ABE fermentation products recovery methods A review.pdf

ABE fermentation products recovery methods—A review
Anna Kujawska a,n
, Jan Kujawski b
, Marek Bryjak b
, Wojciech Kujawski a
a
Nicolaus Copernicus University in Toruń, Faculty of Chemistry, 7 Gagarina Str., Toruń, Poland
b
Wroclaw University of Technology, Chemical Faculty, 27 Wybrzeże Wyspiańskiego Str., Wrocław, Poland
a r t i c l e i n f o
Article history:
Received 25 February 2014
Received in revised form
11 March 2015
Accepted 3 April 2015
Keywords:
Butanol production
Separation techniques
Butanol recovery
Pervaporation
a b s t r a c t
Butanol has a great potential as a biofuel and to date a lot of research has been done both in terms of
more efﬁcient butanol production as well as in developing product recovery methods. Many of them
deal with separation techniques which can be used for selective recovery of acetone, n-butanol and
ethanol from model solutions and fermentation broths. This work is a review of techniques used for ABE
recovery, such as distillation, adsorption, gas stripping, liquid–liquid extraction, pertraction, membrane
distillation, sweeping gas pervaporation, thermopervaporation and vacuum pervaporation. Advantages
and disadvantages of using particular methods, examples of applications and integrated processes are
also described.
& 2015 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
1.1. n-Butanol as a biofuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
1.2. ABE fermentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649
2. Separation techniques for ABE fermentation products recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
2.1. Distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
2.1.1. Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
2.1.2. Gas stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
2.1.3. Liquid–liquid extraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652
2.1.4. Pertraction (membrane extraction). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
2.1.5. Reverse osmosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
2.1.6. Membrane distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653
2.1.7. Pervaporation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654
2.2. Integration of n-butanol fermentation with various removal techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658
3. Final remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659
1. Introduction
1.1. n-Butanol as a biofuel
The biofuels production is nowadays one of the main app-
roaches in developing a sustainable economy [1]. According to
data presented by U.S. Energy Information Administration [2] total
World biofuels production in 2001 was equal to 54,511 m3
day 1
,
whereas in 2011 production of biofuels reached a value of
304,587 m3
day 1
and 302,290 m3
day 1
in 2012. This means that
production of biofuels increased during 10 years by more than
ﬁve times.
n-Butanol has been in production since 1916, mostly as a
solvent feedstock. Nowadays, after decades of stagnation, new
applications for n-butanol are becoming popular, such as a fuel
enhancer and basic feedstock for chemical industry [3]. n-Butanol
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/rser
Renewable and Sustainable Energy Reviews
http://dx.doi.org/10.1016/j.rser.2015.04.028
1364-0321/& 2015 Elsevier Ltd. All rights reserved.
n
Corresponding author. Tel.: þ48 56 611 43 15; fax: þ48 56 654 24 77.
E-mail address: arozicka@interia.pl (A. Kujawska).
Renewable and Sustainable Energy Reviews 48 (2015) 648–661

is 4-carbon alcohol that can be produced by fermentation of the
biomass [4]. Comparing with methanol and ethanol (Table 1), n-
butanol is a more complex alcohol, possessing several advanta-
geous characteristics: higher heating value, lower volatility, less
ignition problems, higher viscosity and is safer for distribution [4].
Moreover, n-butanol can be blended with petrol at any ratio.
Furthermore, using butanol as a fuel enables reduction of NOx
emission and soot creation in exhaust gases [3,4].
Ni and Sun [9] listed eleven Chinese companies producing n-
butanol by Clostridium strains. Moreover, two other companies
were under construction, one was designed and another two are
planned. Such significant development of ABE production plants is
attributed to a very high n-butanol demand in China [9]. In 2012,
Saudi Kayan, Sadara Chemical and Saudi Acrylic Acid Company
(SAAC) started to cooperate in organization of a new company—
The Saudi Butanol Company (Saudi Arabia). The company will be
the first one producing n-butanol in the Middle East. The projected
plant will be situated at Tasnee Petrochemicals Complex in Jubail
Industrial City (Saudi Arabia). The factory will be operated by
Tasnee and start of n-butanol production is planned in 2015. The
designed capacity of the plant is 330,000 t of n-butanol and
11,000 t of iso-butanol annually [10]. SGBio Renewable (joint
venture of GranBio (Brazil) and Rhodia (Belgium)) plan to build a
biomass-based n-butanol installation in Brazil [11]. Biobutanol will
be produced from bagasse and sugar cane straw. A pilot plant is
planned to be built in 2015 to test their technologies, and based on
the results of that research, a commercial scale plant will be built
later on [12]. In VITO Company (Belgium) has been opened pilot
installation for demonstration of acetone–butanol–ethanol fer-
mentation integrated with in situ butanol removal technology by
pervaporation [13]. The project realised within this study is called
Demonstration of In Situ Product Recovery (ISPR) to improve the
fermentation processes productivity (DemoProBio). The demon-
strated pilot plant will be operated in 50 and 150 L scale to assess
energy requirements and process efficiency in ABE fermentation
products recovery [13].
The biggest biobutanol facilities in the world, in operation or
under construction, are marked in Fig. 1.
1.2. ABE fermentation
n-Butanol can be produced during fermentation process per-
formed by bacteria strain. The most popular strains used in n-
butanol production are Clostridium strains such as Clostridium
acetobutylicum, Clostridium saccharobutylicum, Clostridium beijer-
inckii and Clostridium saccharoperbutylacetonicum [14–16]. The
comprehensive description of metabolism during acetone–buta-
nol–ethanol fermentation can be found elsewhere [16,17].
The main problem associated with the ABE fermentation by
bacteria is the self-inhibition of the process due to n-butanol
toxicity to the culture. Mentioned toxicity of solvent to the culture
and nutrient depletion during long time fermentation processes
are two main factors caused premature termination of the
fermentation [14]. Otherwise, bacterial n-butanol fermentation
could be more efficient due to gene modification of bacteria
already used in n-butanol production or by utilization of another
bacteria strain, more tolerant to produced product. Moreover,
fermentation process could be improved if new and cheaper
substrates, such as hydrolysed lignocellulosic biomass, would be
utilized. Additionally, reduction of the by-products production and
Nomenclature
ABE acetone, n-butanol, ethanol
AGMD air gap membrane distillation
Ai, Aj molar or weight fractions of components i and j in
permeate [g g 1
] or [mol mol 1
]
Bi, Bj molar or weight fractions of components i and j in
feed [g g 1
] or [mol mol 1
]
DCMD direct contact membrane distillation
Dp pore diffusion coefficient [m2
s 1
]
EBA expanded bed adsorption
ETBE 2-ethoxy-2-methylpropane (ethyl tert-butyl ether)
IL ionic liquid
Jt total flux in pervaporation [g m 2
h 1
]
MAVS membrane assisted vapour stripping
MD membrane distillation
MPCs mesoporous carbons
MTBE 2-methoxy-2-methylpropane (methyl tert-
butyl ether)
NMP n-methyl-2-pyrrolidone
PDMS poly(dimethylsiloxane)
PDMSM poly(dimethylsilmethylene)
PE polyethylene
PEBA poly(ether block amide)
PP poly(propylene)
PPO poly(dimethylphenyleneoxide)
PSf polysulfone
PSI Pervaporation Separation Index [kg m 2
h 1
]
PTMSP poly[1-(trimethylsilyl)-1-propyne]
RO reverse osmosis
SGMD sweeping gas membrane distillation
SGPV sweeping gas pervaporation
TAME 2-methoxy-2-methylbutane (tert-amyl methyl ether)
TAEE 2-ethoxy-2-methylbutane (tert-amyl ethyl ether)
THF tetrahydrofuran
TPV thermopervaporation
VMD vacuum membrane distillation
VOC volatile organic compounds
VPV vacuum pervaporation
β separation factor in pervaporation [–]
Table 1
Comparison of fuels [5–8].
Parameter Petrol Diesel Methanol Ethanol n-Butanol
Energy density [MJ L 1
] 32 39–46 16 19.6 27–29.2
Vapour pressure at 20 1C [kPa] 0.7–207 o0.07 12.8 7.58 0.53
Motor octane number 81–89 – 97–104 102 78
Boiling point [1C] 27–225 180–343 64.5–65 78–78.4 117–118
Freezing point [1C] o 60 40 to 9.9 97 to 97.6 114 to 114.5 89.3 to 89.5
Air-fuel ratio 14.6 – 6.5 9.0 11.2
Density at 20 1C [g mL 1
] 0.74–0.80 0.829 0.787 0.785 0.810
A. Kujawska et al. / Renewable and Sustainable Energy Reviews 48 (2015) 648–661 649

application of advanced and sterile fermentation or downstream
technology could positively affect fermentation process efficiency
[3]. The highest n-butanol productivity by the strain fermentation
reported in literature is 3.0 wt% [4].
Qureshi and Blaschek [15] described that C. beijerinckii BA101
strains can produce solvent in the concentration range of 27–
29 g L 1
. Properties of bacteria were examined in terms of impact
of fermentation substrates and products inhibition to solvents
production performance. It was shown that supplementing the
fermentation medium with sodium acetate enhances production
of solvents up to 33 g L 1
. Pervaporation was combined with fed-
batch reactors and applied as a separation technique for fermenta-
tion products recovery. Solvents production after applying recov-
ery technique was 165 g L 1
[15].
Mariano et al. [18] described vacuum fermentation as a simple
technique during which the desired product is removed due to
vacuum applied directly to bioreactor. Products boil off at the
temperature of fermentation and in subsequent step are recovered
by condensation. Using this approach the low concentration of
fermentation products is maintained in bioreactor during fermen-
tation process and toxic impact of products to the microbes is
minimalized. The technique was already successfully used in
ethanol fermentation [19]. Mariano and co-workers [18] per-
formed a research using vacuum fermentation to produce ABE
fermentation products. Authors evaluated the technical feasibility
of vacuum technique application in acetone–butanol–ethanol
fermentation as well as the influence of vacuum on the fermenta-
tion performed by C. beijerinckii and products recovery rate. The
performance of vacuum process was higher than for standard
batch fermentation (production of 106.0 g vs. 80.6 g of n-butanol,
and 132.4 g vs. 110.1 g total ABE, respectively). Moreover, applica-
tion of vacuum for product recovery from fermentation resulted in
a decrease of fermentation time, maximal utilization of glucose,
and superior cell growth, and greater acetone, butanol, ethanol
production comparing with control batch fermentation. It was also
found that fermentation intermediates did not affect n-butanol
concentration in the removed condensate stream [18].
Maddox et al. [20] tested possible inhibitory effects of high salt
and sugar concentrations on the ABE fermentation process. Authors
[20] found out that sugar concentrations up to 200 g L 1
can be
fermented, however that salt concentrations greater than 30 g L 1
negatively affect bacterial growth.
2. Separation techniques for ABE fermentation products
recovery
Several techniques have been suggested for acetone, butanol
and ethanol recovery from fermentation broth: distillation [21–
24], adsorption [1,25–27], freeze crystallization [28], gas stripping
[14,20,29–32], liquid–liquid extraction [33,34], pertraction [35],
reverse osmosis [28], membrane distillation [36–38], thermoper-
vaporation [39], sweeping gas pervaporation [40] and vacuum
pervaporation [41–52].
2.1. Distillation
Distillation is one of the well-known separation techniques in
which separation occurs due to the difference of volatilities of
separated components. When a mixture containing substances of
various volatilities is brought to boiling, the composition of the
vapours released will be different than content of solvents in the
boiling liquid. There are several possible modes of distillation:
continuous flash distillation, batch distillation, fractional distilla-
tion and steam distillation [53].
Aqueous acetone–butanol–ethanol mixture is a complex sys-
tem, in which water–organic azeotropic mixtures can be formed
during distillation (Table 2).
Thanks to heterogeneous water-n-butanol azeotrope, a simple
two-column distillation system can be used and no additional
compound has to be added to separate mixture [55]. Conventional
distillation for recovery of ABE fermentation products from batch
fermentator was described by Roffler et al. [22]. Acetone, n-
butanol and ethanol are heated to 100 1C by heat exchange and
are removed from the broth by stream of vapours [22]. Obtained
vapours contain about 70 wt% of water and 30 wt% of AcO, BuOH
and EtOH. Subsequently, vapours are separated in series of four
distillation columns. In the first column, operating at 0.7 atm
pressure, about 99.5 wt% of acetone is removed, whereas residual,
bottoms products of the first column are transported to so-called
ethanol column, operating at 0.3 atm pressure. 95 wt% ethanol is
Table 2
Azeotropes during distillation of ABE–water mixture [21,54,55].
System Azeotrope Temperature of
azeotrope [1C]
Water content in
azeotrope [wt%]
Water—n-
butanol
Heterogeneous 91.7–92.4 38.0
Water—
ethanol
Homogeneous 78.1 4.4
Fig. 1. Butanol production plants in the world.
A. Kujawska et al. / Renewable and Sustainable Energy Reviews 48 (2015) 648–661
650

obtained in this step. Subsequently, the bottom products of
ethanol column and overhead streams are redirected to decanter,
where water and n-butanol are separated. The water phase, with
ca. 9.5 wt% of n-butanol content, is transported to water stripper,
whereas the n-butanol rich phase (with ca. 23 wt% water content)
is redirected to n-butanol stripper. In the n-butanol stripper
99.7 wt% n-butanol is obtained [22].
Mariano et al. [23] described the flash fermentation, i.e.
continuous fermentation with integrated ABE recovery. In this
design, a bioreactor worked at atmospheric pressure, whereas
broth was continuously circulated to a vacuum chamber. In the
vacuum chamber acetone, n-butanol and ethanol were boiled off
and condensed. Proposed technology allowed to produce 30–
37 g L 1
of n-butanol [23].
Luyben [24] reported pressure-swing azeotropic distillation as
a method to separate compounds. In this technique two columns,
operating at various pressures, were used for separation of liquid
mixtures. In such module no additional compounds were required.
The high-purity product streams were removed, whereas the
streams of the composition near azeotropic one, were recycled.
It was also pointed out that higher pressure changes can markedly
shift the azeotrope composition [24].
During n-butanol recovery by distillation, most of the energy
consumption originates from the evaporation of the water in the
feed. Additionally, a binary n-butanol–water azeotrope is obtained
at 92.7 1C. Conversion of a feed containing 20 g L 1
n-butanol into
an azeotropic mixture at 1 atm leads to a selectivity of 72 [56].
Matsumura et al. [21] provided analysis of energy requirement
for n-butanol recovery by distillation. n-Butanol concentration
before distillation was 0.5 wt%. Energy requirement to obtain
99.9 wt% of n-butanol by distillation was 79.5 MJ kg 1
. Vane
et al. [57] described that energy requirement to produce 99.5 wt
% n-butanol is 14.5 MJ kg 1
by traditional distillation-decanter
method. Green [58] claimed that distillation is a robust and proven
process to be used for ABE fermentation products recovery, but
this technique is energy intensive. It was stated that to produce 1 t
of solvents, about 12 t of steam is necessary. The author [58]
suggested that improvements can be made to traditional distilla-
tion but investigation of nonconventional methods should be also
performed to reduce ABE production costs.
Distillation is nowadays the most popular technique used in
industry for ABE fermentation product recovery. However, this
technique possesses several disadvantages such as high investment
costs, high energy consumption and low selectivity [28]. Due to this
fact other products recovery techniques are being investigated.
2.1.1. Adsorption
Adsorption is described as a process in which particles from a
liquid or gas mixture are preferentially attached on a solid surface
[59]. Levario and co-workers [25] investigated adsorption of
ethanol and n-butanol on mesoporous carbons (MPCs) with sur-
face areas ranging from 500 to 1300 m2
g 1
. It was found that n-
butanol was adsorbed more efficiently compare to ethanol on each
of tested mesoporous carbons. It was also found that capacity of
alcohol adsorbtion increased with an increase of adsorbents sur-
face area. Moreover, applied mesoporous carbons were thermally
and chemically stable during performed measurements [25].
Lin et al. [1] applied macroporous adsorption resin (KA-I) with a
crosslinked polystyrene framework as adsorbent for n-butanol
removal from acetone-n-butanol–ethanol–water quaternary mixture
at various concentrations of organics. Ratio of organic compounds
equal to 3:6:1 of acetone, n-butanol and ethanol, respectively was
maintained constant. KA-I resin selectively adsorbed n-butanol,
whereas acetone and ethanol were less adsorbed compounds. It was
reported that increase of temperature enhanced adsorption capacity
and rate of n-butanol removal [1]. The effective pore diffusion
coefficients (Dp) at 10 1C and 37 1C were 0.251 10 10
m2
s 1
and
4.31 10 10
m2
s 1
, respectively. Additionally, the results obtained
fitted well with the Langmuir isotherm equation [1]. Authors found
that effective Dp is temperature dependent, but uninfluenced by initial
n-butanol content. The total maximal amount of n-butanol adsorbed
per mass of wet resin up to saturation of KA-I resin was found to be
139 mg g 1
at 10 1C and 304 mg g 1
at 37 1C [1]. Some other
adsorbents reported in literature with n-butanol adsorption capacities
are: high silica zeolite CBV28014 (116.0 mg g 1
) [26], ZSM-5
(160.8 mg g 1
) [60] and silicalite (97.0 mg g 1
) [61].
Sharma and Chung [27] described development of a new
zeolite to be utilized in preparation of mixed matrix membranes.
The authors [27] also presented adsorption potentials of the
mentioned materials during n-butanol recovery. The highest
obtained capacity towards butanol adsorption of MEL6 zeolite
type material was 222.24 mg g 1
at 30 1C.
Oudshoorn et al. [26] investigated n-butanol adsorption by
three various commercial high silica zeolites (CBV28014, CBV811C-
300 and CBV901) in the presence of ethanol and acetone in
aqueous mixtures and fermentation broth. The surface areas of
the silica zeolites were equal to 400, 620 and 700 m2
g 1
, whereas
pore volumes of tested particles were equal to 0.19, 0.24 and
0.50 cm3
g 1
, respectively. CBV901 possesses the highest adsorp-
tion capacity for n-butanol among all zeolites tested in this study,
whereas CBV28014 has the highest affinity towards n-butanol at
the organic component content in water below 2 g L 1
. It was also
found that compounds were competitively adsorbed following the
order: n-butanol4acetone4ethanol.
Wiehn et al. [62] applied expanded bed adsorption (EBA)
method for the in situ removal of BuOH from ABE fermentation
broth. Macroporous hydrophobic poly(styrene-codivinylbenzene)
resin was used in this study as butanol adsorbent. After 38.5 h of
process 27.2 g L 1
and 40.7 g L 1
of butanol and total solvents were
produced, respectively. Efficiency of total solvent production was
improved in expanded bed adsorption method 2.3-fold, compared
to traditional batch fermentation. At the same time, butanol
production was increased 2.2-fold. Authors [62] recovered ca. 81%
of butanol from fermentation broth using EBA technique recovery.
Liu et al. [63] used KA-I cross-linked polystyrene framework
resin to recover butanol from fermentation broth. KA-I was chosen
due to its good adsorbing properties towards butanol, butyrate,
and acetone and high selectivity. The authors [63] developed an
operation combining biofilm reactor with simultaneous product
recovery by the KA-I resin. Obtained solvent productivity in such a
module was 1.5 g L 1
h 1
and yield of solvent production was
0.33 g g 1
. It was also shown that co-adsorption of acetone by the
KA-I resin caused improvement of the fermentation process
performance [63].
Although adsorbents used in adsorption technique possess
high selectivity towards butanol over water [26], there are several
problems during ABE fermentation products recovery by adsorp-
tion. One of them are difficulties in desorption of organic com-
pound previously adsorbed on the sorbent—several separation
methods should be used to realise this process. Additionally,
bacteria can adhere to the adsorbent and decrease the adsorption
efficiency, especially if the adsorbent is recycled [64,65].
2.1.2. Gas stripping
Gas stripping is a separation method which enables selective
removal of volatile components from ABE fermentation broth
[14,29–32]. In this technique gas is sparged into the fermentor
and volatiles are condensed and subsequently recovered from the
condenser. Application of this technique is possible due to the
volatile properties of the ABE.

Ezeji et al. [29] tested the influence of various parameters,
such as presence of acetone and ethanol, gas recycle rate and
bubble size, on performance of ABE recovery from fermentation
broth. It was found that application of sparger gas stripping mode
resulted in creation of overmuch amounts of foam in bioreactor,
which caused necessity of addition of more antifoam to compare
with impeller module. The consequence of antifoam addition is
reduced production of the fermentation products, which is
explained as a toxic effect of antifoam to microbes. Authors
found that gas recycle rates of 80 cm3
s 1
and constant gas
stripping rate of 0.058 h 1
are sufficient to maintain the n-
butanol concentration below toxic levels during the run of the
ABE fermentation. Ezeji and co-workers [29] demonstrated that
bubble sizes below 5.0 mm did not affect the stripping rate of n-
butanol under the experimental conditions used in this study. It
was also found that presence of acetone, and ethanol had no
influence on n-butanol removal rate. Additionally, gas bubble size
in diameter ranging from 0.5 mm to 5.0 mm was recommended
to obtain good mass transfer and to overcome problems with
overmuch foam creation in gas stripping process.
Ezeji and co-workers [14] examined impact of gas-stripping on
the in situ recovery of ABE fermentation products directly from
batch reactor. An integrated batch fermentation experiment pro-
duced total ABE of 23.6 g L 1
and it was higher than for the non-
integrated process (17.7 g L 1
). The authors [14] proved that gas-
stripping intensifies the selective recovery of acetone, butanol and
ethanol from the fermentation broth and encourages effective
assimilation of acids produced by the culture for conversion into
solvents. Also it was shown that acids were not removed from the
fermentation broth during gas stripping and the bacteria strain
was not negatively affected by this removal method.
Park et al. [30] employed a gas-phase-continuous immobilized
cell reactor–separator concept (ICRS) for n-butanol production
from ABE fermentation. Authors compared two modes of gas
stripping reactor: immobilized cell reactor (ICR) and immobilized
cell reactor separator (ICRS). In ICRS mode greater glucose con-
sumption rate and higher n-butanol productivity could be
obtained. The average glucose conversion was improved by
54.7% (from 19.63 to 30.36 g L 1
) due to application of the product
separation method [30].
Qureshi and Blaschek [31] reported that the adoption of gas
stripping allows reducing n-butanol inhibition and due to this fact
the application of gas stripping coupled with fermentation broth
results in improving total solvent productivity and yield. Enhanced
yield of fermentation can be obtained thanks to the fact that gas
stripping does not remove intermediate products of the ABE
production process. In conclusion, gas stripping removing n-
butanol (and thus reducing fermentation product toxicity) can be
performed within the fermentor without any negative influence
on bacterial culture. Moreover, concentrated sugar solutions can
be used during gas stripping coupled with fermentor [31].
Setlhaku et al. [32] tested properties of fermentor containing C.
acetobutylicum ATCC 824 strain coupled with gas stripping set-up.
Experiments were carried out at 35 1C, whereas ABE vapours were
collected at 2 1C using 50:50 vol% of ethyl glycol–water mixture.
Experiments were performed at a gas (nitrogen) circulation rate in
the range of 4.8–6.6 L min 1
. Authors obtained maximum perfor-
mance of gas stripping equal to 72.9 g L 1
of acetone, n-butanol
and ethanol at a third fed-batch fermentation. After 272 h of
fermentation gas stripping was started and at that time glucose
and butyric acid concentration in the reactor were equal to 0.2 and
1.7 g L 1
, respectively.
Liao et al. [66] tested influence of agitation speed, flow rate and
type of non-polar gases on the performance of gas stripping.
Stripping rate of butanol was proportional to butanol content in
feed and a decrease in butanol selectivity was observed with the
increasing butanol concentrations up to 0.01 g cm 3
. It was
explained in terms of thermodynamics that more inert gas was
dissolved at higher butanol concentration in feed. Higher quantity
of gas dissolved in the solution resulted in a decrease of butanol
activity. The authors [66] concluded that the best way for improv-
ing butanol recovery with gas stripping method is to perform
process at high superficial velocity of gas bubbles, what results in
the lower resistance on the liquid side. Among tested gases (N2, O2
and CO2), nitrogen was recommended as the best one for butanol
recovery with gas stripping method (mass transfer coefficient
equal to 17.4 106
s 1
) [66].
The gas-stripping process possesses several advantages over
other removal techniques, such as a simplicity and low cost of
operation and its efficiency is not disturbed by fouling or clogging
due to the presence of biomass [14]. Moreover, gases produced
during the fermentation (CO2 and H2) can be used for ABE
products recovery by gas stripping. Furthermore, only volatile
products are removed from fermentation broth and due to this
fact the reaction intermediates (acetic acid and butyric acid) are
not removed from the fermentation broth and are converted
almost entirely into ABE [20].
One of disadvantages is that tiny bubbles, produced in gas
stripping, create excessive amounts of foam in a bioreactor. Such a
process results in the necessity of addition of an antifoam agent,
which can be toxic to bacteria. This, in turn, results in overall lower
productivity of ABE fermentation [29].
2.1.3. Liquid–liquid extraction
Liquid–liquid extraction is a method used to extract a dissolved
substance from liquid mixture in a certain solvent, by another
solvent [67]. Eckert and Schügerl [33] described application of
continuously operated membrane bioreactor combined with a
four-stage mixer–settler cascade in n-butanol recovery. BuOH
was selectively extracted from the cell-free cultivation medium
by butyric acid saturated n-decanol, and the n-butanol-free
medium was re-fed into the reactor. Under steady-state conditions
n-butanol concentration of 8 g L 1
and n-butanol productivity of
0.51 g L 1
h 1
were obtained. Unfortunately, the addition of n-
decanol to the reactor strongly reduces the fermentation process
productivity due to the poisoning of the cells. Due to this, contact
of the cells with the n-decanol phase should be eliminated.
Authors [33] checked mass of the cells before and after the
experiment. It was shown that the mass of cells decreased after
extraction. Such a phenomenon caused productivity decrease of
ABE in the second cycle of experiments. Application of good
extractants, such as n-decanol, to ABE fermentation broth for
direct removal of n-butanol can cause destruction of bacteria
strains in fermenter. To overcome this negative impact on bacteria,
Evans and Wang [34] used combination of toxic decanol and
nontoxic oleyl alcohol. Authors convinced that up to 40 vol%
decanol in oleyl alcohol is nontoxic to bacteria growth. Increase
of intermediate fermentation products concentration was
observed at higher pH. At constant pH value equal to 4.5 an
increase in n-butanol production with addition of decanol was
observed. Approximately 90 mM of n-butanol was produced in
system without addition of decanol, ca. 150 mM n-butanol at
0.3 vol% of decanol and approximately 40 mM of n-butanol were
obtained when 0.4 vol% of decanol was present in system [34].
Kurkijärvi et al. [68] applied non-biocompatible solvents (1-
heptanol, 1-octanol and 1-decanol) during continuous extraction
of ABE fermentation products in dual extraction process with
solvent regeneration. Distribution coefficients of butanol recovery,
obtained during experiments performed at 37 1C, were equal to
11.26, 9.95 and 7.17 for 1-heptanol, 1-octanol and 1-decanol,
respectively. The authors [68] claimed that with this method the
652

energy consumption of the ABE fermentation product recovery can
be lowered to less than 4 MJ kg 1
.
Kurkijärvi and Lehtonen [69] described a dual extraction method
utilizing petrol components as extraction solvents in ABE fermenta-
tion. This dual extraction method contains two extraction columns.
In the first column nonbiocompatible solvents were utilized to
extract effectively ABE products, whereas in the second column
traces of the toxic solvent were removed from the broth to make it
biocompatible. After the extractions the fermentation broth was
recycled back to the reactor, thanks to that unfermented nutrients,
reaction intermediates, and remaining products could be reutilized.
To avoid migration of microbes to extraction column, immobilization
and filtration steps were added to the process. The authors [69]
claimed that product mixture of this process (ABE removed from
broth and extractants) could be utilized as a petrol additive without
purification steps. Simulation performed in this study showed that
ETBE and MTBE were the most effective solvents for butanol
recovery, followed by TAME and TAEE. However, ABE concentration
in the end product was low (7.6 kg of butanol in 477.4 kg total
amount of product, i.e. less than 16 g kg 1
) [69].
Stoffers and Gorak [70] tested efficiency of butanol recovery by
ionic liquid, 1-hexyl-3-methylimidazolium tetracyanoborate, dur-
ing continuous multi-stage extraction in mixer–settler unit. The
authors [70] obtained selectivity of butanol recovery towards
water in the range of 48–89, whereas distribution coefficient for
the tested system was 5.2–6.5. Moreover, extraction model, based
on NRTL parameters from ternary mixture experimental data, was
proposed. Based on the results it was stated that in an equilibrium
approach of the multi-stage extraction model there is no need to
model individual stage efficiency [70].
Comparing to other separation techniques, high capacity of the
extractant and high selectivity of n-butanol/water separation can
be obtained. The main disadvantage of using direct extraction in
fermentation products recovery is the creation of emulsions and
the extractant fouling. Such phenomena can result in problems
with phase separation and consequently in significant contamina-
tion of aqueous streams with chemicals [71,72].
2.1.4. Pertraction (membrane extraction)
Pertraction can be described as a liquid–liquid extraction
technique in which a porous membrane is placed between the
two phases [73]. Pertraction is a membrane process based on the
same separation mechanism as extraction [74], where both extrac-
tion and stripping of the solute are realized in one unit [75].
Membrane extraction requires the installation of membrane area,
which separates extracting liquid from the extractant.
Grobben et al. [35] applied in-line solvent recovery for direct
removal of acetone, n-butanol and ethanol from potato waste.
Authors used C. acetobutylicum DSM 1731 strain to produce ABE
broth. Fermentation broth was coupled with two modes of solvents
recovery: direct pertraction and microfiltration combined with
pertraction. Pertraction was performed using polypropylene fibre
membranes and a mixture of 50:50 (vol%) of oleyl alcohol and
decane was pumped through the fibres. In the second tested mode a
cylindrical separation chamber containing a rotating cartridge
equipped with polysulphone microfiltration membrane was applied.
Compared to standard fermentation, application of pertraction
resulted in increased productivity of ABE by 60% to 1.0 g L l
h 1
,
whereas the product yield based on dry weight was improved from
0.13 g g 1
to 0.23 g g 1
. Experiments with fermentation coupled
with microfiltration and pertraction showed that the initial ABE
recovery through the membrane (0.55 g L l
h 1
) was greater than
the ABE productivity (0.38 g L 1
h 1
). Such efficiency of the process
allowed maintaining n-butanol concentration below the toxic level
for a extended period of time comparing with standard fermentation.
Total production of ABE was equal to 27 g L 1
and product yield,
based on quantity of consumed sugars, was equal to 32 wt% and was
higher than for the control fermentation broth.
Qureshi et al. [73] investigated pertraction mode coupled directly
with fermentor at 35 1C. Silicone membrane as selective boundary
and oleyl alcohol as extractant were used. Butanol production in the
first cycle was 8.89 g L 1
, whereas in the second operation cycle
butanol productivity of 10.29 g L 1
was obtained. Although recovery
of butanol was efficient, acetone removal from fermentation broth
was poor (1.62 g L 1
in the first cycle) [73]. In another work Qureshi
and Maddox [76] used oleyl alcohol as an extractant for recovery of
acetone, n-butanol and ethanol. The solvents were produced by
Clostridium strains from lactose. Butanol productivity was equal to
2.89 g L 1
, whereas acetone and ethanol production efficiencies
were 3.25 and 1.87 g L 1
, respectively.
Pertraction possesses some limitations such as lower mass-
transfer coefficients compared with liquid–liquid extraction and
instability of hollow fibre modules in contact with solvent [71]. On
an industrial scale, problems with extraction of membrane solvent
may occur, due to the relatively high viscosity of extractants. Such
difficulties resulted in pressure losses and mass transfer limita-
tions in the solvent phase [72].
The major advantage of the pertraction method is that disper-
sion of the extractant in the solvent phase is unnecessary. Using
membrane pertraction it is possible to connect selective mem-
brane properties with the capacity of extractant [72]. Application
of membrane as a barrier in pertraction mode minimizes passage
of extractant into the aqueous phase and alleviates some common
problems of the liquid–liquid extraction process, such as toxicity of
extractant to the cells [73].
2.1.5. Reverse osmosis
Reverse osmosis (RO) is a membrane based technology com-
monly applied in desalination of water and production of potable
water [77]. In RO semi-permeable membranes separate a feed
solution into two streams: permeate (purified water) and con-
centrate (solution with salts and retained compounds) [77]. Poly-
amide membranes were described as good materials for BuOH
recovery in RO (rejection rate r85%). Garcia et al. [78] obtained
rejection rates in the range of 98% and the optimal rejection of
BuOH in the ferment liquor occurred at recoveries of 20–45%. Flux
varied in the range 0.05–0.60 dm3
m 2
min 1
[78].
Ito et al. [79] patented a method to separate highly pure
butanol from a butanol-containing solution. The method assumes
that in the first step of separation a nanofiltration of fermentation
broth is performed. In a subsequent step, the filtered solution is
sent to reverse osmosis module. Retentate contains two phases
system enriched in butanol. The last step is recovery of butanol
rich phase. This technique allows to obtain butanol–water mixture
containing 80% of BuOH.
Diltz et al. [80] utilized reverse osmosis (RO) method for a post-
treatment of an anaerobic fermentation broth. Experiments were
performed at 25 1C using six organic model compounds: ethanol,
butanol, butyric acid, lactic acid, oxalic acid, and acetic acid.
Efficiency of butyric acid, lactic acid, and butanol rejection was
greater than 99% at a pressure of 5515.8 kPa, whereas acetic acid,
ethanol and oxalic acid were rejected with efficiency in the range
of 79–92% at a pressure of 5515.8 kPa. The rejection of organic
components was improved when the fermentation broth was used
as the feed stream, comparing with RO experiments performed for
each component individually [80].
2.1.6. Membrane distillation
Membrane distillation (MD) is a process in which a micropor-
ous, hydrophobic membrane is applied to separate aqueous

solutions at different temperatures [81]. Membrane distillation
process is similar to conventional distillation: requires heating of
the feed solution in order to obtain the necessary latent heat of
vaporization and MD is based on the vapour/liquid equilibrium
[82]. The temperature difference between both sides of micropor-
ous membrane results in a vapour pressure difference. Thanks to
that vapour molecules are transported through the membrane
from higher vapour pressure to lower vapour pressure side of the
membrane. Membrane used in membrane distillation process
should be highly porous (of porosity higher than 70%). Moreover,
membrane wetting cannot occur and only vapours should be
transported through the pores of the membrane [81]. Five various
membrane distillation modes are described in literature: direct
contact (DCMD), vacuum (VMD), air gap (AGMD), sweeping gas
(SGMD) and osmotic (OMD) membrane distillation [36–38,82–87].
Most of membranes used in MD are manufactured from highly
hydrophobic polymers, like polyvinylidene fluoride (PVDF), poly-
tetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene
(PP) [36,37,81,82,86].
Gryta et al. [86] tested properties of batch fermentation
producing ethanol with membrane distillation recovery method.
The authors used porous capillary polypropylene (PP) membranes
to separate volatile organic compounds from fermentation broth,
which was supposed to increase productivity/efficiency of fermen-
tation process. The efficiency of fermentation broth combined with
membrane distillation was 0.4–0.51 (g EtOH)/(g of sugar) and the
production rate of 2.5–4 (g EtOH)/dm3
h.
Banat and Al-Shannag [36] investigated recovery of acetone, n-
butanol and ethanol from aqueous solutions by air gap membrane
distillation with PVDF membrane. The authors found out that n-
butanol was the most effectively removed compound. It was also
shown that temperature, air gap width and compounds concen-
tration affect the flux and selectivity of compounds recovery.
Fluxes of compounds increase with feed temperature increase.
Selectivity of acetone and ethanol recovery also increase with
temperature. n-Butanol selectivity decreased from 5.8 to 2.4 as the
coolant temperature increased from 10 1C to 30 1C. The best results
were obtained for the lowest tested cooling temperature. Accord-
ing to mass transfer equations, air gap width has also a significant
impact on membrane distillation process efficiency. Decrease of
air gap width increases the transport but lowers selectivity of
separation.
Banat et al. [37] applied air-gap membrane distillation for
separation of ethanol–water mixture by PVDF membranes. At
50 1C the highest obtained flux was 8.7 10 4
kg m 2
s 1
,
whereas selectivity remained between 2.5 and 3.1, within tested
concentration range 0.83–10.2 wt% of EtOH. In that work [37] a
mathematical model of transport was also proposed and experi-
mental data was used to evaluate the accuracy of the model. The
model including effect of temperature and concentration polar-
ization fitted well the experimental data. Cooling liquid flow rate
had no influence on obtained fluxes during MD experiments. It
was also found that an increase of feed temperature results in
increased flux as well as higher selectivity for all tested concen-
trations. The permeate flux was inversely proportional to the air
gap width [37].
Rom et al. [87] developed vacuum membrane distillation model
using AspenPlus software on the basis of the dusty gas model. The
experimental data obtained for poly(propylene) (PP) membrane of
0.2 μm pore size in contact with water–butanol mixture were used
as source of data for the determination of the component
permeance and for extrapolation of data for model. It was found
that implementation of the generated permeance functions in the
programming code resulted in a unit operation of the programme.
Authors [87] concluded that model showed good correlation with
experimentally obtained results.
2.1.7. Pervaporation
Pervaporation (PV) is a membrane separation technique for
separation of binary or multicomponent liquid mixtures [88].
Transport through membrane occurs owing to the difference in
chemical potentials between both sides of the membrane [89,90].
The difference in chemical potentials can be created by tempera-
ture difference (thermopervaporation—TPV), application of a
sweep gas on the permeate side (sweep gas pervaporation—SGPV)
and pressure difference (vacuum pervaporation—VPV) between
both sides of the membrane.
2.1.7.1. Thermopervaporation (TPV). Thermopervaporation (TPV) is
the least studied mode of pervaporation. Feed mixture is in direct
and continuous contact with the membrane selective layer,
whereas permeate is condensed on a cold wall at the
atmospheric pressure [91,92]. Transport in TPV can be facilitated
by increasing temperature difference and decreasing the distance
between the membrane and the cold wall [39,93].
Franken et al. [91] proposed polysulfone (PSf) membrane to be
used for ethanol recovery by thermopervaporation. Total flux
obtained during experiments with PSf membrane was equal to
14.4 g m 2
h 1
, whereas separation factor was 10, at 16.5 1C
difference and 35 wt% of ethanol in feed [91].
Borisov et al. [39] investigated recovery of n-butanol by
thermopervaporation using poly(1-trimethylsilyl-1-propyne)
(PTMSP) membranes. Authors used in their experiments plate-
and-frame flowthrough module with an air gap. Application of
thermopervaporation allows to decrease the dimension of the
separation units; and to increase the condensation temperature of
the permeate. Thanks to the mentioned advantages it is possible to
reduce energy consumption of the separation process.
Kujawska et al. [94] tested intrinsic properties of two commer-
cially available PDMS based membranes (Pervap 4060 and Perva-
tech) in thermopervaporative recovery of acetone, butanol and
ethanol from model aqueous solutions. Authors [94] obtained an
increase of organic component transport and selectivity coefficient
with increase of feed temperature during TPV experiments with
water–acetone and water–butanol mixtures. Permeance of ethanol
through both membranes was comparable, whereas significantly
higher water transport was obtained during TPV experiments with
Pervatech. Such a difference was attributed to different membrane
preparation conditions [94].
2.1.7.2. Sweeping gas pervaporation (SGPV). Sweeping gas per-
vaporation (SGPV) is pervaporation mode in which the permeant
partial pressure on the permeate side is decreased by sweeping
out the vapours with an inert gas stream. Hollow fibres are applied
in SGPV, which allows obtaining a large surface area per volume
ratio [95]. Nii et al. [95] developed a mass-transfer model for SGPV
through polymeric hollow fibre (HF) membranes. Basing on the
solution–diffusion–evaporation theory it was possible to assess
the permeation rate of alcohol across the membrane. Diffusional
resistance through the gas boundary film was accounted for in the
model [95]. The model was applied to test properties of a rubbery
hollow fiber membrane module by sweeping gas pervaporation at
304 K in contact with binary aqueous mixtures of ethanol and
isopropanol. PDMS hollow fibre membranes were used in SGPV
experiments and nitrogen was applied as the sweeping carrier gas.
It was found that water permeation occurred independently of the
alcohol permeation. The calculation of water flux using proposed
model was provided and it was found that at lower gas velocity
model did not fit well. Moreover, it was found that ethanol flux did
not vary at liquid flow rates in the range of 100–500 cm3
min 1
. It
was concluded that liquid film resistance did not occur under the
experimental conditions [95].
654

Plaza et al. [40] applied sweeping gas membrane pervaporation
for n-butanol recovery. Membranes prepared by gelation of an
ionic liquid-1-butyl-3-methylimidazoliumhexafluorophosphate
([bmim][PF6]) in the pores of polytetrafluoroethylene (PTFE)
hollow fibres were used in experiments. Partial flux of n-butanol
was equal to 1300 g h 1
m 2
at 500 ppm n-butanol content in
feed. Authors did not observe losses of IL during SGPV experi-
ments, but membrane selectivity decreased after several hours of
SGPV process.
2.1.7.3. Vacuum pervaporation (VPV). In vacuum pervaporation
mode a driving force is created by vacuum on the permeate side
of the membrane [88].
Liu et al. [41] provided a list of membranes used for ABE
fermentation products recovery by vacuum pervaporation: poly
(dimethyl siloxane) (PDMS), PDMS filled with silicate, ethylene
propylene diene rubber (EPDR), styrene butadiene rubber (SBR),
poly(methoxy siloxane) (PMS) and poly[-1-(trimethylsilyl)-1pro-
pyne] (PTMSP). PDMS can be also applied in sweep gas pervapora-
tion mode as well as porous propylene (PP) and porous
polytetrafluoroethylene (PTFE).
Vane [42] described poly(dimethylsiloxane) (PDMS) mem-
branes as the most popular separation barrier used in recovery
of alcohols from water. PDMS is an elastomeric material which can
be utilized for fabrication of hollow fibers, unsupported sheets and
thin layer supported membranes. Separation factor for PDMS
membranes in water–ethanol pervaporation is in the range of
4.4 to 10.8. Such broad range is a result of performance parameters
for a given polymer and separation conditions. Reported separa-
tion factors of butanol recovery from n-butanol–water mixture for
poly(dimethylsiloxane) also cover a fairly broad range, from 20 to
60, which is much wider than that of ethanol–water system
[42,43].
Several PDMS membranes modified with octadecyldiethoxy-
methylsilane (M1) and poly(dimethylsiloxane) integrated with
PTFE (M2) or PP (M3) support have been tested by Vane [42].
Selectivity coefficients for M1–M3 membranes were equal to 16.3,
14.0 and 12.6, respectively, in water–ethanol separation [42].
Other polymeric membranes have been also tested by pervapora-
tion for selective recovery of ABE fermentation products or model
solutions. Application of these membranes will be described more
in detail in this section. To compare apparent properties of various
membranes, separation factor (β) defined by Eq. (1) is used [96]:
β ¼
Ai=Aj
Bi=Bj
ð1Þ
where Ai, Aj are molar or weight fractions of component i and
component j in permeate, respectively. Bi and Bj are molar or
weight fractions of components in feed.
Rozicka et al. [43] tested properties of PDMS based commercial
membranes (Pervatech, Pervap 4060 and PolyAn) in contact with
binary aqueous mixtures of acetone, n-butanol and ethanol at
25 1C. Authors obtained the best n-butanol recovery from water-n-
butanol mixture during vacuum pervaporation with Pervap 4060
membrane. In this work apparent and intrinsic membrane proper-
ties were discussed in detail. It was shown that membranes
are selective towards organic compounds; however, considering
intrinsic membranes properties it was found that all tested PDMS
membranes transport n-butanol the most selectively among all
organic solvents used in this study [43].
Niemisto et al. [44] investigated properties of composite PDMS
on polyacrylonitrile support membrane (Pervatech) for recovery of
acetone, n-butanol and ethanol from binary, ternary and quatern-
ary model aqueous solutions at 42 1C. At 3.5 wt% of n-butanol in
feed separation factor was equal to 22 during PV experiments
performed for n-butanol-water mixture, whereas at 3.23 wt%
BuOH content in acetone–butanol–ethanol–water mixture,
separation factor was also equal to 22. It was also pointed out
that organic compounds and water fluxes do not change signifi-
cantly comparing binary, ternary or quaternary mixtures [44].
Kujawski et al. [97] tested properties of PDMS based mem-
branes (Pervap 1070 and Pervatech) in recovery of acetone,
butanol and ethanol from binary and quaternary aqueous mix-
tures by pervaporation. Separation factor for butanol removal
from its binary aqueous mixture at 1 wt% of organic component
in feed was equal to 27 and 40 for Pervap 1070 and Pervatech
membranes, respectively. Membrane with the best pervaporative
efficiency during VPV with binary water–butanol mixture (Per-
vatech) was chosen for next pervaporation measurements with
quaternary aqueous mixtures at 65 1C. Separation factor of
organics recovery from quaternary mixture was equal to 24.5,
27.6 and 8.5 for acetone, butanol and ethanol, respectively. The
authors [97] performed also a simulation of batch pervaporation
process. It was found that the needed to recover a given amount
of organics is dependent on the feed volume to membrane area
ratio. Moreover, it was claimed that longer duration of batch
pervaporation process results in a more diluted permeate,
what was explained by the decrease of organic components
fluxes with the duration of batch pervaporation whereas water
flux is practically constant.
Liu et al. [45] tested properties of in situ crosslinked poly-
dimethylsiloxane/brominated polyphenylene oxide (c-PDMS/
BPPO) membrane for n-butanol recovery by pervaporation. During
PV experiments with PDMS/BPPO membrane in contact with n-
butanol–water mixture total flux of 220 g m 2
h 1
and separation
factor of 35 were obtained.
Fouad and Feng [46] tested separation properties of a silicalite-
filled PDMS (Pervap 1070) composite membrane adapted to
remove n-butanol from dilute aqueous solutions containing n-
butanol up to 0.5 wt% by vacuum pervaporation. Authors found
out that water flux increased linearly with n-butanol content in
feed. In the same experiment it was also shown that silicate fillers
exhibit strong affinity to n-butanol particles because of increasing
n-butanol flux. At 0.3 wt% of n-butanol in feed and 25 1C feed
temperature BuOH flux of around 5 g m 2
h 1
and separation
factor (β) of ca. 18 were obtained, whereas at 65 1C n-butanol flux
was equal to around 16 and β was equal to ca. 10.
Li et al. [47] tested properties of tri-layer PDMS composite
membrane in contact with n-butanol by pervaporation. The tested
membrane consisted of PDMS active layer and dual support layers
of high porosity polyethylene (PE) and high mechanical stiffness
perforated metal (PDMS/PE/Brass). With the feed solution of 2 wt%
n-butanol in water at 37 1C, the PDMS/PE/Brass support composite
membrane confers a total flux of 132 g h 1
m 2
and a separation
factor of 32. It was also shown that the increase of the PDMS layer
thickness results in improvement of separation factor values and
decline of the total flux [47].
García et al. [48] tested efficiency of n-butanol recovery from its
water salt solution by pervaporation. During VPV experiments the
following commercially available membranes were applied: mem-
brane with a selective layer composed of polysiloxane polymer
(CELFA) and PERTHESE membrane of selective layer consisting of
silicone elastomer with dimethyl and methyl vinyl siloxane copo-
lymers. At tested concentration range (0–1.36 wt%) and at 40 1C
separation factors of n-butanol recovery equal to ca. 56 and 39
were obtained for CELFA and PERTHESE membrane, respectively.
Total fluxes obtained at 40 1C for PERTHESE and CELFA membranes
were equal to 34 g m 2
h 1
and 366 g m 2
h 1
, respectively.
Liu et al. [41] found out that selectivity of poly(ether block
amide) (PEBA2533) membrane during pervaporation in contact
with water–ABE systems at 23 1C follows the order of n-butano-
l4acetone4ethanol. At 5 wt% of organic compound content in

feed fluxes obtained for n-butanol, acetone and ethanol, were
equal to 42.2 g m 2
h 1
, 21.4 g m 2
h 1
and 13.1 g m 2
h 1
,
respectively. Separation factor was equal to 5.9, 3.3 and 2.5 for
n-butanol, acetone and ethanol, respectively [41].
Tan et al. [49] tested n-butanol recovery by pervaporation in
contact with composite membranes. The membranes were pre-
pared by incorporation of ZSM-5 zeolite into poly(ether-block-
amide) (PEBA). The effect of various content of zeolite in PEBA on
pervaporation performance was tested. Inclusion of ZSM-5 zeolite
results in decrease of the activation energy of n-butanol flux
through the composite membrane. The authors [49] tested proper-
ties of PEBA membranes filled with 2 wt%, 5 wt% and 10 wt% of
ZSM-5 in their structure. The best transport and selective proper-
ties were obtained for the membrane with 5% addition of zeolite
filler to the membrane. In the work of Tan et al. [49] investigation
of membrane performances at various temperatures was also
presented. Obviously it was found that the highest fluxes were
obtained at the highest temperature tested (45 1C in this work).
Vrana et al. [50] used polytetrafluoroethylene flat sheet mem-
branes to be used in pervaporation in contact with model n-
butanol–water mixture and with model solutions of ABE products.
Authors tested influence of feed temperature (in the range of 30–
55 1C) on pervaporation process performance in contact with
binary and quaternary mixtures, finding that fluxes increase with
the increase of feed temperature during experiments with n-
butanol–water and ABE–water mixtures. Separation factor (β)
obtained during PV with ABE–water solution also increased at
higher feed temperature in whole tested temperature range,
whereas the highest β value was reached during PV experiments
at 45 1C (β¼12.9) in contact with binary mixture and at 50 1C and
55 1C separation factor was equal to 9.9 and 5.2, respectively. It has
been also pointed out that in contact with n-butanol–water
system lower separation factors were obtained than in contact
with ABE–water system, which was attributed to the fact that the
presence of the ABE mixture enhances the flux and selectivity of
the PTFE membranes [50].
Claes et al. [51] investigated properties of laboratory made silica-
supported poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes
filled with silica in contact with binary aqueous mixtures of ethanol
and n-butanol. The highest performance of vacuum pervaporation
process was reached for PTMSP membrane containing 25 wt% of
silica in its structure. During VPV experiments with 25 wt% silica
filled PTMSP membrane in contact with ethanol–water (5 wt% of
EtOH in feed) mixture, 9500 g m 2
h 1
flux and separation factor of
18.3 were obtained. Whereas during VPV measurements in contact
with n-butanol–water (5 wt% of BuOH in feed) system, flux of
9500 g m 2
h 1
and separation factor of 104 were found.
Tong et al. [52] tested properties of hydroxyterminated
polybutadiene-based polyurethaneurea (HTPB-PU) by pervaporation
in contact with dilute aqueous solutions of acetone and n-butanol. The
increase of n-butanol separation factor value with increasing feed
concentration was observed, however the reverse tendency was
obtained for acetone. Authors [52] pointed out that the separation
efficiency of the ternary mixture was better than that of the binary
mixture at the same organic component content in feed. Such a
phenomenon was attributed to the permeant–permeant and per-
meant–membrane interactions. The pervaporation performance for
the fermentation broth was better comparing with the model solu-
tions (ternary system) at similar feed composition [52].
Wei et al. [98] tested influence of PDMS chains length on the
performance of PDMS/ceramic composite membranes for perva-
porative recovery of ethanol from its aqueous solutions. The
PDMS/ceramic composite membrane prepared using PDMS of
the highest molecular weight possesses superior performance
than membrane fabricated using poly(dimethylsiloxane) of lower
molecular weight. The total flux and the separation factor of a
PDMS/ceramic (PDMS layer of 5 mm) composite membrane were
1600 g m 2
h 1
and 8.9, respectively, during VPV experiments
performed at 40 1C feed temperature and 5 wt% of ethanol content
in the feed solution [98].
Fadeev et al. [99] tested properties of PTMSP membranes
during butanol recovery from aqueous solutions and ABE fermen-
tation broth. Influence of feed temperature on VPV process
performance was tested. The highest selectivity of PTMSP mem-
brane in butanol recovery was obtained at feed temperature equal
to 37 1C (β¼135). In a subsequent paper, Fadeev et al. [100] tested
also effectiveness of butanol recovery from diluted aqueous solu-
tions by vacuum pervaporation. The authors [100] observed
decline of flux through PTMSP membrane with duration of VPV
experiments what was attributed to compaction of the membrane
structure [100]. In another work Fadeev et al. [101] tested proper-
ties of PTMSP based membrane during pervaporative recovery of
ethanol from model aqueous solutions and yeast fermentation
broth. During VPV experiments performed in contact with model
ethanol–water mixture separation factor of 9 and total permeate
flux equal to ca. 320 g m 2
h 1
were obtained. Deterioration of
PTMSP membrane performance in the presence of yeast fermenta-
tion broth was observed [99,101]. Borisov et al. [102] tested
properties of poly[1-(trimethylsilyl)-1-propyne] membrane filled
with poly(dimethylsilmethylene) (PDMSM) in pervaporative
recovery of butanol. PTMSP/PDMSM modified membranes demon-
strated better butanol/water pervaporation selectivity and perme-
ability than native PTMSP membranes. Authors [102] claimed that
introduction of 1.2 wt% of PDMSM into poly[1-(trimethylsilyl)-1-
propyne] membrane structure results in increasing permeate flux
up to 75% and separation factor to 67% comparing with native
PTMSP membranes. Improved pervaporative properties of PTMSP/
PDMSM modified membranes in butanol recovery were attributed
to higher hydrophobicity of filled membranes [102].
Dubreuil et al. [103] utilized PTMSP membranes during perva-
porative recovery of n-butanol directly from fermentation broth.
Drop of permeate flux through PTMSP membrane during VPV
process was obtained due to occurrence of significant membrane
fouling by fermentation process intermediates. In order to dimin-
ish negative impact of fermentation bioproducts on pervaporation
process performance, the upstream nanofiltration was applied. It
was shown that the pretreatment of the fermentation mixture
resulted in the improvement of separation factor by the factor
4 and increase of total permeate flux from 90 g m 2
h 1
(without
pretreatment) to 370 g m 2
h 1
(with nanofiltration).
Xue et al. [104] tested properties of PDMS–PVDF composite
membranes in recovery of butanol from aqueous model mixtures
and fermentation broth. Authors [104] observed a minor diminution
of butanol separation factor during recovery of the component from
quaternary aqueous mixture comparing with results performed with
binary water–butanol mixture. It was attributed to preferential
dissolution and competitive permeation of acetone and ethanol
through the membrane. During pervaporation experiments with
fermentation broth, butanol content in permeate and flux of the
organic component maintained at a steady level within the range of
139.9–154.0 g L 1
and 13.3–16.3 g m 2
h 1
, respectively.
Kujawa et al. [105] tested properties of surface hydrophobized
alumina and titania ceramic membranes during pervaporation of
water–butanol mixture. Membranes surfaces were modified by
grafting with 1H,1H,2H,2H-perfluorooctyltriethoxysilane and due
to this membrane properties were changed from hydrophilic to
hydrophobic. Modified membranes selectively transported buta-
nol from its aqueous mixture (separation factor equal to 2).
Concise summary of various membranes and conditions dis-
cussed above along with the pervaporation performances is
presented in Table 3.
656

Total flux (Jt) and separation factor (β) can be combined into the
so called Pervaporation Separation Index (PSI), according to Eq. (2).
PSI ¼ Jt β 1

ð2Þ
Isopsines i.e. lines corresponding to constant values of PSI, were
used to compare various membranes efficiency in butanol recovery
from its model aqueous solutions. In Fig. 2 dashed and solid lines
correspond to PSI equal to 10 kg m 2
h 1
and 20 kg m 2
h 1
,
respectively. Membranes of the best performance in butanol recovery
were PDMS and ZSM-5 zeolite-filled PEBA. Process separation index
in between 10 and 20 kg m 2
h 1
was obtained for two PDMS
membranes, PDMS filled by hydrophobic zeolite and PTMSP/PDMSM
membrane. It has to be pointed out that the PTMSP/PDMSM
membrane possess the highest separation factor value; however,
flux through the membrane is not impressive. Most of membranes
presented in Fig. 2 possess PSI value lower than 10 kg m 2
h 1
.
Efficiency of ABE recovery by pervaporation process can by
reduced by fouling. The fouling is described as adsorption of
macromolecules on the surface and inside the membrane [99,107].
The mentioned phenomenon results in reduction of flux and due to
this caused drop in membrane performance [99]. To reduce negative
impact of the fouling macromolecules should be removed from the
feed before pervaporation or membrane cleaning procedure should
Table 3
Comparison of various hydrophobic membranes performance in pervaporative recovery of acetone, n-butanol and ethanol.
Membrane Organic solvent content in feed [wt%] T [1C] Organic flux [g m 2
h 1
] Separation factor [–] Ref.
Binary model mixtures
Acetone–water
HTPB-PU ca. 0.5 40 ca. 1 ca. 14 [52]
PDMS (Pervatech) 2 25 344 29 [43]
PDMS (Pervap 4060) 2 25 431 66 [43]
PDMS (PolyAn) 2 25 649 40 [43]
n-Butanol–water
ZSM-5 zeolite-filled PEBA (5% of zeolite) 4.3 35 719.3 33.3 [49]
ZSM-5 zeolite-filled PEBA (5% of zeolite) 2.5 45 569 30.7 [49]
25 wt% silica filled PTMSP 5 50 9500 104 [51]
PDMS/PE/Brass 2 37 132 (total flux) 32 [47]
c-PDMS/BPPO 5 40 220 (total flux) 35 [45]
PTFE 1.25 (v./v.) 40 170 (total flux) 8.5 [50]
HTPB-PU ca. 1 40 ca. 2 ca. 11 [52]
Silicalite-filled PDMS 0.3 25 ca. 5 ca. 18 [46]
Silicalite-filled PDMS 0.3 65 ca. 16 ca. 10 [46]
PDMS (Pervatech) 2 25 112 10 [43]
PDMS (Pervap 4060) 2 25 224 36 [43]
PDMS (PolyAn) 2 25 202 11 [43]
PDMS (Pervatech) 3.5 42 ca. 950 22 [44]
Hydrophobic zeolite filled PDMS (Pervap 1070) 1 65 ca. 100 40 [97]
PDMS (Pervatech) 1 65 ca. 750 27 [97]
PTMSP/PDMSM 2 25 120 128 [102]
PTMSP 2 37 ca. 800 (total flux) 135 [99]
PTMSP 1 25 20 52 [100]
PTMSP 1 70 413 70 [100]
PDMS–PVDF 1.5 (initial concentration) 37 31.5 17 [104]
Surface modified ceramic 1 35 ca. 50 2 [105]
Ethanol–water
25 wt% silica filled PTMSP 5 50 9500 18.3 [51]
PTMSP 6 30 320 (total flux) 9 [101]
PDMS/ceramic composite membrane 5 40 1600 (total flux) 8.9 [98]
PDMS (Pervatech) 2 25 75 7 [43]
PDMS (Pervap 4060) 2 25 61 10 [43]
PDMS (PolyAn) 2 25 152 7 [43]
Ternary model mixtures
Acetone-n-butanol–water
HTPB-PU ca. 0.5 (AcO) 40 ca. 1.5 (AcO) ca. 15 (AcO) [52]
ca. 1 (BuOH) ca. 2 (BuOH) ca. 12 (BuOH)
Quaternary model mixtures
PTFE 1.25 (v./v.) 40 980 (total flux) 9.5 [50]
PDMS (Pervatech) 1.54 (AcO) 42 ca. 480 (AcO) 22 (AcO) [44]
3.23 (BuOH) ca. 800 (BuOH) 22 (BuOH)
0.43 (EtOH) ca. 80 (EtOH) 6 (EtOH)
Pervatech (PDMS) 1.60 (total organics in feed, ratio 3:6:1) 65 ca. 350 (AcO) 24.5 (AcO) [97]
ca. 750 (BuOH) 27.6 (BuOH)
ca. 50 (EtOH) 8.5 (EtOH)
PDMS–PVDF 0.75 (AcO) 37 18 (AcO) 15 (AcO) [104]
1.5 (BuOH) 32 (BuOH) 14 (BuOH)
0.25 (EtOH) 1 (EtOH) 3 (EtOH)
Fermentation broth
HTPB-PU 0.5 (AcO) 0.5 (AcO) 15.3 (AcO) [52]
1.1 (BuOH) 1.1 (BuOH) 13.7 (BuOH)
PTMSP – 37 90 (total flux) 24 (BuOH) [103]
PDMS–PVDF – 37 8 (AcO) 23 (AcO) [104]
20 (BuOH) 14 (BuOH)
0.5 (EtOH) 5 (EtOH)
Silicone 6.0 (ABE) – 16 (ABE) 25 (ABE) [106]

be applied [99,108]. Membranes after rinsing could restore its
previous properties [108].
2.2. Integration of n-butanol fermentation with various removal
techniques
Müller and Pons [109] tested properties of microporous (PTFE,
PP) and nonporous (silicone) membranes in pervaporation
coupled to alcoholic fermentation. Such solution allowed to obtain
improved productivity of ABE fermentation products. In terms of
long time operation process, microporous membranes can
undergo clogging of the pores, which would result in reduction
of porous membrane properties. During pervaporation experi-
ments gradual loss of the hydrophobicity of the polypropylene
membrane was observed, whereas silicone material does not
suffer from this problem [109].
Mulder et al. [110] proposed multistage set-up to be used for
continuous removal of ethanol from fermentation broth. The rig
consisted of fermenter directly coupled with ultrafiltration (UF)
mode. Permeate of 5 to 10 wt% ethanol content from UF was
directly transported to VPV rig, where permeate of around 40 wt%
was obtained. The permeate was transmitted to the second VPV
mode, in which product liquid of 95 wt% was obtained. Unfortu-
nately, no practical application of proposed solution was
described. Authors [110] investigated properties of cellulose acet-
ate (CA), polysulfone (PSf) and poly(dimethylphenyleneoxide)
(PPO) membranes by vacuum pervaporation in contact with
water–ethanol (50 wt% of organic compound in feed) system at
20 1C. Separation factor towards water equal to 12.3, 3.0 and
9.3 for CA, PSf and PPO membranes, respectively, was obtained.
Vane and Alvarez [111] described the separation of n-butanol–
water and ABE–water solutions using a combination of unit
operations such as: vapour stripping, vapour compression, and
vapour permeation membrane separation. Such procedure was
termed the membrane assisted vapour stripping (MAVS). In the
MAVS process volatile compounds are removed from the broth in a
stripping column and subsequently the vapours are adiabatically
compressed. Such procedure allows raising the pressure of the
stream and maintains it in the vapour phase. In a subsequent step
the compressed vapour stream is separated into solvent- and
water–rich vapour streams with a vapour permeation membrane
unit. The water–rich vapour stream of permeate from the
membrane is returned to the stripping column to diminish the
reboiler heat requirement [111].
Qureshi et al. [106] described production of ABE from concen-
trated whey/lactose solutions and removal of acetone, butanol,
and ethanol by pervaporation technique. The whey/lactose as a
fermentation substrate was chosen due to the fact that it requires
less upstream processing than other substrates for ABE fermenta-
tion and it is commercial dairy industry by-product. 211 g L 1
of
lactose was used to obtain total ABE productivity of 0.43 g L 1
h 1
and total amount of ABE in the reactor of 79.0 g (acetone 4.8 g,
butanol 72.4 g, and ethanol 1.8 g). Silicone membrane was applied
during pervaporative recovery of fermentation products. ABE
separation factor was equal to ca. 25 and total ABE flux was ca.
16 g m 2
h 1
at 6 wt% of total organics in feed. It was concluded
that pervaporation allowed to selectively recover ABE fermenta-
tion products and it minimized diffusion of water through the
membrane and due to this significantly less energy is necessary for
product recovery comparing with gas stripping [106].
Xue et al. [112] applied two-stage gas stripping method to
perform recovery of butanol directly from ABE fermentation broth
in a fibrous bed bioreactor. The first-stage of gas stripping was
coupled directly with fermentation broth. The aim of first stage
was to mitigate inhibition of the ABE fermentation products
towards bacteria cells, whereas the second stage gas stripping
allowed for further concentration of solvents. Influence of several
parameters (butanol concentration, temperature of feed, gas flow
rate, cooling temperature) on stripping gas process efficiency was
tested. The optimal conditions chosen for two-stage process given
in that study were 37 1C of fermentation broth in the first stage,
55 1C feed temperature for the second stage and gas flow rate
equal to 1.6 L min 1
. After two-stage gas stripping process, the
composition of the final product was equal to 515.3 g L 1
,
139.2 g L 1
and 16.6 g L 1
of butanol, acetone, and ethanol,
respectively. It was claimed that such a method allows to reduce
total energy consumption of the butanol recovery process [112].
Chen et al. [113] investigated butanol recovery using intermit-
tent permeating–heating–gas stripping method integrated with
ABE fed-batch fermentation. During solvents recovery, performed
at 70 1C, 290 g L 1
of glucose was utilized, 106.27 g L 1
of ABE and
66.09 g L 1
of butanol were produced. During the removal process
a highly concentrated condensate containing ca. 15% (w/v) buta-
nol, 4% (w/v) acetone, and o1% (w/v) ethanol was received, due to
Fig. 2. Comparison of various membranes performance in n-butanol recovery by VPV; solid isopsine line corresponds to PSI equal to 20 kg m 2
h 1
and dashed isopsine line
to PSI equal to 10 kg m 2
h 1
.
658

this highly concentrated butanol solution (ca. 70% (w/v)) was
obtained after phase separation. The authors [113] concluded that
the integrated fermentation process with periodic nutrient sup-
plementation allowed to maintain a stable productivity and high
butanol yield for an extended period of time.
3. Final remarks
Development of efficient approach for butanol production is a
very fast developing area. One of promising approaches is butanol
production and recovery from renewable resources. However, a lot
of variables have to be taken into account to determine profit-
ability of butanol production. Qureshi and Manderson [114]
performed cost analysis of renewable resources bioconversion
into ethanol. Recovery of ethanol by pervaporation was examined
and costs of VPV process were compared with those for distillation
method. The authors [114] found that application of membrane
recovery to a production plant of capacity 58.6 106 L year 1
of
ethanol that utilizes a continuous wood hydrolysate fermentation
process allow to reduce cost of ethanol production from $0.52/L
(distillative recovery) to $0.46/L (membrane recovery). An increase
of membrane flux by a factor of 5 allows reducing this price to
$0.42/L. Membrane prices has significant impact on ethanol
production costs; however, application of larger plants allows to
obtain only slightly lower ethanol prices ($0.40/L).
One can assume that similar solutions applied to n-butanol recov-
ery, including shift from distillation towards more energy-efficient
methods will decrease n-butanol production price, making it even
more attractive and economically competitive as a biofuel.
There is a need for cheaper feedstocks, improved ABE fermen-
tation process performance and more sustainable operation meth-
ods for solvents recovery [58]. Especially that the price of
feedstock contribute up to 79% of ABE solvents production costs
and additionally, the feedstock price depends strongly on market
prices fluctuations [58]. This renders the need for the possibility of
converting plants to use cheaper fermentation feedstocks [58].
There are negative and positive aspects of integrated n-butanol
fermentation set-up with separation techniques [115]. Practical
application of a combined system will be possible if the integrated
process is microbial friendly, scalable, non-foulable, and enhances
n-butanol productivity. Application of the various separation
techniques like adsorption, gas stripping, liquid–liquid extraction,
perstraction and pervaporation diminishes n-butanol toxicity
towards fermentation broth and allows to obtain increased pro-
ductivity. Among all mentioned techniques only gas stripping has
increased yield of the combined process. There are also limitations
of n-butanol recovery methods when combined with fermentation
[115]. Application of adsorption causes loss of nutrients to adsor-
bent, clogging, and loss of fermentation intermediate products.
Gas stripping technique is limited by a low n-butanol stripping
rate, whereas during liquid–liquid extraction not only the extrac-
tant used can be toxic to cells, but also formation of precipitate
layer, emulsion and loss of fermentation intermediate products
can occur. During pertraction process loss of intermediate fermen-
tation products to extractant phase and membrane fouling can
take place. Application of pervaporation can cause losses of
fermentation intermediate products. Moreover, the membrane
fouling is also possible [115].
Recovery techniques allow efficient removal of ABE fermenta-
tion products, although industrial applications of the techniques
are still not so popular. More effort should be paid to commercia-
lise recovery techniques in industrial applications.
Acknowledgements
This work was financially supported by the Grant number N
N209 761240 founded by Polish Ministry of Science and Higher
Education.
Authors would like to kindly thank Dr. Maciej Kujawski for his
help with the text editing.
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