Effective recovery of acetic acid from wood vinegar by reactive distillation using tungstophosphoric acid-active carbon catalyst

Article abstract of DOI:10.14233/ajchem.2014.16627

The recovery of acetic acid from wood vinegar by reactive distillation using tungstophosphoric acid-active carbon as catalyst has been studied. Methyl acetate is obtained as esterification product at the top of column. The loading capacity of tungstophosphoric acid on active carbon was optimized using batch distillation. In addition, the influence of various factors such as feed flow rate, MeOH vapor rate, rectifying section height and reflux ratio, on the conversion rate of acetic acid were investigated by using a model solution. A 71.94% recovery of acetic acid is obtained from wood vinegar under the following optimal conditions: loading capacity 33%, feed flow rate 60 g/h, MeOH vapor rate 114 g/h, rectifying section height 250 mm and reflux ratio 9:1.

Full text of DOI:10.14233/ajchem.2014.16627

Asian Journal of Chemistry; Vol. 26, No. 21 (2014), 7311-7314
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16627
Effective Recovery of Acetic Acid from Wood Vinegar by Reactive
Distillation using Tungstophosphoric Acid-Active Carbon Catalyst
1,2
1
1
1
2
2,*
SHUANGMING LI , XUEJIAO YANG , JIAXIANG CHEN , XIUJUAN WANG , WENXIU LI and SANSAN YU
1College of Chemical Engineering, Shenyang University of Chemical Technology, Shenyang 110142, P.R. China
2Key Laboratory of Chemical Separation Technology of Liaoning Province, Shenyang University of Chemical Technology, Shenyang 110142,
P.R. China
*Corresponding author: Tel./Fax: +86 24 89383730; E-mail: yu.sansan@gmail.com
Received: 4 November 2013;
Accepted: 19 March 2014;
Published online: 30 September 2014;
AJC-16126
The recovery of acetic acid from wood vinegar by reactive distillation using tungstophosphoric acid-active carbon as catalyst has been
studied. Methyl acetate is obtained as esterification product at the top of column. The loading capacity of tungstophosphoric acid on
active carbon was optimized using batch distillation. In addition, the influence of various factors such as feed flow rate, MeOH vapor rate,
rectifying section height and reflux ratio, on the conversion rate of acetic acid were investigated by using a model solution. A 71.94 %
recovery of acetic acid is obtained from wood vinegar under the following optimal conditions: loading capacity 33 %, feed flow rate 60
g/h, MeOH vapor rate 114 g/h, rectifying section height 250 mm and reflux ratio 9:1.
Keywords: Reactive distillation, Acetic Acid, Wood vinegar, Tungstophosphoric acid, Recovery
limitations, improved selectivity and increased process effi-
ciency. In addition, a reactive distillation method can also
reduce the costs of investments and operations obviously. It
has been reported by some researchers that reactive distillation
can be used for recovery of organic acid from aqueous solu-
tions10-14. In these processes, catalysts play the important role
and affect the efficiency and the cost directly. Ion exchange
resins and zeolite were the catalysts used commonly to deal
INTRODUCTION
Wood vinegar, a kind of brownish-black liquid, is gene-
rated in the process of charcoal production. The major consti-
tuent of wood vinegar is water, which makes up as much as
90 %. In addition to water, more than 200 organic compounds
are included in smaller quantities, such as acetic acid,
formaldehyde, acetone, methanol, tar and so on1, 2. In many
cases, acetic acid makes up about 90 % of total organic consti-
tuents. A large number of wood vinegar is being produced
and discarded every day from the charcoal plant, which causes
serious waste of acetic acid and environmental pollution.
Therefore, it is very important and urgent to recover acetic
acid from the acidic water.
with 5-30 % acidic acid solutions13-16
.
Heteropolyacids, a kind of polynuclear complexes con-
taining an oxygen bridge, are frequently used as a re-usable
acid catalyst in many chemical reactions17,18. In addition of
strong acidic ability, heteropolyacids also possess of stable
structure and good heat resistance, which was more applicable
to industrial process. Therefore, the aim of this investigation
was to recover acidic acid from wood vinegar to synthesize
methyl acetate by using reactive distillation with tungstophos-
phoric acid as catalyst.
It is difficult to separate acidic acid from water due to the
miscibility between acidic acid and water. So far, some sepa-
ration methods are applied to recovery diluted acid from indus-
trial or medicine waste water, including ordinary distillation,
azeotropic distillation, extractive distillation, solvent extraction
and complexation extraction3-9. However, there are many
disadvantages, such as low extraction yield, high cost and use
of toxic organic solvents, limiting their application in industrial
process.
EXPERIMENTAL
Wood vinegar, containing approximately 10 % acidic acid,
was obtained from wood processing plants (Fushun, Liaoning,
China). CH3COOH, HCl and CH3OH of analytical grade,
H3O40PW12·XH2O and activated carbon (20-40 mesh) were
purchased from Guoyao Group Chemical Reagent Shenyang
Co., Ltd. and distilled water was used in all experiments.
Reactive distillation (RD), an effective separation method,
combines the chemical reaction and the distillative separation
of the product mixture in a single column. It is receiving incre-
asing attention due to the elimination of chemical equilibrium

7312 Li et al.
Asian J. Chem.
100
90
80
70
60
50
10 % acidic acid aqueous solution was prepared firstly as
a simplified model solution, which was used as the feedstock
in the following optimization process.
GC analysis: GC analysis of the products of reactive
distillation was carried out on a GC7900 gas chromatograph
(Shanghai Techcomp Bio-equipment Ltd., China) with a
Porapak Q packed column (3 mm × 2 m) equipped with a
TCD detector. GC was operated with the auto injection of 0.4
µL. Both the injector and the detector temperatures were
150 °C. The oven temperature was 120 °C for 11 min and
then increased to 180 °C at a rate of 25 °C/min. The retention
times of all the individual compounds were verified using
authentic samples.Area correction normalization method was
used for quantitative analysis of the chemical concentration.
Preparation of tungstophosphoric acid-active carbon
catalysts: The preparation of tungstophosphoric acid-active
carbon catalysts was carried out as following steps. Firstly, a
certain amount of activated carbon was treated with diluted
HCl solution to remove the alkaline substances on its surface.
Activated carbon was then filtrated and washed several times
with deionized water until there is no Cl- in the eluent. After
being dried at 120 °C for 2 h, a certain amount of activated
carbon was added into H3O40PW12 solution, which was then
heated under reflux for 3.5 h. Unloaded H3O40PW12 was cleared
with water. Tungstophosphoric acid-active carbon catalysts
were obtained after being drying at 120 °C . Activation of the
catalysts at 150 °C for 2 h was carried out before being used.
Reactive distillation apparatus and process: The reactive
distillation experiments were carried out in a column with
vacuum jacket, which included stripping section (250 mm),
reaction section (500 mm) and rectifying section (100-450
mm). All the inner diameter of three parts was 20 mm. The
stripping section and rectifying section were embedded with
glass packing (3 × 16 mm), while the reaction section was
embedded with staggered mixture of glass packing and
Tungstophosphoric acid-Active carbon catalysts-containing
metal gauze bag.Average loading of the catalyst for each catalyst
bag was about 1.8 g.
15
20
25
30
35
40
45
Loading capacity (%)
Fig. 1. Influence of PW12 loadings capacity on the conversion of acidic acid
Between the ranges of 18-33 %, the conversion rate increased
linearly with the increasing of catalyst loading. More catalyst
loading (38 and 45 %), however, resulted in a decline in
conversion rate. Adsorption of H3O40PW12 on activated carbon
was physical adsorption, namely multi-molecular adsorption,
in which, excessive loading capacity could not increase the
catalytic performance when single molecular adsorption is
saturated. Thus, 33 % was determined as optimal catalyst loading
capacity in the following semi-continuous reactive distillation.
It was well known that the special Keggin structure was
needed for the activity of H3O40PW12. Therefore, IR was applied
to determine the retention of Keggin structure after being
loaded on the carbon. Fig. 2 depicted the comparison of the
IR spectrum of PW12 before and after being loaded on activated
carbon. It could be observed from Fig. 2 that four peaks of
1080, 980, 890 and 805 cm-1 were responsible for P-Oa, W-Od,
W-Ob-W and W-Oc-W, respectively, which indicated the
Keggin structure still existed in tungstophosphoric acid-active
carbon catalysts.
This device was operated with a semi-continuous form,
in which excessive methanol was charged into the bottom of
the column one time. Reboiler was then heated for a certain
time until the reflux was stable. After that, acidic acid aqueous
solution was fed into the column at the top of reaction section
continuously. Countercurrent contacting between methanol
and acidic acid happened on all the trays through the column.
At the top of rectifying section, methyl acetate was withdrawn
under certain reflux ratio along with water and unreacted
methanol. In the whole process, the column was insulated with
fiber glass to minimize heat losses.
1
RESULTS AND DISCUSSION
2
Optimization of loading capacity: Loading capacity of
H3O40PW12 on activated carbon was a key variable for reactive
distillation. The effect of catalyst loading on the conversion
of acidic acid was investigated firstly in batch distillation under
the condition of Mol(MeOH)/(CH3COOH) 2:1, temperature
70 °C and reaction time 3 h. Fig. 1 showed that 33 % catalyst
loading gave the best conversion rate (96.26 %) of acidic acid.
2200 2000 1800 1600 1400 1200 1000 800
Wave number (cm–1)
600
400
Fig. 2. IR spectrum of PW12 before (1) and after (2) being loaded on
activated carbon

Vol. 26, No. 21 (2014)
Effective Recovery of Acetic Acid from Wood Vinegar by Reactive Distillation 7313
90
80
70
60
50
90
72
54
36
18
0
Effect of feed velocity on reactive distillation: Fig. 3
showed the results obtained at five levels (30, 45, 60, 75 and
85 g/h) of aqueous solution of acidic acid feed velocity under
the conditions of rectifying section height 250 mm, reflux ratio
11:1 and rising steam quantity 114 g/h. As shown in Fig. 3,
the conversion was highest (80.52 %) when the feed velocity
was 30 g/h. A downward trend of acidic acid conversion
presented when the feed velocity increased from 45 to 85 g/h,
which was caused by the decreased contact time on tungsto-
phosphoric acid-active carbon catalyst. While the concentration
of methyl acetate increased in the withdrawn fraction. Taking
into account the processing capacity and effectiveness, 60 g/h
was chosen as the optimal feed velocity for wood vinegar.
1
2
3
4
HOAc
MeOAc
MeOH
H2O
3
1
2
4
80
100
120
140
160
180
Vapor velocity (g/h)
100
90
80
70
60
50
100
80
60
40
20
0
Fig. 4. Effect of MeOH vapor velocity on RD, 1 conversion of HOAc; 2,
3, 4 the distillate composition of MeOAc, MeOH and H2O
1
2
3
4
HOAc
MeOAc
MeOH
H2O
72
69
66
63
60
100
80
60
40
20
0
3
2
1
3
2
1
1
2
3
4
HOAc
MeOAc
MeOH
H2O
4
30
40
50
60
70
80
Feed velocity (g/h)
4
Fig. 3. Effect of diluted acidic acid feed velocity on reactive distillation, 1
conversion of HOAc; 2, 3, 4 the distillate composition of MeOAc,
MeOH and H2O
100
150
200
250
300
400
350
450
Rectifying section height (mm)
Fig. 5. Effect of rectifying section height on reactive distillation. 1
conversion of HOAc; 2, 3, 4 the distillate composition of MeOAc,
MeOH and H2O
Effect of methanol vapor velocity on reactive distillation:
Methanol vapor velocity was also investigated under the
conditions of rectifying section height 250 mm, reflux ratio
11:1 and acidic acid aqueous solution feed velocity 60 g/h.
Results obtained were presented as Fig. 4, which indicated
that the conversion increased from 58.44 to 72.07 % in the
given range of 84-175 g/h of MeOH vapor velocity. While the
concentration of methyl acetate decreased from 55.16 to
28.24 %. This result was consistent with the study of Sandesh
et al.19, in which, it was explained that the increasing of MeOH
vapor velocity could change the hydrodynamic behaviour of
the gas-liquid system. A compromise result of 67.96 % for
conversion rate and 41.26 % for methyl acetate concentration
was obtained at 114 g/h.
alcohol and ester. Therefore, 250 mm was selected as the
optimal rectifying section height.
Effect of reflux ratio on reactive distillation: Reflux
ratio was also optimized under the conditions of acidic acid
aqueous solution feed velocity 60 g/h, MeOH vapor rate 114
g/h, rectifying section height 250 mm and the result was
presented in Fig. 6. As shown in Fig. 6, a continuing decline
(from 74.57 to 62.04 %) of conversion appeared with the
increasing reflux ratio.Alcohol and ester concentration achieved
the minimum value (58.69 %) and the maximum (41.26 %),
respectively at the reflux ratio 11:1. It indicated that increasing
reflux ratio could enhance separation efficiency, however,
reduce the withdrawing rate, which inhibited the positive
reaction greatly. Process efficiency being considered, 9:1 was
selected as the optimal ratio.
Effect of rectifying section height on reactive distillation:
Fig. 5 presented the influence of rectifying section height on
the reactive distillation in the conditions of acidic acid aqueous
solution feed velocity 60 g/h, MeOH vapor rate 114 g/h, reflux
ratio 11:1. It showed that the conversion of acidic acid was
affected greatly by rectifying section height and the highest
conversion rate (67.96 %) was obtained at 250 mm. For with-
drawn product, the concentration of methyl acetate increased
slightly, while MeOH decreased with the increasing of recti-
fying section height. Overall, there was little change for the
composition of top withdrawn, which might be caused by the
excessive methanol and the similarity of boiling point between
Under a certain reactive distillation condition, a balance
should be established firstly before withdraw from the top.
Therefore, the time required to form a stable state in reactive
distillation was studied in this paper. It could be seen from
Fig. 7 that the top temperature and the concentration of methyl
ester in withdrawn product achieved a balance in 60 min. The
top temperature and the concentration of methyl ester were
58.2 °C and 41 %, respectively.

7314 Li et al.
Asian J. Chem.
TABLE 1
CONVERSION RATE OF ACETIC ACID IN WOOD VINEGAR AND THE OVERHEAD COMPONENT ANALYSIS
Top withdraw composition Wt%
Conversion of CH3COOH %
No.
Methyl acetate
H2O
0.51
0.33
0.39
0.41
CH3OH
56.76
56.67
57.02
56.82
Methyl propionate
1
71.85
72.03
71.94
71.94
41.03
1.70
1.60
1.64
1.65
2
41.40
3
40.95
Mean value
41.12
80
75
70
65
60
55
95
0.41 and 56.82 %, respectively. In addition of methyl acetate,
methyl propionate was also detected in the product with a
concentration of 1.65 %.
1
2
3
4
HOAc
MeOAc
76
MeOH
Conclusion
H2O
3
A reactive distillation method using tungstophosphoric
acid-active carbon as catalyst was developed for the recovery
of acidic acid from wood pyrolysis by-products called wood
vinegar. Tungstophosphoric acid-active carbon catalyst was
first prepared and then the loading capacity, feed flow rate,
MeOH vapor rate, rectifying section height and reflux ratio
were optimized. Optimal conditions were loading capacity
33%, feed flow rate 60 g/h, MeOH vapor rate 114 g/h, recti-
fying section height 250 mm and reflux ratio 9:1. Under this
condition, the optimal conversion of 71.94 % was obtained.
57
1
38
19
0
2
4
50
7
8
9
10
Reflux ratio
11
12
13
Fig. 6. Effect of reflux ratio on reactive distillation, 1 conversion of HOAc;
2, 3, 4 the distillate composition of MeOAc, MeOH and H2O
REFERENCES
1. L.G. Wei, B.W. Lu, Y.C. Ma and Z.Y. Li, Chem. Ind. Forest. Prod., 31,
12 (2011).
50
2. Y.X. Li and H.W. Lin, J. Anal. Sci., 28, 58 (2012).
3. S.J. Wang and K.J. Huang, Chem. Eng. Process., 60, 65 (2012).
4. H. Demiral and M.E. Yildirim, Water Sci. Technol., 47, 183 (2003).
5. R.P. Bhatt and S.B. Thakore, Int. J. Sci. Eng. Technol., 1, 46 (2012).
6. C C.-H. Shin, J.-Y. Kim, J.-Y. Kim, H.-S. Kim, H.-S. Lee, D. Mohapatra,
J.-W. Ahn, J.-G. Ahn and W. Bae, J. Hazard. Mater., 162, 1278 (2009).
7. P. Kalaichelvi, M. Perumalsamy, A. Arunagiri and K. Sofiya, J. Univ.
Chem. Technol. Metall., 42, 291 (2007).
63
40
62
30
61
Temperature
MeOAc
1
2
8. S.Y. Cheng and W. Huang, Coal Chem. Ind. J., 5, 9 (2010).
9. V. Ragaini, C.L. Bianchi and C. Pirola, Chem. Eng. J., 131, 257 (2007).
10. Z. Xu,A.Afacan and K.T. Chuang, Can. J. Chem. Eng., 77, 676 (1999).
11. R. Kumar and S.M. Mahajani, Ind. Eng. Chem. Res., 46, 6873 (2007).
12. W.-J. Hung, I.-K. Lai,Y.-W. Chen, S.-B. Hung, H.-P. Huang, M.-J. Lee
and C.-C. Yu, Ind. Eng. Chem. Res., 45, 1722 (2006).
13. Z.G. Zhang, X.F. Li, S.M. Xu and X.G. Li, Tianjin. Univ., 12, 264
(2006).
20
10
0
60
59
58
14. A. Singh, A. Tiwari, S.M. Mahajani and R.D. Gudi, Ind. Eng. Chem.
Res., 45, 2017 (2006).
0
20
40
60
80 100 120
Time (min)
140 160
15. T. Suman, S. Srinivas and S.M. Mahajani, Ind. Eng. Chem. Res., 48,
9461 (2009).
Fig. 7. Equilibrium curves between top temperature, methyl ester content
and time
16. Y.H. Li, S.B. Yu, X.G. Yuan and H. Wang, Ind. Eng. Chem. Res., 41,
4936 (2002).
Application of the method for wood vinegar: The optimal
method had been applied to recovery of acidic acid from raw
wood vinegar under above optimized conditions. Withdrawn
of the top product was started after 60 min. Three replications
were carried out and the results were given in Table-1. It showed
that the mean conversion of acidic acid was 71.94 % and the
mean concentration of MeOAc, H2O and MeOH were 41.12,
17. Y. Li, W. Chu, M.H. Chen and J.Y. Hu, J. Wuhan, Univ. Technol. (Mater.
Sci. Ed.), 2, 234 (2008).
18. H. Atia, U. Armbruster and A. Martin, Appl. Catal. A, 393, 331 (2011).
19. K. Sandesh, P.E. JagadeeshBabu, S. Math and M.B. Saidutta, Ind. Eng.
Chem. Res., 52, 6984 (2013).