1. Study on Preparation of Difunctional Hollow Fiber Composite Membrane with Catalysis and
Pervaporation Capabilities and Process of Reactive Distillation
Pervaporation membrane is the core of pervaporation process, the chemical property and physical
structure of which determine the pervaporation separation efficiency to a great extent.
Difunctional membrane coupling catalysis with pervaporation has good catalytic performance and
even better separation performance over pervaporation membrane. Only a simple repetition of the
methods of preparation pervaporation membrane is hard to prepare catalytic membrane with good
performance. It must combine both preparation methods of membrane and catalyst together to
make innovation. In this paper, perfluorosulfonic acid (PFSA) was used as catalyst to prepare
difunctional hollow fiber composite membranes with two layers, catalyst layer and separation
layer, by dip-coating method. The difunctional hollow fiber composite membranes with
remarkable capabilities were chosen and used as packing in distillation, and the operation
conditions of reactive distillation produce ethyl acetate were optimized when using difunctional
hollow fiber as packing and catalyst. The conclusions were as follows:Firstly, three kinds of
single-function pervaporation plate composite membranes, chitosan-sodium
alginate/polyacrylonitrile (CS-SA/PAN), chitosan-sodium tripolyphosphate/polyacrylonitrile
(CS-STPP/PAN) and glutaraldehyde-poly(vinyl alcohol)/polyacrylonitrile (GA-PVA/PAN), were
prepared by dip-coating method using PAN ultra filtration membranes as support membranes, and
were characterized by FTIR, SEM, EDX, swelling and dehydration ethyl acetate/water solution
through pervaporation process. The results showed that the permeation fluxes of them were 348
g/(m2·h),340 g/(m2·h) and 168 g/(m2·h), and the corresponding separation factors were
7245,6268 and 9182, respectively, when dehydrating 97wt.% ethyl acetate aqueous solution at 40
℃. The swelling degree, which represented the stabilization of membrane, could reach 51.0%,
37.4% and 23.7% in 97wt.% ethyl acetate aqueous solution, respectively. Considering the
stabilization of membrane and the acetic acid-ethanol esterification reaction, GA-PVA/PAN
single-function pervaporation plate composite membrane was chosen for further study since CS
could dissolve in dilute acetic acid solution.Secondly, a surface-crosslinking reaction model was
established to predict the impact of crosslinking agent concentration and surface-crosslinking
reaction time on the morphology and the structure of membrane, and CS-STPP/PAN
single-function pervaporation plate composite membrane was used to verify this model. The
results showed that the surface-crosslinking reaction between CS and STPP on CS-STPP/PAN
single-function pervaporation plate composite membrane reached the equilibrium state when
reacted 15 min, agreeing well with the corresponding report of literature. The crosslinking ratio
had an exponential relationship with surface-crosslinking reaction time and a linear relationship
with crosslinking agent concentration. The expected ideal pervaporation composite membrane
could be prepared through controlling crosslinking agent concentration and surface-crosslinking
reaction time.Then, GA-PVA/PAN single-function pervaporation plate composite membrane was
prepared as single-function pervaporation hollow fiber composite membrane and their capabilities
were characterized. The results showed that 4 wt.% GA surface crosslinked PVA/PAN hollow
fiber composite membrane had good capabilities with permeation flux 181 g/(m2 h), the
corresponding separation factors of water to ethanol 203 and water to ethyl acetate 3953 when
dehydrating top coarse ester (ethyl acetate 87.36wt.%, ethanol 3.73wt.% and water 8.91 wt.%)
through pervaporation process. And then three series (nano SiO2, nano TiO2 or nano Al2O3),27

2. kinds of difunctional hollow fiber composite membranes with catalysis and pervaporation
capabilities were prepared by dip-coating catalytic solution on 4 wt.% GA surface crosslinked
PVA/PAN single-function hollow fiber composite membrane. The catalytic solution consisted of
PFSA (used as catalyst), PVA (used as adhesion), and nano SiO2, nano TiO2 or nano Al2O3 (used
as support). Their structures and performances were characterized through the water contact angle,
mechanical strength, FTIR, SEM, EDX, XRD, TGA, dehydrating top coarse ester by
pervaporation process and acetic acid-ethanol esterification reaction. The results showed that
PFSA was successfully coated and adhered well by PVA on the outer surface of difunctional
hollow fiber composite membrane, and nano SiO2, nano TiO2 or nano Al2O3 supplied a large
amount of specific surface area for PFSA. The difunctional hollow fiber composite membranes
had good hydrophilic and mechanical properties, and had remarkable separation performance and
catalytic activity when the catalytic solution consisted of 2wt.% PFSA, 3wt.% PVA, and 8wt.%
nano SiO2, nano TiO2 or nano Al2O3 (named as DMS1, DMT1 and DMA1, respectively). The
permeation flux could reach 179 g/(m2 h), the corresponding separation factor of water to ethanol
was 95 with no ethyl acetate permeating. Comparing with blank, the acetic acid-ethanol
esterificatoin reaction time was shortened greatly when added difunctional hollow fiber composite
membrane in the reaction feed solution as catalyst. The conversion at the reaction time 100min
could reach that of 400min in blank, as high as 40.0%(the equilibrium conversion is 66.7%, total
reflux). The FTIR and SEM had little change when acetic acid-ethanol esterification of 24h,
indicating that the difunctional hollow fiber composite membrane had good stabilization. DMS1,
DMT1 and DMA1 were chose for further study.Consequently, the optimized DMS1, DMT1 and
DMA1 three kinds of difunctional hollow fiber composite membranes were used as structured
packings in distillation. Both of vapor and liquid flowed on the shell side of the difunctional
hollow fiber composite membranes. The distillation capabilities were characterized by
isopropanol-water and ethanol-water systems. The results showed that, comparing with traditional
structured packing, difunctional hollow fiber composite membrane structured packing could be
operated successfully above the flooding limits and significantly reduced the height of transfer
unit (HTU); ant it had the similar performances (despite both of vapor and liquid flowed on the
shell side of the membrane) with the hollow fiber distillation reported in literatures (both liquid
and vapor had their own channels). The HTU was only 9.0 cm for isopropanol-water system and
3.6 cm for ethanol-water system, representing higher separation efficiency. The results showed
that it was feasible to use difunctional hollow fiber composite membrane as packing, and thus
provided experiment basis for reactive distillation and pervaporation coupling process.Finally, the
operation conditions of reactive distillation produce ethyl acetate were optimized using
difunctional hollow fiber composite membrane as packing and catalyst as above. The results
showed that the difunctional hollow fiber as distillation packing ensured good distillation
characteristics, meanwhile, a large contact area between catalytic film and reaction mixture,
combined with the short diffusion length, ensured a high overall efficiency and selectivity of the
reaction. The optimal operating conditions were mole ratio of acetic acid to ethanol of 4, reboiler
oil temperature of 145℃, fiber numbers of 40, reflux ratio of 2 and fiber types of nano TiO2
embedded difunctional hollow fiber membrane (named as DMT1). Meanwhile, the conversion of
esterification could reach 97.3%, and the yield of ethyl acetate could reach 86.8%.
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