desorption processes

Separation and Purification Technology 235 (2020) 116145

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Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur

Bio-butanol recovery by adsorption/desorption processes a,⁎

b

a

T b

Francesca Raganati , Alessandra Procentese , Giuseppe Olivieri , Maria Elena Russo , Piero Salatinoa, Antonio Marzocchellaa a b

Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale – Università degli Studi di Napoli Federico II, P.le V. Tecchio 80, 80125 Napoli, Italy Istituto di Ricerche sulla Combustione – Consiglio Nazionale delle Ricerche, P.le V. Tecchio 80, 80125 Napoli, Italy

A R T I C LE I N FO

A B S T R A C T

Keywords: Adsorption Desorption Fixed-bed column Butanol Amberlite XAD-7

The Acetone-Butanol-Ethanol (ABE) fermentation route to produce chemicals and fuels from renewable resources still suffers from several issues that severely limit the industrial development. In particular, the low butanol concentration in the fermentation broth - due to butanol toxicity to microorganisms – affects the energy sustainability of technologies for butanol recovering. Novel techniques have been investigated in the last years. Among these, adsorption-based technique has been proposed as the most promising one. Present study reports on the assessment of the efficiency of butanol recovery according to adsorption and desorption processes. Tests were carried out using Amberlite XAD-7 as adsorbent material with respect to butanol, ethanol, acetone, and acetic/butyric acids in aqueous solutions. Amberlite XAD-7 was successfully used in fixed-bed column lab apparatus. Two desorption techniques were investigated – thermal drying/desorption and displacement desorption by methanol – to select the best candidate in terms of mass and energy efficiency. This study proved that Amberlite XAD-7 is a potential good adsorbent material to be successfully used in the process of butanol recovery. Amberlite XAD-7 was characterized by high adsorption capacity and selectivity towards butanol. Indeed, the adsorption capacity for acetone, butanol, ethanol, acetic and butyric acid was 17.1, 102.1, 4.2, 14.1 and 21.3 mg/g, respectively when using a solution of 13 g/L of butanol, 5.8 g/L of acetone, 1.6 g/L of ethanol, 6 g/L of acetic acid and 9 g/L of butyric acid. Moreover, adsorbed butanol was recovered as a high butanol concentration solution according to thermal (butanol concentration higher than 800 g/L) and chemical desorption processes (butanol concentration in methanol solution higher than 20 g/L, that is about 1.7 times the concentration in the stream used to saturate the resin). The stability of the performance of Amberlite XAD-7 bed with respect to butanol capture and concentration was provided by carrying out the adsorption–desorption cycle ten times. Butanol recovery was always higher than 97% for both the recovery techniques investigated. The overview of the energy demand for the proposed adsorption/thermal drying/desorption process was reported. The energy demand to concentrate butanol from diluted aqueous mixtures (about 13 g/L) is about 13 MJ/kgB, which is a fraction of the energy content of butanol (36 MJ/kgB).

1. Introduction Biobutanol has been proposed as a potential gasoline substitute due to its high energy density, low vapour pressure, low flammability and corrosiveness, weak hygroscopicity, and the possibility to be mixed with gasoline and diesel oil at any proportions [5,7]. The biotechnological route to produce butanol - the typical acetone–butanol–ethanol (ABE) fermentation – is very promising but some issues limit its industrial success. The issues include the cost of the feedstock, the low butanol specific productivity by microorganisms, and the low final butanol concentration due to butanol toxicity to microorganisms [28].

⁎

Butanol specific productivity is about 0.2–0.3 gB/gDM h for butanol concentration of about 5 g/L and drop drastically to zero as the maximum final total ABE concentration – about 20 g/L – is approached. Therefore, to provide high butanol productivities it has been suggested to increase the cell density and to keep butanol concentration below the toxic level, that is between 5 and 10 g/L [13,27]. However, the low value of butanol concentration makes the process for butanol recovering from the fermentation broth by the conventional distillation operation quite energy expensive and a huge amount of wastewater should be disposed [33]. Indeed, the energy required for the distillation of 0.5% (w/v) butanol-water solution is 79.5 MJ/kgB [22], larger than

Corresponding author. E-mail address: [email protected] (F. Raganati).

https://doi.org/10.1016/j.seppur.2019.116145 Received 12 June 2019; Received in revised form 6 September 2019; Accepted 29 September 2019 Available online 30 September 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved.

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selectivity to recover butanol (125 mg/g) while GAC was the best performing adsorbent at all initial acetic acid, ethanol and butanol concentration levels and all adsorbent doses investigated. Milestone and Bibby [23] carried out several tests to recover butanol from model solutions by adsorption on silicalite and they proposed a two-step recovery procedure. The first step of the recovery process provided water desorption from butanol-saturated silicalite by heating the bed to 40 °C. The second step was the heating up of the bed up to 150 °C to recover butanol. The maximum butanol adsorption capacity of butanol onto silicalite was quite low: lower than 100 mg/g at adsorption temperature of 20 °C and for butanol concentration in the fermentation broth of 21.5 g/L. Das et al. [6] investigated the adsorption of butanol from model solutions on various charcoals and resins (IRC-50, XAD-2, XAD-4, XAD8, and XAD-16). Desorption of butanol in a packed column was also studied by the Authors, by flowing hot air (120 °C) through the column bed. Butanol recovery was lower than 75–85%. Raganati et al. [31] reported a systematic investigation of the adsorption of metabolites typically present in the ABE fermentation broth: acetone, butanol, ethanol, acetic acid, butyric acid. The effect of glucose - as a carbon source for the ABE fermentation – and of the yeast extract on the adsorption efficiency of butanol was also investigated. Three adsorbents were characterized under batch adsorption modality: Amberlite XAD-4, Amberlite XAD-7 and Zeolite Y. The tests pointed out that Amberlite XAD-7 was characterized by the highest affinity for butanol (about 370 mg/g at temperature of 37 °C when butanol concentration in the solution was 12.5 g/L). The co-presence of all the metabolites in the solution was proved to affect the distribution in the adsorbed phase remarkably. The presence of glucose did not affect butanol adsorption. The present study moves a step further as regards the development of an adsorption-based process by using Amberlite XAD-7 in a fixed-bed column. The tests were carried out by using aqueous solutions of butanol and of butanol, acetone, ethanol, and acetic/butyric acids. The latter model solution closely emulated the composition of a real fermentation broth. Two desorption techniques were investigated – thermal drying/desorption and displacement desorption by methanol – to select which is the most appropriate for butanol recovery. The adsorption/desorption switch of the adsorbed bed column was repeated ten times to assess the performance and the stability of the process.

the energy content of the recovered butanol 34 MJ/ kgB [16]. Therefore, the conventional distillation process is definitely considered energy inefficient and makes the overall biobutanol production process un-competitive with respect to petrochemical-derived butanol production. Two strategies have been proposed in the last decades to manage the drawbacks related to the low butanol concentration in the fermentation broth. The first strategy regards the strain tolerance to butanol. The second strategy regards the recovery/concentration process of butanol from the fermentation broth. Various mutagenic techniques were implemented in organism level to increase butanol tolerance of Clostridia strains: several butanol tolerant strains were developed from classical butanol producer organism (Clostridium acetobutylicum) using mutagenesis and genetic manipulation [18,8,19]. The second strategy is the selection of a recovery/concentration process of butanol that would be un-expensive and high energy efficiency. The latter strategy may also have a twofold advantage when it is possible to couple the separation technique with the fermentation step in order to keep butanol concentration below the threshold of toxicity. As an alternative to distillation, several in situ product removal techniques such as liquid–liquid extraction [17], ionic liquids [4], perstraction [10], gas stripping [9], aqueous two-phase separation [9], pervaporation [38], and adsorption [24,34,1]have been investigated. Each technique is characterized by a spectrum of advantages and disadvantages in terms of capacity, selectivity, fouling, clogging, scale-up, operating simplicity, and energy demand [21]. Although these in situ product recovery techniques have been applied in laboratory-scale bioreactors, only the chromatographic separation technology (e.g. adsorption) has been proved to be a superior recovery technique. Indeed, it has been suggested that it could be applied successfully for energy-efficient removal of butanol from fermentation broth in industrial application [24]. The application of the commercial adsorbents typically used in wastewater processes (i.e., silicalite, bonopore, polyvinylpyridine, zeolite, activated car bon, and polymeric resins) has been restricted due to their low butanol adsorption capacity, low butanol adsorption selectivity, low butanol desorption efficiency, and low concentration of butanol in butanol produced stream. Xue et al. [37] reviewed integrated butanol recovery techniques, and reported activated carbon, zeolite, and polymeric resins as the most common adsorbents for the recovery of butanol from acetone-butanolethanol (ABE) aqueous solutions. A suitable adsorbent for the recovery of fermentation products should have a high adsorption capacity, high selectivity, stability (mechanical, thermal and chemical), and no toxicity to the fermenting microorganisms in case of in-situ recovery [35]. Huang et al. [15] reviewed the application of a spectrum of adsorbents (e.g. Dowex Optipore™ L-493 and Diaion® HP-20) for the recovery of butanol from fermentation broths. The Authors reported that polystyrene-co-divinylbenzene resins had the highest affinity for butanol compared to the other resins investigated, and the specific surface area was the performance determining factor for the resin’s adsorption capacity. Sadrimajd et al. [32] studied the adsorptive capability of granular activated carbon (Norit® 1240w GAC) and the resins Dowex Optipore™ L-493 and Diaion® HP-20 to selectively recover acetic acid, ethanol, and butanol (AEB) from multi-component systems. Tests were carried out at pH higher than the pKa of acetic acid and at concentrations of acetic acid, ethanol, and butanol close to an optimized fermentation broth. The Authors proved that the L-493 resin was characterized by good

2. Materials and methods 2.1. Materials The chemicals were of high-purity analytical grade from SigmaAldrich. 1-Butanol (purity 99.5%), acetone (purity 99.9%) and ethanol (purity 99.9%), acetic acid (purity 99.9%), butyric acid (purity 99.9%) and glucose were used. Amberlite XAD-7 was used as adsorbent material; this material is often used to adsorb molecules up to MW 60,000 (e.g. insulin recovery, metal ions, dry waste, organic compounds removal and recovery, antibiotic recovery). Amberlite was washed with water. Table 1 reports some relevant features of the adsorbent investigated.

Table 1 Adsorbent features (Sigma-Aldrich Product Information Sheet). Materials

Chemical nature

Dry density (g/mL)

Specific superficial area (m2/g)

Pore diameter (Angstrom)

Specific pore volume (mL/g)

Amberlite XAD-7

Acrylic ester (dipol moment 1.8).

1.24

450

90

1.14

2

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2.2. Adsorption tests

continuous adsorption tests (BA and TM-A solutions).

Tests were carried out in duplicate. The reported results are the mean values of the measured/assessed values. The error was always within the 5%.

2.4.1.1. Batch tests. The saturated adsorbent (which was previously exposed to a solution of 13 g/L of butanol at T = 20 °C) was filtered using Whatman filter paper and rinsed with distilled water to remove adhered species. The spent adsorbent (0.5 g) was mixed with 6.25 mL methanol solution and agitated for 24 h at 120 rpm at room temperature. The methanol concentration of the solution was set at: 30, 60, 70, 80, 85, 90, and 95% v/v. The concentration of the solvent/ acids in the liquid phase was analysed by GC. The concentration of chemicals at the equilibrium were processed to assess the desorption fraction according to Eq. (1):

2.2.1. Batch tests Batch adsorption equilibrium tests were carried out in 50 mL closed vials filled with 25 mL liquid solution. The vials contained a pre-set amount of butanol, water and adsorbent. Typically, 0.5 g of adsorbent were used. The vials were housed in a thermostatic shaker for 24/48 h under orbital agitation set at 120 rpm. Batch adsorption tests were carried at T = 20 °C. Details of the tests are reported in Raganati et al. [31].

D=

ci, X ·VX mi, ads

(1)

where mi,ads is the mass of species “i” adsorbed, Ci,X and Vx are the concentration of the adsorbate in the methanol solution and the methanol solution volume, respectively. The mi,ads was assessed by processing the experimental data according to Eq. (2):

2.2.2. Continuous adsorption tests A glass column of 125 mL (20 mm ID, 400 mm long) was used for continuous tests. The adsorbent was used under fixed-bed conditions. Butanol bearing solution was fed at the bottom of the column by a peristaltic pump. The column was loaded with 67 g of wet adsorbent to form a bed characterized by height 29 cm and free volume 64 mL. The stream from the column was sampled to assess the competitive breakthrough curve of each adsorbate. The exhaust stream was characterized in terms of the concentration of ABE and acids.

mi, ads = (ci,0 − ci, e )·VF

(2)

where Ci,0 is the initial concentration of adsorbate “i“ in the solution, Ci,e the concentration of the adsorbate in the solution under equilibrium conditions, VF the volume of solution mixed with the adsorbent.

2.3. Operating conditions 2.4.1.2. Fixed-bed tests. The pre-saturated resin (with solutions BA and TM-A at 20 °C) was washed continuously with methanol to desorb acetone, butanol, ethanol, acetic and butyric acid. The desorption test was carried out with a resin bed just saturated by feeding a solution (BA and TM-A) characterized by pH set at 5 (see Section 2.2.1). The effluent was sampled at predetermined time intervals to characterize the desorption behaviour of fermentation broth on Amberlite XAD-7 resin. The resin bed was washed with three bed volumes of deionized water to restore the adsorption capacity before to use in a successive adsorption test. Adsorption/desorption/regeneration cycle was repeated at least 10 times to assess the extension of Amberlite XAD-7 regeneration and the adsorption capacity stability of the resin with the cycles.

Fixed bed adsorption tests were carried out by feeding solutions of solvents and acids at pre-set composition. The liquid volumetric flow rate was set at about 140 mL/h (about 2.2 bed volumes per hour): the liquid residence time was about 25 min. Adsorption temperature was set at 20 °C and 37 °C. Adsorption tests were grouped as reported hereinafter:

• BA: Butanol adsorption tests. The solution composition: 13 g/L of butanol; • TM-A: ABE Ternary Mixture supplemented with acids (acetic and

•

butyric acid). The solution composition was: 13 g/L of butanol, 5.8 g/L of acetone, 1.6 g/L of ethanol, 6 g/L of acetic acid and 9 g/L of butyric acid. The solution mimed the effluent of the reactor system reported by Raganati et al. [30]. Tests were carried out without pH control and with pH set at 5; TM-A2: ABE Ternary Mixture supplemented with acetic and butyric acid. The total acid initial concentration was a function of the total solvent initial concentration. The solution composition was set to provide: ABE molar ratio 3:6:1, acetic acid to butyric acid ratio = 0.7 g/g, acids to solvents ratio = 0.6 g/g [30]. Total ABE initial concentration was set at 5, 10, 20, 30, 60 and 100 g/L. Total acid initial concentration was set at 3, 6, 12, 18, 36 and 60 g/L. The pH of the feeding solution was set at 5.

2.4.2. Thermal desorption Tests were carried out with pre-saturated resin bed (with solutions BA and TM-A at 37 °C and pH set at 5). The column was carefully drained to remove the interstitial liquid. 2.4.2.1. Drying step. The drained column was purged with nitrogen at low temperature (60 °C). The effluent is sent to a cold trap operating at 0 °C. During this step the unbound liquid (liquid not adsorbed filling pipes and interstices with the same concentration as the feed mixture) is removed. 2.4.2.2. Desorption step. The column is heated at high temperature (140 °C) and purged with nitrogen; the effluent is sent to a cold trap operating at 0 °C for recovering butanol/ABE-acids adsorbed in Amberlite XAD-7 crystals by condensation. Adsorption/desorption cycle was repeated at least 10 times to assess the extension of Amberlite XAD-7 regeneration and the adsorption capacity stability of the resin with the cycles

Batch adsorption tests were carried out with BA solution at 20 and 37 °C. 2.4. Desorption tests Tests were carried out in duplicate. The reported results are the mean values of the measured/assessed values. The error was always within the 5%.

2.5. Analytical methods 2.4.1. Chemical desorption Two typologies of chemical desorption tests were carried out. The first typology of desorption tests was carried out with adsorbents presaturated according to the batch adsorption with a butanol solution at 13 g/L initial concentration. The second typology of desorption tests was carried out with an adsorbent bed pre-saturated according to the

Sugar concentration. Sugar concentration was measured by means of high performance liquid chromatography (HPLC) using an Agilent 1100 system (Palo Alto, CA). Sugars were separated on a 8 µm Hi-Plex H, 30 cm 7.7 mm column at room temperature and detected by means of a refractive index detector. Deionized water was used as mobile phase at 3

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a flow rate of 0.6 mL/min. 20 µL of sample were injected in the column. Typically, sugar resolution was carried out in 10–13 min [29]. Acid and alcohol concentration. A GC apparatus equipped with a FID, and outfitted with a capillary column Poraplot Q (25 m × 0.32 mm) was used for the analysis of acids (acetic acid, butyric acid) and alcohol (ethanol, butanol) concentration. An internal standard (hexanoic acid) was used to assess acids and alcohols and their concentrations [30].

ΔHTOT (MJ / kgB ) =

2.6.1. Adsorption The adsorption performance of the fixed-bed column has been characterized by processing the time series of the normalized concentration of the effluent (Cout/C0) vs. time curves (breakthrough plot). The total amount of the generic species i (acetone, butanol, ethanol, acetic acid and butyric acid) adsorbed per mass of dry resin up to the saturation (under equilibrium conditions) may be calculated from the breakthrough curve according to the Eq. (3).

ci,0 Q mads

∫ ⎛1 − ⎜

⎝

ci, out ⎞ ⎟ dt ci,0 ⎠

ci,0 Q mads

j=t f

∑ j=0

3.1. Adsorption tests Fig. 2 reports the breakthrough curve for adsorption of butanol measured during a BA test at 20 °C. The adsorption capacity of the adsorber was calculated according to Eq. (4). The amount of butanol adsorbed was also assessed. The mass of adsorbed butanol was 3.34 g that is an adsorption capacity of about 99.7 mg/g, in agreement with data reported by Raganati et al. [31]. Fig. 3 reports the competitive breakthrough curves for adsorption of ABE and acids measured during a TM-A test carried out at 20 °C. For the sake of comparison, the dimensionless concentration - defined as the ratio of the outlet concentration to the feeding concentration (Cout/C0) was reported. Fig. 3 A reports the competitive breakthrough curves measured during an adsorption test TM-A (pH not adjusted). The elution time for the investigated species increased according to the order: E, A, AA, BA, B. Ethanol is the weakest retained component and butanol the strongest retained component, whereas acetone, acetic and butyric acid being in between ethanol and butanol. It is worth to note that a significant bump can be observed in the concentration vs. time data of ethanol, acetone and acetic acid in Fig. 3A. The concentration of E, A and AA approaches the equilibrium value according to an “underdamped” behaviour: the concentration in the effluent of weak retained components during a finite time interval was larger than that in the feeding. This “underdamped” behaviour is due to the displacement of the weak adsorbed species by the strong adsorbed species, a behaviour typical of the competitive adsorption [36]. The mass of adsorbate – acetone, butanol, ethanol, acetic, and butyric acid - per unit mass of adsorbent (qe) is reported in Table 2. Fig. 3 B reports the competitive breakthrough curves for adsorption carried out according to a TM-A test (pH set at 5, temperature at 20 °C). The elution time for the investigated species increased according to the order: BA, AA, E, A, B. The underdamped behaviour of some species was still present. The mass of adsorbate – acetone, butanol, ethanol, acetic and butyric acid - per unit mass of adsorbent (qe) measured during the test in Fig. 3B is reported in Table 2. The analysis of Table 2 points out that under the operating conditions set for the test reported in Fig. 3B the acid adsorption decreased and solvent adsorption increased. The change in the elution order and the decrease/increase in the adsorption capacity of acids/solvents with respect to data measured in the test reported in Fig. 3A points out the effect of the pH on the acid adsorption. The protonated form of acids was characterized by higher affinity for Amberlite XAD-7 than the deprotonated form of the acids [11;14;31]. The competitive adsorption of the main products present in the ABE fermentation broth was investigated. A campaign of tests included multicomponent adsorption runs by feeding Amberlite XAD-7 bed with solutions bearing ABE-acids at different concentration (Test TM-A2, 37 °C). In particular, the concentration ratio A:B:E:AA:BA were set at values typical of ABE fermentation broth - ABE molar ratio 3:6:1, acids/ solvents 0.6 g/g, AA/AB 0.7 g/g [31]- and the total solvent-acid concentration ranged between 8 and 160 g/L. The concentration in the solid phase (qi) and in the liquid phase (ci) under equilibrium

(3)

⎛1 − ci, j ⎟⎞ Δt j ci,0 ⎠ ⎝

⎜

(4)

Data of adsorption tests at constant temperature were processed to assess the equilibrium features For a generic i-component present in a n-multi-component solution the Langmuir model is described by Eq. (5) [25,12]:

qi, e =

qmax ·KL, i·ci, e n

1 + ∑ j = 1 KL, i·cj, e

(5)

where ci,e is the concentration of the adsorbate in the solution at the equilibrium, qmax the monolayer capacity (the amount of adsorbate per unit mass of adsorbent required to occupy all adsorption sites on the solid surface), and KL,j an adsorption constant for the i-component. The Langmuir model parameters were estimated using nonlinear least squares regression via the lsqcurvefit function in MATLAB. 2.6.2. Energy requirement calculations The drying and desorption results have been processed to estimate the energy requirements for both butanol-water and ABE/acids-water mixture tests. The conceptual process flow sheets reported in Fig. 1 were considered: they report the energy inputs (heating and refrigeration). The energy requirement of the adsorption step was not included in the analysis because both the adsorption heat and the liquid pumping power were neglected [2]. The energy balance applied to the drying and desorption steps is proposed. Equations (6) and (7) included the enthalpy required for heating and cooling the investigated system:

ΔHdrying (MJ ) = mAmb ·cpAmb (60 − 25) + m N2 ·cp N2 (60 − 25) + mi °

drying ·cpi (60 − 25) + mRi ·Λ i60 C

(6)

ΔHdesorption (MJ ) = m N2 ·cp N2 (140 − 25) + mAmb ·cpAmb (140 − 60) drying + (mi − mRi )·cpi (140 − 60)+ °

desorption desorption C + mRi ·Λ140 − mRi ·cpi (0 − 140) − m N2 ·cpi (0 − 140) i °

desorption − mRi ·Λ i0 C − mAmb ·cpi (25 − 140)

(8)

3. Results and discussion

where ci,0 is the initial concentration of adsorbate i in the solution, ci,out the concentration of the adsorbate i in the effluent. In particular, the discretized version of Eq. (3) was used in the present investigation:

qi, e =

mRB

where Λi is the heat of evaporation/condensation of the species “i“ (water, ABE, acids), cp the specific heat capacity of the species “i” (water, ABE, acids), mAmb the mass of the adsorbent, mN2 the mass of nitrogen, mi the mass of the species “i“ (water, ABE, acids), mRidrying the mass of recovered species “i” during the drying step, mRidesorption the mass of recovered species “i” during the desorption step, mi the mass of the species “i” (water, ABE, acids).

2.6. Theoretical framework

qi, e =

ΔHdrying + ΔHdesorption

(7) 4

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Fig. 1. Flow-sheets for the drying and desorption steps in an adsorption/drying/desorption process for recovering butanol from a diluted aqueous mixture.

Fig. 2. Breakthrough curve for adsorption of butanol in the fixed bed. Resin bed mass = 67 g; C0 = 13 g/L; T = 20 °C; Q = 140 mL/min.

conditions for each specie in the ABE/acids mixture are reported in Fig. 4. The regression of data in Fig. 4 was carried according to the competitive multicomponent Langmuir isotherm (Eq. (5)). The calculated competitive isotherm model parameters for ABE-acids are reported in Table 3 and the Eq. (5) is plotted in Fig. 4. It can be observed that the prediction curves are in good agreement with the experimental data. 3.2. Chemical desorption tests Fig. 5 reports the desorption tests of Amberlite XAD-7 pre-saturated with a BA solution (B = 13 g/L) at T = 20 °C. Butanol was desorbed by means of a 85% (v/v) methanol stream fed at 140 mL/min (dead time 25 min). The maximum concentration of butanol was measured at 5 min and it was about 160 g/L: higher than the concentration in the saturation stream (13 g/L). 100% of butanol was recovered in about 40 min. The time averaged concentration of butanol in the stream collected over 40 min was about 23 g/L. The comparison with the saturation process (butanol concentration 13 g/L) points out that butanol concentration in the methanol was increased by a factor of about 1.8. A campaign of batch tests was carried out to investigate the effect of

Fig. 3. Competitive breakthrough curves for adsorption of ABE-acids (test TMA) in the fixed bed. Resin bed mass = 67 g; C0 = 13 g/L of butanol, 5.8 g/L of acetone, 1.6 g/L of ethanol, 6 g/L of acetic acid and 9 g/L of butyric acid. T = 20 °C; Q = 140 mL/min. A) without pH control of the feeding solution; B) pH of the feeding solution set at 5.

the solvent polarity on the desorption of butanol from the resin. The pre-saturated resin – saturated with a butanol solution of 13 g/L at T = 20 °C - was filtered using Whatman filter paper and rinsed with 5

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Table 2 Amberlite XAD-7 adsorption capacity for acetone, butanol, ethanol, acetic and butyric acid at 20 °C for Test TM-A without pH control and with pH set at 5. COMPONENT

Acetone Butanol Ethanol Acetic Acid Butyric Acid

Table 3 Competitive Langmuir parameters for Amberlite XAD-7 at 37 °C. Solvent

qe – mg/gads without pH control

pH set at 5

15.1 86.1 3.9 16.2 66.6

17.1 102.1 4.2 14.1 21.3

Acetone Butanol Ethanol Acetic Acid Butyric Acid

distilled water to remove adhered species. The spent adsorbent (0.5 g) was mixed with 6.25 mL methanol solution (methanol concentration set between 30% (v/v) and 95% (v/v)) and agitated for 24 h at 120 rpm at room temperature. Results of desorption tests are reported in Fig. 6. The desorption efficiency was characterized by a maximum at about 15% of water. As expected, the recovery of butanol from the resin increased with increasing polarity of the solvent: the recovery increased from 96 to 100% as the water fraction increased from 5 to 15%. The progressively decrease of desorption efficiency with the increase of the water fraction may be due to the low solubility of butanol in water (73 g/L at T = 25 °C) when compared with the complete miscibility in methanol. The direct observation of the resin particles pointed out that Amberlite XAD-7 swelled a bit in methanol solutions. Fig. 7 reports the desorption tests of Amberlite XAD-7 pre-saturated with a TM-A solution at T = 20 °C and pH set at 5. Butanol was desorbed by means of a 85% (v/v) methanol stream fed at 140 mL/min (dead time 25 min). The maximum concentration of acetone, butanol, ethanol, acetic and butyric acid in the eluent were measured at 5 min and they were about 18.4, 174, 8.8, 17.9, and 22.9 g/L, respectively. The maximum concentrations were definitely higher the concentration set in the solution used to saturate the resin (13 g/L of butanol, 5.8 g/L of acetone, 1.6 g/L of ethanol, 6 g/L of acetic acid and 9 g/L of butyric acid). The total recovery of these five components was: 99.6% of acetone, 99.5% of butanol, 100% of ethanol, 100% of acetic acid and 99.7% of butyric acid were recovered in about

Langmuir parameters qmax – mg/gads

KL- L/g

878

0.0041 0.02088 0.0035 0.0047 0.0046

Fig. 5. Desorption of butanol from a pre-saturated bed by using 85% (v/v) methanol solution. Pre-saturation: BA solution at T = 20 °C. Methanol solution flow rate: 140 mL/h Temperature: 20 °C.

80 min. The time averaged concentration of butanol in the eluent – calculated between the beginning of the desorption step and the instant at which butanol concentration at the exit of the column was zero - was about 22.2 g/L, 1.7 times the concentration in the stream used to saturate the resin (13 g/L). The increase of butanol concentration in the

Fig. 4. Competitive isotherms for Amberlite XAD-7, T = 37 °C. 6

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mol (under standard conditions: 298.15 K and 1 atm). Moreover, no azeotrope is present for butanol-methanol system. Therefore, the energy required to produce pure butanol is expected to be lower than that required for the system butanol-water. The bed of Amberlite XAD-7 was washed with water (three bed volumes) after butanol recovery. The large amount of water and the complete miscibility of methanol in water provided the complete regeneration of the bed. 3.2.1. Chemical desorption tests: Long time stability The stability of Amberlite XAD-7 bed with respect to butanol capture and concentration was provided by carrying out the adsorption–desorption–regeneration cycle for ten times. The bed saturation was carried out by feeding the bed with a butanol solution or a mixture of ABE and acids. Butanol recovery was carried out by feeding a 85% (v/v) methanol solution. The bed regeneration was carried out by feeding water. The mass of butanol adsorbed (and desorbed) for adsorbent mass unit were measured as a function of the cycle number at T = 20 °C. The mass of the adsorbed butanol (i.e. the resin capacity) was almost constant with the cycle number (about 98.2 ± 1.31 mgB/g) and it was completely removed during the desorption step. The results confirmed that Amberlite XAD-7 is a potential good adsorbent to be successfully used in the process of butanol recovery.

Fig. 6. Effect of different methanol concentration on butanol desorption from Amberlite XAD-7.

3.3. Thermal drying/desorption tests The thermal drying/desorption tests were carried out with Amberlite XAD-7 pre-saturated with: (i) BA solution, T = 37 °C; (ii) TMA solution, T = 37 °C and pH set at 5. Once saturated, the column was carefully drained to remove the interstitial liquid. Then, the saturated packed column was placed in the drying/desorption setup. Drying was carried out setting the column wall temperature to 60 °C, and purging the bed with a nitrogen stream (volumetric flow rate 40 mL/min). The gas stream from the column was sent to a cold-trap operating at 0 °C where condensable components were separated as liquid phase. The drying step extended up to the instant at which no more liquid accumulated in the cold trap, typically 3 h. The desorption process continued by flushing with nitrogen stream (volumetric flow rate 40 mL/min) and setting the bed temperature at 140 °C. The gas from the column was still sent to the cold-trap operating at 0 °C. The composition of the liquid collected in the trap during the drying step was: 13.8 g/L butanol when the column was saturated by feeding the BA; 13.7 g/L butanol, 46 g/L acetone, 3.22 g/L ethanol, 5.2 g/L acetic acid and 7.3 g/L butyric acid when the column was saturated by feeding the TM-A solution. The increase of the concentration in the liquid phase in the cold trap with respect to the initial unbound liquid concentration is due to the desorption of a portion of bound compounds

Fig. 7. Desorption of ABE-acids from a pre-saturated bed by using 85% (v/v) methanol solution. Pre-saturation: TM-A solution at T = 20 °C and pH set at 5. Methanol solution flow rate: 140 mL/h Temperature: 20 °C.

product stream has a remarkable economic impact [20]. Investigations on butanol recovery from the fermentation broth by means of distillation technology pointed out that the energy required for butanol distillation was approximately halved as the concentration of butanol increased from 12 to 19 g/L [26]. In the present case the condition is still more promising because butanol concentration was larger than 22 g/L and the solvent was methanol. Indeed, the boiling point of methanol and the vaporization heat are lower than water: 64 °C and 38 kJ/mol (under standard conditions: 298.15 K and 1 atm) vs. 100 °C and 44 kJ/

Table 4 Results of ten adsorption–desorption cycles for butanol separation from butanol–water binary solutions. Cycle

Initial B (g/L)

Adsorption capacity (mg/g)

B desorbed (g)*

B in desorbed up-phase (g)*

B in desorbed up-phase (g/L)*

B in desorbed low-phase (g)*

B in desorbed low-phase (g/L)*

B Recovery (%)*

1 2 3 4 5 6 7 8 9 10

13

367.7 366.7 368.1 368.2 368 366 365 360 356 362

12.3 12.2 12.3 12.3 12.3 12.3 12.3 12.1 11.9 12.2

11.64 11.63 11.75 11.74 11.74 11.76 11.70 11.48 11.32 11.63

790 770 794 793 799 800 770 750 755 755

0.61 0.62 0.57 0.57 0.56 0.53 0.59 0.57 0.55 0.55

80 78 77 77 77 75 78 78 77 77

99.5 99.7 99.9 99.8 99.8 99.9 99.9 99.9 99.6 99.9

* values refer only to the desorption step (drying step was not considered). 7

Separation and Purification Technology 235 (2020) 116145

0-80-0-138-120.5 0-80-0-140-129 0-80-0-125-118 0-80-0-137-126 0-80-0-137-125 0-80-0-136-124 0-80-0-138-125 0-80-0-129-124.5 0-80-0-128-122.5 0-80-0-138-126.5

0-98.1-0-99.7-99.9 0-97.7-0-99.9-99.7 0-99.7-0-98.5-99.6 0-99.2-0-99.6-99.4 0-98.6-0-99.5-99.2 0-99-0-99.9-99.5 0-99.9-0-99.7-99.8 0-99.4-0-99.8-99.9 0-99.8-0-99.5-99.7 0-98.4-0-99.8-99.9

Table 6 Energy demand to recover ABE from fermentation broth according to different processes. Solution

ΔHdrying MJ

ΔHdesorption MJ

ΔHTOT MJ/kgB

Butanol - water ABE & acids - water

3.8 * 10−2 3.9 * 10−2

7.2 * 10−2 3.2 * 10−2

9 13.1

0-805-0-0.5-0.7 0-805-0-0.6-0.7 0-804-0-0.5–0.7 0-805-0-0.4-0.6 0-805-0-0.5-0.7 0-805-0-0.5-0.7 0-805-0-0.5-0.7 0-805-0-0.5-0.7 0-810-0-0-5-0.7 0-805-0-0.5-0.7

0-0.32-0-0.55-0.48 0-0.31-0-0.55-0.5 0-0.32.0-0.5-0.5 0-0.32-0-0.55.0.5 0-0.32-0-0.55-0.5 0-0.32-0-0.54-0.5 0-0.32-0-0.55-0.5 0-0.32-0-0.52-0.5 0-0.32-0-0.51-0.49 0-0.32-0-0.55-0.51

during the drying step. In particular, 99.6% of acetone and 99.7% of ethanol were recovered during the drying step. The liquid condensed in the trap during the desorption step was characterized and data are presented hereinafter. The desorption process recovery - defined for each adsorbed species as the ratio between the recovered mass and the adsorbed mass during the adsorption step is reported in Tables 4 and 5. At the end of the desorption step a twophase liquid system was recovered: a floating butanol rich phase and bottom phase water rich (concentration reported in Tables 4 and 5). The stability of Amberlite XAD-7 bed with respect to butanol capture and concentration was provided by carrying out the adsorption/ drying/desorption cycle ten times. The bed saturation was carried out by feeding the bed with a butanol solution (BA solution) or a mixture of ABE and acids (TM-A solution, pH set to 5) as feed solutions. The mass of ABE/acids adsorbed (and desorbed) for adsorbent mass unit were almost constant with the cycle number: 18.6 ± 0.96 mg of acetone for g of adsorbent, 100.3 ± 2.37 mg of butanol for g of adsorbent, 4 ± 0.14 mg of ethanol for g of adsorbent, 14 ± 0.14 mg of acetic acid for g of adsorbent, 21.9 ± 0.87 mg of butyric acid for g of adsorbent. Tables 4 and 5 report the results of the ten adsorption/thermal desorption cycles carried out for butanol/ABE-acids model solutions. These results showed that Amberlite XAD-7 adsorption capacity for each species was almost constant for all cycles and the recovery obtained was always higher than 97%. It may be pointed out that: (i) all the adsorbed components were completely desorbed during the desorption step; (ii) the adsorbent particles preserved their adsorbent characteristics throughout the continuous adsorption process. The drying and desorption results were used for the estimation of the energy demand for both the drying and desorption processes, for both butanol-water and ABE/acids-water mixture tests. The energy demand of the drying and desorption steps – assessed using Eq.s 6, 7 and 8 - is reported in Table 6. These results support that the energy demand to concentrate butanol from diluted aqueous mixtures (e.g. fermentation broth) is theoretically a fraction of the energy content of butanol (36 MJ/kgB). Table 7 reports an overview of the energy demand for butanol recovery from the fermentation broth – or synthetic mixtures – according to a spectrum of separation processes reported in the literature. The analysis of the data reported in Table 7 suggests that the energy demand for the proposed adsorption/drying/desorption process is:

* Values refer only to the desorption step (drying step was not considered).

0-5.07-0-0.003-0.005 0-5.1-0-0.004-0.004 0-5.1-0-0.003-0.005 0-5.1-0-0.003-0.004 0-5.1-0-0.003-0.004 0-5.13-0-0-003-0.004 0-5.18-0-0.003-0.005 0-5.07-00.003-0.04 0-5.27-0-0.003-0.005 0-5.07-0-0.003-0.004 0-5.4-0-0.56-0.49 0-5.5-0-0.55-0.51 0-5.5-0-0.51-0-48 0-5.5-0-0.55-0-51 0-5.5-0-0.55-0.51 0-5.5-0-0.55-0.51 0-5.5-0-0.56-0.51 0-5.4-0-0.52-0.5 0-5.6-0-0.52-0.5 0-5.5-0-0.56-0.51 1 2 3 4 5 6 7 8 9 10

5.3-13-1.5-5-7

19.5-164-0.87-16.6-14.5 20.5-164.4-1.12-16.4-15.2 19.3-163.7-0.86-15.3-14.3 20.5-163.1-0.95-16.5-15.3 20.5-163.2-1-16.53-15.16 20.4-164.2-1.21-16.32-15 20.4-164.3-0.98-16.6-15.1 18.9-161.9-1.92-15.52-15 20.3-167-1.03-15.45-14-81 20.7-163.5-1.3-16.6-15.23

A-B-E-AA-BA in desorbed up-phase (g)* A-B-E-AA-BA desorbed (g)* A-B-E-AA-BA Adsorption capacity (mg/g) Initial A-B-E-AA-BA (g/L) Cycle

Table 5 Results of ten adsorption–desorption cycles for ABE-acids separation from ABE-acids solutions.

A-B-E-AA-BA in desorbed up-phase (g/L)*

A-B-E-AA-BA in desorbed low-phase (g)*

A-B-E-AA-BA in desorbed low-phase (g/L)*

A-B-E-AA-BA Recovery (%)*

F. Raganati, et al.

• lower than that assessed for gas stripping/distillation and for gasstripping/pervaporation/distillation hybrid process; • comparable to that assessed for liquid–liquid extraction (LLE) pro•

cess. It should be pointed out that this assessment is based on the simulated flowsheet proposed by Salemme et al. [33] including water, butanol, acetone, and ethanol and neglecting acetic and butyric acid; higher than that the ADD process proposed by Águeda et al. [2]. Two issues should be highlighted for this assessment: (i) calculations were carried out just for butanol-water solution; (ii) they assumed that a fraction of the heat input is recovered by cooling the effluent of the column before the condensation step.

Altogether, the reported results support that the thermal desorption process provides total butanol recovery and resin regeneration with a 8

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F. Raganati, et al.

Table 7 Energy requirement to separate ABE from fermentation broth using different recovery techniques. Recovery process

hybrid process gas-stripping/distillation (GSD) gas-stripping/pervaporation/distillation (GSPD) hybrid process Liquid-liquid extraction (LLE) adsorption/drying/desorption (ADD) adsorption/drying/desorption (ADD)

Butanol concentration jump

Specific Energy demand

From (g/L)

To (g/L)

MJ/kgB

7.8 10 18 20 13 13

Pure* > 800 807 797 > 800 > 800

21 23 9.9 3.4 9a 13.1b

Ref.

[15] [3] [33] [2] This work

* pure butanol, without detailed purity data. a Adsorption step carried out with butanol-water solution. b Adsorption step carried out with ABE&acids-water solution. [5] R. Cascone, Biobutanol – a replacement for bioethanol? Chem Eng Prog 104 (2008) S4–S9. [6] K. Das, B. Soni, T. Ghose, Static and Column Studies on Selective AdsorptionDesorption of Butanol, 1985, Elsevier, Amsterdam, The Netherlands, 1985, p. 611. [7] P. Dürre, Biobutanol: an attractive biofuel, Biotechnol. J. 2 (2007) 1525–1534. [8] T.C. Ezeji, N. Qureshi, H.P. Blaschek, Butanol fermentation research: upstream and downstream manipulations, Chem. Rec. 4 (2004) 305–314. [9] T.C. Ezeji, N. Qureshi, H.P. Blaschek, Acetone butanol ethanol (ABE) production from concentrated substrate: reduction in sub- strate inhibition by fed-batch technique and product inhibition by gas stripping, Appl. Microbiol. Biotechnol. 63 (2004) 653–658. [10] T.C. Ezeji, N. Qureshi, H.P. Blaschek, Bioproduction of butanol from biomass: from genes to bioreactors, Curr. Opin. Biotechnol. 18 (2007) 220–227. [11] A. Faisal, A. Zarebska, P. Saremi, D. Korelskiy, L. Ohlin, U. Rova, J. Hedlund, M. Grahn, MFI zeolite as adsorbent for selective recovery of hydrocarbons from ABE fermentation broths, Adsorption 20 (2013) 465–470. [12] M.C. Flickinger, S.W. Drew, Downstream Industrial Biotechnology: Recovery and Purification, Wiley, New York, 1999. [13] A. Friedl, Downstream process options for the ABE fermentation, FEMS Microbiol. Lett. 363 (2016) 1–5. [14] R. Goerlitz, L. Weisleder, S. Wuttig, S. Trippel, K. Karstens, P. Goetz, H. Niebelschuetz, Bio-butanol downstream processing: regeneration of adsorbents and selective exclusion of fermentation by-products, Adsorption 24 (1) (2018) 95–104. [15] H.J. Huang, S. Ramaswamy, Y. Liu, Separation and purification of biobutanol during bioconversion ofbiomass, Sep. Purif. Technol. 132 (2014) 513–540. [16] T. Ikegami, H. Negishi, K. Sakaki, Selective separation of n-butanol from aqueous solutions by pervaporation using silicone rub- ber-coated silicalite membranes, J. Chem. Technol. Biotechnol. 86 (2011) 845–851. [17] K. Kraemer, A. Harwardt, R. Bronneberg, W. Marquardt, Separa- tion of butanol from acetone–butanol–ethanol fermentation by a hybrid extraction-distillation process, Comput. Chem. Eng. 35 (2011) 949–963. [18] M. Kumar, K. Gayen, Developments in biobutanol production: new insights, Appl. Energy 88 (2011) 1999–2012. [19] S.Y. Lee, J.H. Park, S.H. Jang, L.K. Nielsen, J. Kim, K.S. Jung, Fermentative butanol production by Clostridia, Biotechnol. Bioeng. 101 (2008) 209–228, https://doi.org/ 10.1002/bit.22003. [20] X. Lin, J. Wu, X. Jin, J. Fan, R. Li, Q. Wen, W. Qian, D. Liu, X. Chen, Y. Chen, J. Xie, J. Bai, H. Ying, Selective separation of biobutanol from acetone-butanol-ethanol fermentation broth by means of sorption methodology based on a novel macroporous resin, Biotechnol. Prog. 28 (2012) 962–972. [21] A.P. Mariano, M.J. Keshtkar, D.I.P. Atala, F. Maugeri Filho, M.R. Wolf Maciel, R. Maciel Filho, P. Stuart, Energy requirements for butanol recovery using the flash fermentation technology, Energ Fuel. 25 (2011) 2347–2355. [22] M. Matsumura, H. Kataoka, M. Sueki, K. Araki, Energy saving effect of pervaporation using oleyl alcohol liquid membrane in butanol purification, Bioproc. Biosyst. Eng. 3 (1988) 93–100. [23] N.B. Milestone, D.M. Bibby, Concentration of alcohols by adsorp- tion on silicalite, J. Chem. Technol. Biotechnol. 31 (1981) 732–736. [24] D.R. Nielsen, K.J. Prather, In situ product recovery of n-butanol using polymeric resins, Biotechnol. Bioeng. 102 (2009) 811–821. [25] R.H. Perry, D.W. Green, J.O. Maloney, Perry's Chemical engineers' handbook, McGraw-Hill, New York, 1984. [26] J.A. Phillips, A.E. Humphrey, An overview of process technology for the production of liquid fuels and chemical feedstocks via fermentation, in: D.L. Wise (Ed.), Organic Chemicals from Biomass, Benjamins/Cummings Publishing, Menlo Park, California, USA., 1983, pp. 249–304. [27] A. Procentese, F. Raganati, G. Olivieri, M.E. Russo, P. Salatino, A. Marzocchella, Continuous xylose fermentation by Clostridium acetobutylicum – Kinetics and energetics issues under acidogenesis conditions, Bioresour. Technol. 164 (2014) 155–161. [28] A. Procentese, F. Raganati, G. Olivieri, M.E. Russo, P. Salatino, A. Marzocchella, Continuous lactose fermentation by Clostridium acetobutylicum – Assessment of solventogenic kinetics, Bioresour. Technol. 180 (2015) 330–337. [29] F. Raganati, A. Procentese, G. Olivieri, P. Salatino, A. Marzocchella, Biobutanol production from hexose and pentose sugars, Chem. Eng. Trans. 38 (2014) 193–198.

competitive energy demand. The thermal desorption process is a potential process for butanol recovery operation. 4. Conclusions Adsorption tests were carried out using Amberlite XAD-7 as adsorbent material. After the adsorption step the loaded Amberlite was exposed to two different desorption tests – chemical desorption with methanol and thermal drying/desorption. The stability of Amberlite XAD-7 bed with respect to butanol capture and concentration was provided by carrying out the adsorption–desorption cycle ten times. The key results of this study are:

• amberlite XAD-7 was characterized by high adsorption capacity and

• • •

selectivity towards butanol. The adsorbed butanol concentration was 102.1 mg/g and the mass ratio among butanol, acetone, ethanol, acetic and butyric acid under adsorbed state was 1:0.167:0.041:0.138:0.209 when using a solution of 13 g/L of butanol, 5.8 g/L of acetone, 1.6 g/L of ethanol, 6 g/L of acetic acid and 9 g/L of butyric acid; adsorbed butanol was recovered as a high butanol concentration solution according to thermal (butanol concentration higher than 800 g/L) and chemical desorption processes (butanol concentration in methanol solution higher than 20 g/L, that is about 1.7 times the concentration in the stream used to saturate the resin). amberlite XAD-7 adsorption capacity was as high as 97% under repeated process cycle for both the recovery techniques investigated. the energy demand to concentrate butanol from broth-like solution (about 13 g/L butanol) is about 13 MJ/kgB, a fraction of the energy content of the recovered butanol (36 MJ/kgB).

Acknowledgements The authors thank the European Union’s Horizon 2020 research and innovation program for the financial support to the project Waste2Fuels (grant agreement No 654623). References [1] N. Abdehagh, F.H. Tezel, J. Thibault, Separation techniques in butanol production: challenges and developments, Biomass Bioenerg. 60 (2014) 222–246. [2] V.I. Águeda, J.A. Delgado, M.A. Uguina, J.L. Sotelo, Á. García, Column dynamics of an adsorption–drying–desorption process for butanol recovery from aqueous solutions with silicalite pellets, Sep. Purif. Technol. 104 (2013) 307–321. [3] D. Cai, H. Chen, C. Chen, S. Hu, Y. Wang, Z. Chang, Q. Miao, P. Qin, Z. Wang, J. Wang, T. Tan, Gas stripping-pervaporation hybrid process for energy-saving product recovery from acetone-butanol-ethanol (ABE) fermentation broth, Chem. Eng. J. 287 (2016) 1–10. [4] H.R. Cascon, S.K. Choudhari, G.M. Nisola, E.L. Vivas, D.J. Lee, W.J. Chung, Partitioning of butanol and other fermentation broth components in phosphonium and ammonium-based ionic liquids and their toxicity to solventogenic clostridia, Sep Purif Technol. 78 (2011) 164–174.

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