions, called plateaus, separated from each other by zones of varying compositions, called transitions. The peaks in the concentrations during the breakthrough of ethanol and acetic acid occur at times of 96 and 107 min, respectively. The stoichiometric time for acetoin is 130 min. The time interval between the overshoots of ethanol and acetic acid and the stoichiometric point of acetoin indicates a good separation can be achieved. Because of the good agreement between the experimentally obtained breakthrough curves and the model predictions, the adsorption equilibriums, as well as the TDM model proposed in this work, can be considered correct. 4.5. Product Recovery and Resin Regeneration. The operating steps, in terms of desorption and regeneration, plays an important role in a complete acetoin recovery process. However, most of the literature has focused on the adsorption process.16,38,39 Relatively limited information is available on desorption behavior and resin regeneration. Accordingly, in this section, the desorption equilibrium isotherms and the desorption kinetics of acetoin on the HD-02 resin were determined experimentally and simulated. The adsorption− desorption-regeneration cycles were carried out to access the reproducibility of the resin. 4.5.1. Desorption Equilibrium Isotherm. Selection of a proper desorbent is of primary importance in the desorption process. Generally, the following factors would be taken into account for choosing a suitable desorbent:12,40 (i) high solubility of the adsorbate(s) in the desorbent, (ii) easy separation of the adsorbate(s) from the desorbent, and (iii) enrichment of the adsorbate(s) in the eluent, if possible. In the case of acetoin recovery, pure ethanol was chosen to be a desorbent. Besides fulfillment of the above-mentioned requirements, another important reason to select ethanol as a desorbent is that it is already existed in the butanol fermentation broth. Therefore, taking advantage of ethanol can avoid the introduction of additional impurities into the complete separation process. The desorption isotherms of acetoin at different molar ratios of ethanol and water solutions are shown in Figure 5. The Langmuir isotherm model was used to fit the experimental data. The resulting parameters (i.e., the maximum adsorption capacity (qmax) and the Langmuir constant (k)) are listed in Table 3. As can be seen, qmax and k decrease as the ethanol

nethanol:nwater

K

qmax

R2

1:0 1:7 1:11 1:19 1:50 1:150 1:250 0:1

0.0102 0.0210 0.0213 0.0265 0.0336 0.0551 0.0616 0.0748

58.71 83.49 96.84 110.5 125.5 154.2 168.0 228.3

0.9937 0.9968 0.9989 0.9930 0.9942 0.9982 0.9987 0.9949

concentration increases. It seems that the solution composition has a strong influence on the retention behavior of acetoin on the HD-02 resin. As a matter of fact, this phenomenon is wellknown in analytical chromatography, in that changing the mobile phase composition (e.g., either changing the ratio between a polar and an apolar solvent, or changing the pH of the solution) significantly modifies the solute adsorptivity on the stationary phase.41 As competitive adsorption presents between acetoin and ethanol, it is reasonable to assume that the desorption of acetoin from the resin could be a result of competing interactions between the intermolecular forces of adsorption on the resin and dissolution in the solvent. When intermolecular forces are recessive, acetoin desorbs from the resin into the solvent. Therefore, a high ethanol concentration would decrease the intermolecular forces of acetoin and the resin, resulting in a reduction of adsorption capacity. 4.5.2. Modeling the Desorption Kinetics. Batch desorption experiments of loaded acetoin on the HD-02 resin were carried out to study the desorption kinetics. The concentration decay curves of acetoin with various initial concentrations were recorded experimentally and are presented in Figure 6. The fitting lines were calculated by the Fick model. Good agreement between the experimental data and the predictions can be observed. The desorption process is found to be faster than adsorption, because the desorption rate is rapid for the first 10 min and thereafter it proceeds at a slower rate and finally attains the desorption equilibrium within ∼16 min, while in the adsorption step, the equilibrium time was over 30 min (see our previous work in ref 16). Since 200 mL of pure ethanol was used to desorb 5 g of saturated resin in the desorption 12416

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

Figure 7. Three adsorption/desorption/regenaration cycles of acetoin onto the HD-02 resin (T = 293 K).

Figure 6. Desorption kinetics of acetoin at different initial concentrations when T = 293 K.

experiments, the desorption recovery could be calculated to be as high as 98%. It confirms that ethanol could be a suitable desorbent to elute acetoin from the resin. The effective diffusivities De in the Fick model obtained by the best-fitting of the experimental data are given in Table 4. It can be seen that

good adsorbent that can be used successfully in the acetoin recovery process. After regeneration steps, the residual components in the effluent are ethanol, acetoin, and water. Since an azeotrope can be formed between ethanol and water, the difference between the boiling points of acetoin and the azeotrope is therefore enhanced. The commonly used distillation method can then be applied to obtain acetoin from ethanol−water solution and it will be discussed and detailed in the future work.

Table 4. Coefficients of the Desorption Kinetic Model at Different Initial Concentrations, T = 293 K C0 (g/L)

Ce (g/L)

4.675 10.22 14.44 24.82

0.9987 1.443 2.240 2.506

De (× 10−9 m2 min−1) 1.530

desorption rate (%)

ARD%

98.26 98.55 98.40 98.74

7.368 6.507 4.071 7.297

5. CONCLUSIONS Six adsorption resins with various polarity and specific surface areas were screened to explore the adsorption mechanism to acetoin. The weak-polarity HD-02 resin showed excellent adsorption properties for acetoin. The adsorption selectivity, desorption equilibrium isotherms and kinetics, as well as regeneration studies were investigated systematically to evaluate the feasibility of successful separation of acetoin from the ternary mixture, in terms of ethanol, acetoin, and acetic acid. The results revealed that the affinity of these three compounds to the HD-02 resin follows the order: acetoin > acetic acid > ethanol. The obtained effective diffusivity De (1.530 × 10−9 m2/ min) was independent of the acetoin concentrations, indicating that the radial diffusion was the rate-limiting step throughout the desorption process. These preliminary experiments suggested that the adsorption of acetoin by the HD-02 resin could be an attractive method to separate acetoin from the ethanol−acetoin−acetic acid ternary system, and could be particularly useful for realizing the co-production of acetone− butanol−ethanol (ABE) and acetoin in the future.

the values are independent of the acetoin concentrations. Since acetoin is almost not retained on the resin, the diffusion is restricted to the radial diffusion and is the rate-limiting step throughout the desorption process.42 4.5.3. Resin Regeneration. The adsorption−desorptionregeneration steps were carried out in the chromatographic column to assess the reproducibility of the HD-02 resin. The experimentally attained adsorption breakthrough curves, as well as the elution curves of acetoin, are depicted in Figure 7. The fix-column bed was saturated with 5.011 g/L acetoin solution of ∼8.11 BV (bed volume) and then the acetoin recovery attained values as high as 98.7% when eluted by 2.45 BV pure ethanol. Consequently, the acetoin concentration would be enriched in the elution. As can be seen in Figure 7, the concentration of acetoin at the peak of the elution curve could achieved values as high as 77.67 g/L, ∼15.5 times higher than the feed concentration. However, comparison of the total bed volume used for adsorption with that used for desorption, acetoin was only concentrated 3.31 times after the adsorption and desorption process. The HD-02 resin was immersed in the ethanol solution after the elution process. Since ethanol and water are miscible with each other, the best regenerant would be water. The optimal amount of water to complete regeneration of the resin was obtained experimentally of 3.2 BV. After three adsorption−desorption−regeneration cycles, the adsorption capacity of resin to acetoin remains unchangeable. The results confirm that the HD-02 resin is a potential

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86 25 86990001. Fax: +86 25 58139389. E-mail: [email protected]. Author Contributions ∇

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest. 12417

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

■

Article

several pressures and temperatures. Fluid Phase Equilib. 2013, 356, 102−108. (3) Ji, X.-J.; Xia, Z.-F.; Fu, N.-H.; Nie, Z.-K.; Shen, M.-Q.; Tian, Q.Q.; Huang, H. Cofactor engineering through heterologous expression of an NADH oxidase and its impact on metabolic flux redistribution in Klebsiella pneumoniae. Biotechnol. Biofuels 2013, 6 (1), 7. (4) Zhang, Y.; Li, S.; Liu, L.; Wu, J. Acetoin production enhanced by manipulating carbon flux in a newly isolated Bacillus amyloliquefaciens. Bioresour. Technol. 2013, 130, 256−260. (5) Cho, S.; Kim, K. D.; Ahn, J.-H.; Lee, J.; Kim, S.-W.; Um, Y. Selective Production of 2,3-Butanediol and Acetoin by a Newly Isolated Bacterium Klebsiella oxytoca M1. Appl. Biochem. Biotechnol. 2013, 1−12. (6) Fan, Y.; Tian, Y.; Zhao, X.; Zhang, J.; Liu, J. Isolation of AcetoinProducing Bacillus Strains from Japanese Traditional FoodNatto. Preparative Biochem. Biotechnol. 2013, 43 (6), 551−564. (7) Xu, H.; Jia, S.; Liu, J. Development of a mutant strain of Bacillus subtilis showing enhanced production of acetoin. Afr. J. Biotechnol 2011, 10 (5), 779−788. (8) Liu, Y.; Zhang, S.; Yong, Y.-C.; Ji, Z.; Ma, X.; Xu, Z.; Chen, S. Efficient production of acetoin by the newly isolated Bacillus licheniformis strain MEL09. Process Biochem. 2011, 46 (1), 390−394. (9) Wu, Z.; Wang, Z.; Wang, G.; Tan, T. Improved 1,3-propanediol production by engineering the 2,3-butanediol and formic acid pathways in integrative recombinant Klebsiella pneumoniae. J. Biotechnol. 2013, 168 (2), 194−200. (10) Chen, Y.; Zhou, T.; Liu, D.; Li, A.; Xu, S.; Liu, Q.; Li, B.; Ying, H. Production of butanol from glucose and xylose with immobilized cells of Clostridium acetobutylicum. Biotechnol. Bioprocess. Eng. 2013, 18 (2), 234−241. (11) Doremus, M. G.; Linden, J. C.; Moreira, A. R. Agitation and pressure effects on acetone−butanol fermentation. Biotechnol. Bioeng. 1985, 27 (6), 852−860. (12) Lin, X.; Wu, J.; Jin, X.; Fan, J.; Li, R.; Wen, Q.; Qian, W.; Liu, D.; Chen, X.; Chen, Y. Selective separation of biobutanol from acetone−butanol−ethanol fermentation broth by means of sorption methodology based on a novel macroporous resin. Biotechnol. Progress 2012, 28 (4), 962−972. (13) Liu, D.; Chen, Y.; Li, A.; Ding, F.; Zhou, T.; He, Y.; Li, B.; Niu, H.; Lin, X.; Xie, J.; Chen, X.; Wu, J.; Ying, H. Enhanced butanol production by modulation of electron flow in Clostridium acetobutylicum B3 immobilized by surface adsorption. Bioresour. Technol. 2013, 129, 321−328. (14) Siemerink, M. A.; Kuit, W.; Contreras, A. M. L.; Eggink, G.; van der Oost, J.; Kengen, S. W. D-2,3-butanediol production due to heterologous expression of an acetoin reductase in Clostridium acetobutylicum. Appl. Environ. Microbiol. 2011, 77 (8), 2582−2588. (15) Lin, X.; Li, R.; Wen, Q.; Wu, J.; Fan, J.; Jin, X.; Qian, W.; Liu, D.; Chen, X.; Chen, Y. Experimental and modeling studies on the sorption breakthrough behaviors of butanol from aqueous solution in a fixed-bed of KA-I resin. Biotechnol. Bioprocess Eng. 2013, 18 (2), 223− 233. (16) Wu, J.; Wang, L.; Zhou, J.; Zhang, X.; Liu, Y.; Zhao, X.; Wu, J.; Zhuang, W.; Xie, J.; He, X.; Ying, H. Recovery of acetoin from the aqueous solution by means of a novel hyper-cross-linked resin: Equilibrium and kinetics. J. Food Eng. 2013, 119 (4), 714−723. (17) Su, H.; Wang, Z.; Tan, T. Adsorption of Ni2+ on the surface of molecularly imprinted adsorbent from Penicillium chysogenum mycelium. Biotechnol. Lett. 2003, 25 (12), 949−953. (18) Muslu, N.; Gülfen, M. Selective separation and concentration of Pd(II) from Fe(III), Co(II), Ni(II), and Cu(II) ions using thiourea− formaldehyde resin. J. Appl. Polym. Sci. 2011, 120 (6), 3316−3324. (19) Long, K. M.; Goff, G. S.; Ware, S. D.; Jarvinen, G. D.; Runde, W. H. Anion Exchange Resins for the Selective Separation of Technetium from Uranium in Carbonate Solutions. Ind. Eng. Chem. Res. 2012, 51 (31), 10445−10450. (20) Langmuir, I. The Constitution and Fundamental Properties of Solids and Liquids. Part I. Solids. J. Am. Chem. Soc. 1916, 38 (11), 2221−2295.

ACKNOWLEDGMENTS This work was partly supported by a grant from the National Outstanding Youth Foundation of China (Grant No. 21025625), the PCSIRT, and the PAPD. We would also like to acknowledge the financial support provided by the National High-Tech Research and Development Plan of China (863 Program, No. 2012AA021202) and by the State Key Laboratory of Motor Vehicle Biofuel Technology.

■

NOMENCLATURE a, b = multicomponent competitive Langmuir isotherm constants, L/g C = concentration of liquid phase, g/L cal = calculated value dp = particle diameter, cm D% = percentage desorption of acetoin from an acetoinloaded adsorbent De = effective diffusion coefficient, m2/min DL = axial dispersion coefficient, m2/min DM = molecular coefficient, m2/min e = equilibrium condition exp = experimental value i = sorbate species i j = all sorbate species k = single-component Langmuir isotherm constant related to the rate of adsorption, L/g keff = mass-transfer coefficient, m/min kd = distribution coefficient, L/g L = length of fixed bed, cm m = mass of wet resin, g MB = molecular weight of the solvent, g n = number of components in the system N = number of experimental data points out = effluent solution q = adsorption capacity, mg/g r = radius of a resin particle, cm R = radial distance from the center of the pellet, cm t = time, min T = temperature, K v = interstitial velocity, mL/min V = volume of adsorbent, cm3 V0 = volume of aqueous solution, L VA = molar volume of the liquid solute at its normal boiling point, cm3 x = acetoin in the elution z = axial coordinate of the column, cm 0 = initial condition α = separation factor ρ = resin bed density, g/mL ε = bed porosity (ε = 0.45) u = superficial velocity, cm/min φ = constant that accounts for solute−solvent interactions; the recommended value is 2.6 for water ηB = solvent viscosity, N S m−2

■

REFERENCES

(1) Zhang, X.; Zhang, R.; Bao, T.; Yang, T.; Xu, M.; Li, H.; Xu, Z.; Rao, Z. Moderate expression of the transcriptional regulator ALsR enhances acetoin production by Bacillus subtilis. J. Ind. Microbiol. Biotechnol. 2013, 40 (9), 1067−1076. (2) Effendi, C.; Shanty, M.; Ju, Y.-H.; Kurniawan, A.; Wang, M.-J.; Indraswati, N.; Ismadji, S. Measurement and mathematical modeling of solubility of buttery-odor substance (acetoin) in supercritical CO2 at 12418

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419

Industrial & Engineering Chemistry Research

Article

(21) Zhou, J.; Wu, J.; Liu, Y.; Zou, F.; Wu, J.; Li, K.; Chen, Y.; Xie, J.; Ying, H. Modeling of breakthrough curves of single and quaternary mixtures of ethanol, glucose, glycerol and acetic acid adsorption onto a microporous hyper-cross-linked resin. Bioresour. Technol. 2013, 143, 360−368. (22) Shirazi, D. G.; Felinger, A.; Katti, A. M. Fundamentals of Preparative and Nonlinear Chromatography; Academic Press: New York, 2006. (23) Li, L.; Liu, F.; Jing, X.; Ling, P.; Li, A. Displacement mechanism of binary competitive adsorption for aqueous divalent metal ions onto a novel IDA-chelating resin: Isotherm and kinetic modeling. Water Res. 2011, 45 (3), 1177−1188. (24) Li, B.; Liu, F.; Wang, J.; Ling, C.; Li, L.; Hou, P.; Li, A.; Bai, Z. Efficient separation and high selectivity for nickel from cobalt-solution by a novel chelating resin: Batch, column and competition investigation. Chem. Eng. J. 2012, 195, 31−39. (25) Wu, X.; Arellano-Garcia, H.; Hong, W.; Wozny, G. n. Improving the Operating Conditions of Gradient Ion-Exchange Simulated Moving Bed for Protein Separation. Ind. Eng. Chem. Res. 2013, 52 (15), 5407−5417. (26) Lv, L.; Zhang, Y.; Wang, K.; Ray, A. K.; Zhao, X. S. Modeling of the adsorption breakthrough behaviors of Pb2+ in a fixed bed of ETS10 adsorbent. J. Colloid Interface Sci. 2008, 325 (1), 57−63. (27) Ströhlein, G.; Aumann, L.; Mazzotti, M.; Morbidelli, M. A continuous, counter-current multi-column chromatographic process incorporating modifier gradients for ternary separations. J. Chromatogr. A 2006, 1126 (1), 338−346. (28) Schmidt-Traub, H. In Preparative Chromatography of Fine Chemicals and Pharmaceutical Agents; Wiley−VCH Verlag: Weinheim, Germany, 2005. (29) Schmidt-Traub, H.; Schulte, M.; Seidel-Morgenstern, A. Preparative Chromatography; John Wiley & Sons: New York, 2012. (30) Suzuki, M.; Smith, J. Axial dispersion in beds of small particles. Chem. Eng. J. 1972, 3, 256−264. (31) Wilke, C.; Chang, P. Correlation of diffusion coefficients in dilute solutions. AIChE J. 1955, 1 (2), 264−270. (32) Glueckauf, E. Theory of chromatography. Part 10.Formulae for diffusion into spheres and their application to chromatography. Trans. Faraday Soc. 1955, 51, 1540−1551. (33) Danckwerts, P. Continuous flow systems: distribution of residence times. Chem. Eng. Sci. 1953, 2 (1), 1−13. (34) Li, X.; Zhang, L.; Chang, Y.; Shen, S.; Ying, H.; Ouyang, P. Kinetics of adsorption of thymopentin on a gel-type strong cationexchange resin. Chromatographia 2007, 66 (3−4), 231−235. (35) Cayan, F. N.; Pakalapati, S. R.; Elizalde-Blancas, F.; Celik, I. On modeling multi-component diffusion inside the porous anode of solid oxide fuel cells using Fick’s model. J. Power Sources 2009, 192 (2), 467−474. (36) Zhou, X.; Fan, J.; Li, N.; Qian, W.; Lin, X.; Wu, J.; Xiong, J.; Bai, J.; Ying, H. Adsorption Thermodynamics and Kinetics of Uridine 5′Monophosphate on a Gel-Type Anion Exchange Resin. Ind. Eng. Chem. Res. 2011, 50 (15), 9270−9279. (37) Moreira, M. J. A.; Gando-Ferreira, L. M. Separation of phenylalanine and tyrosine by ion-exchange using a strong-base anionic resin. I. Breakthrough curves analysis. Biochem. Eng. J. 2012, 67, 231−240. (38) Forlani, G.; Mantelli, M.; Nielsen, E. Biochemical evidence for multiple acetoin-forming enzymes in cultured plant cells. Phytochemistry 1999, 50 (2), 255−262. (39) Speckman, R.; Collins, E. Separation of diacetyl, acetoin, and 2,3-butylene glycol by salting-out chromatography. Anal. Biochem. 1968, 22 (1), 154−160. (40) Faria, R. P.; Pereira, C. S.; Silva, V. M.; Loureiro, J. M.; Rodrigues, A. E. Glycerol valorisation as biofuels: Selection of a suitable solvent for an innovative process for the synthesis of GEA. Chem. Eng. J. 2013, 233, 159−167. (41) Abel, S.; Mazzotti, M.; Morbidelli, M. Solvent gradient operation of simulated moving beds: I. Linear isotherms. J. Chromatogr. A 2002, 944 (1), 23−39.

(42) Wang, F. Y.; Zhu, Z. H.; Rudolph, V. Diffusion through ordered force fields in nanopores represented by Smoluchowski equation. AIChE J. 2009, 55 (6), 1325−1337.

12419

dx.doi.org/10.1021/ie502105q | Ind. Eng. Chem. Res. 2014, 53, 12411−12419