This article was downloaded by: [George Mason University] On: 26 December 2014, At: 18:44 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Recovery of gallic acid from gallic acid processing wastewater a
a
a
a
Yundong Wu , Kanggen Zhou , Shuyu Dong , Wei Yu & Huiqing Zhang
a
a
School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, People's Republic of China Accepted author version posted online: 24 Sep 2014.Published online: 03 Oct 2014.
Click for updates To cite this article: Yundong Wu, Kanggen Zhou, Shuyu Dong, Wei Yu & Huiqing Zhang (2014): Recovery of gallic acid from gallic acid processing wastewater, Environmental Technology, DOI: 10.1080/09593330.2014.957246 To link to this article: http://dx.doi.org/10.1080/09593330.2014.957246
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 http://dx.doi.org/10.1080/09593330.2014.957246
Recovery of gallic acid from gallic acid processing wastewater Yundong Wu, Kanggen Zhou ∗ , Shuyu Dong, Wei Yu and Huiqing Zhang School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, People’s Republic of China
Downloaded by [George Mason University] at 18:44 26 December 2014
(Received 3 March 2014; final version received 17 August 2014 ) In this paper, an extraction technology has been investigated to recover gallic acid (GA) from GA processing wastewater. The effects of phase ratio and pH on the extraction behaviour of tributyl phosphate (TBP)/kerosene were investigated using TBP as the extractant and kerosene as the diluent. Our results showed that using 30% TBP, equilibrium was reached in 1 min. Extraction yields could be improved by increasing the phase ratio (organic phase:aqueous phase). The optimum pH values for the extraction and stripping processes were 3 and 6–9, respectively. The different GA concentrations had no noticeable effects on the distribution ratio between the organic phase and the aqueous phase during the extraction and stripping processes. The extraction yield that resulted from using the six-stage concentrating extraction was greater than 93%, with a phase ratio of 1:1 and an initial pH of 0.6. The GA concentration in the four-stage stripping liquor was greater than 100 g L−1 . Overall, the results indicated that the recovery of GA from GA processing wastewater is feasible using the methods described in this paper. Keywords: TBP; wastewater; gallic acid; extraction; stripping
1. Introduction Gallic acid (GA) (Figure 1) is a naturally occurring polyphenolic compounds that is widely used in biology, medicine, chemicals, dyes, electronics, the light industry and other fields,[2] and it has anti-inflammatory, antimutagenic, antioxidant, anti-free radical and other biological activities.[3] GA and its derivatives have been used to treat a variety of diseases. Recently, GA has been shown to prevent the formation and progression of cancer,[4,5] which has caused widespread concern. The methods for producing GA include acid, alkali, biological or enzymatic processes. Generally, manufacturers use the alkali process to produce GA, with gall as a raw material. This research was aimed to recover GA from wastewater that was generated from the alkali process, which contained up to 17 g L−1 GA, with high chemical oxygen demand (COD) concentration (60,000 mg L−1 ), high salinity (100 g L−1 ), high chroma (seal brown) and strong acidity (pH < 1.0). The pollutant composition was complicated with poor biodegradability and was difficult to manage for safe discharge. Currently, there is no proper treatment that ensures emission compliance. Because the GA concentration was low in the wastewater, it was difficult to recover using conventional means.[6] Thus, the wastewater is usually neutralized before discharge, because GA exhibits microbial inhibitory activities,[7] the wastewater can seriously damage the local ecological environment.
*Corresponding author. Email: [email protected] © 2014 Taylor & Francis
Because gall tannin is an ester that consists of 10 units of gallic acid (GA) and 1 unit of glucose,[8] the COD in GA processing wastewater is mainly composed of GA and glucose. As an important pharmaceutical intermediate, the economic value of GA is great, and the recovery of GA from wastewater could not only allow for recycling of the resource, but could also improve the biodegradability of the wastewater because most of the remaining COD was glucose, which could make the subsequent bio-treatment much easier. Scholars have performed a significant amount of research to recover GA. For example, Spigno et al. tried to recover GA using colloidal gas aphrons (CGA), which gained a maximum recovery rate of 63%,[9,10] In addition, Puoci et al. selectively recovered 80% of GA in olive oil wastewater with molecularly imprinted polymer microparticles.[11] He et al. studied the mechanisms of GA adsorption to resin, then desorption with a 70%
(a)
(b) O
HO
OH
HO OH
(c) O
-O
O
-O
OH -O
HO OH
OH OH
Figure 1. Chemical structure of (a) GA, (b) GA− and (c) GA2− .[1]
Downloaded by [George Mason University] at 18:44 26 December 2014
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ethanol solution which resulted in a recovery rate 85%.[12] Nevertheless, the methods mentioned above were not suitable for recovering GA from wastewaters with complex compositions. Because GA easily dissolves in methanol, ethanol, ethyl acetate and other organic solvents,[13] it is possible to remove GA from wastewater by using solvent extraction. Due to high production yield and ease of operation, solvent extraction has been widely used. For example, Kallithraka et al. studied the extraction behaviour of ether, 70% acetone and methyl formate, and determined that 70% acetone worked the best.[14] In addition, Chen et al. used butanol as an extractant, and found that the recovery yield was 90% when using single-stage extraction.[15] Because the GA sodium only dissolves in the aqueous phase, by stripping with an alkaline solution, the GA extracted in the organic phase could be transformed into GA sodium and then dissolve in the aqueous phase so as to be recovered. Yu et al. studied the recycling process with methyl isobutyl ketone (MIBK), and observed a total recovery rate of 95%.[16] However, the loss of MIBK was too large because its solubility in the wastewater was 2%, and its high cost and low flammability make its actual recovery difficult. The solubility of tributyl phosphate (TBP) in water is 0.6%, TBP is a common extractant that is widely used in the separation of rare-earth elements.[17–19] Kerosene was always added for diluting TBP which has a density that is similar to the density of water.[20,21] In this research, the extraction and stripping behaviours of TBP/kerosene were studied, the desired recovery rate was achieved, and a reliable recovery process was developed.
2. Materials and methods 2.1. Chemicals and reagents Analytical-grade TBP, kerosene, GA, HCl, NaOH, phosphoric acid and methanol were used in this study. The actual GA processing wastewater was obtained from a biotechnology company in Hunan province, China.
2.2.
Analysis methods
High-performance liquid chromatography (HPLC) was used to analyse the GA concentrations in the aqueous phase.[14,22,23] Meanwhile, the GA concentrations in the organic phase were calculated by using the following equation: (Ca − C a )Va Co = Vo (Co represents the GA dissolved in the organic phase. Ca and Ca represent the GA dissolved in the aqueous phase before and after extraction in mg·L−1 , and Vo and Va represent the volumes of organic and aqueous phases in L−1 ). The distribution ratio (D) was calculated as follows: D = (CW − CR /CR ) (CW represents the GA in the original wastewater and CR represents the GA in the wastewater after treatment by extraction). HPLC was performed using a G1311 A pump, a G-1322A vacuum degasser, a G-1313A autoinjector, a G-1314A VWD detector and an Agilent 1100 LC spectrophotometric detector that operated at 272 nm. A Diamonsil C18 (250 mm × 4.0 mm, 5 μm) column was used, the column temperature was held at 298 K and an injection volume of 5.0 μL. The mobile phase was methanol and 0.05% phosphoric acid (5:95) and was run at a flow rate of 1.0 mL min−1 . 2.3. Experimental set-up The simulated GA solution was used in the pH and extraction isotherm experiment, and the actual wastewater was used in the multistage extraction and stripping experiment. Experiments were conducted at a temperature of 303 K. First, the TBP/kerosene and GA solution or GA processing wastewater was mixed in extractors at a certain phase ratio, then after 10 min of oscillation, the extractors were left undisturbed to allow for the stratification of the two phases. Next, the GA concentrations in the aqueous phase were analysed. A flowchart of six-stage extraction and four-stage stripping is shown in Figure 2. The equipment used for the multistage extraction and stripping
strip strip liquor liquor
wastewater one-stage one-stage extraction extraction two-stage two-stage extraction extraction
one-stage stripping
NaOH
three-stage extraction
two-stage stripping
NaOH
four-stage extraction
three-stage stripping
NaOH
five-stage extraction
four-stage stripping
NaOH
six-stage extraction raffinate
deionizedwater organic phase aqueous phase
Figure 2. ① Flowchart of multistage extraction and stripping and ② pilot-scale equipment.
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processes was a pilot-scale equipment, with an extraction tank of 1800 × 1500 × 1000 mm and a stripping tank of 1200 × 1500 × 1000 mm. NaOH solution was used as the stripping agent. The volumes of aqueous and organic phase in both the extraction tank and the stripping tank were controlled at a 1:1 ratio. The flow of the wastewater and extractant was 200 L h−1 , while the flow of strip liquor was 30 L h−1 . During the first 25 h, the outlet of the stripping tank’s aqueous phase was pumped to the inlet so as to concentrate GA. After GA in the strip liquor reached 100 g·L−1 , the stripping tank was run at a phase ratio of 1:6.5.
80
60 3 40 2 20
1 Extration yield Distribution ratio
0 0
3. Results and discussion 3.1. The effects of the proportion of TBP on the extraction and stripping behaviours
Figure 3.
100
200
300 400 Time (s)
500
0 600
Extraction yield and distribution ratio with time. 10
100
A series of TBP/kerosene solutions was prepared to investigate the effects of the proportion of TBP on extraction and stripping behaviours. After extraction, equal volumes of a 0.2 mol L−1 NaOH solution were added into the loaded organic phase for stripping. The extraction and stripping distribution ratios and the extraction yield increased as the rate of TBP increased and as the stripping yield decreased (Table 1). Although the extraction yield was high when the TBP content was 40–100%, we found that it took a long time for stratification to occur during the experiment. In addition, the third phase would generate and float between the two phases, which were difficult to separate. When the TBP proportion was 30%, the density of the organic phase was 0.8239 g ml−1 , the two phases were stratified more quickly, and the extraction and stripping yields were high; therefore, no third phase was generated. Thus, 30% TBP/kerosene was selected for the subsequent experiments.
Extraction yield Distribution ratio
8
80
6
70 4
Distribution ratio
90 Extraction yield (%)
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Distribution ratio
Extration yield (%)
4
60 2 50 0 0
0.5
1.0
1.5 Vo: Va
2.0
2.5
3.0
Figure 4. The impact of the phase ratio on the extraction equilibrium (Vo : volume of the organic phase, and Va : volume of the aqueous phase).
3.3.
The impact of the phase ratio on the extraction equilibrium The extraction yield and distribution ratio both increased as the phase ratio was increased (Figure 4). Because the extraction capacity of the extractant is fixed, the extraction yield would increase as the phase ratio was increased. Thus, when the phase ratio was changed from 1:3 to 3:1,
3.2.
The impact of the reaction time on the extraction equilibrium The extraction yield and distribution ratio were less affected by the extraction time. The extraction yield and distribution ratio became stable by 1 min, indicating that the reaction proceeded rapidly (Figure 3). Table 1. TBP (%) 20 30 40 50 60 70 80 100
Effects of the proportion of TBP on extraction and stripping. Density g·ml−1
Extraction yield (%)
Extraction distribution ratio
Stripping yield (%)
Stripping distribution ratio
0.8103 0.8239 0.8494 0.8697 0.8768 0.9021 0.9179 0.9766
62.366 81.684 88.503 91.644 93.783 94.786 95.856 97.062
1.657 4.460 7.698 10.968 15.086 18.179 23.129 33.037
94.10 90.48 70.47 56.58 43.37 33.507 24.761 14.783
0.063 0.112 0.427 0.77 1.311 1.984 3.039 5.764
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the extraction yield and distribution ratio were increased by 1.76 and 1.77 times, respectively. 3.4.
The effects of the equilibrium pH on the extraction equilibrium Because GA has four pK a values (carboxyl group pK a1 4.16, hydroxyl groups pK a2 8.55, pK a3 11.40 and pK a4 12.80 [24]), GA ionized in the aqueous phase as follows: −
The highest equilibrium pH in our experiment was 10.36, which was lower than pK a3 − 1. Thus, only GA, GA− and GA2− existed in the aqueous phase throughout this study. When the equilibrium pH was below 3.16, we expected GA to only exist in the aqueous phase, while the distribution ratios of 10 and 1 g L−1 were 4.72 (SD = 0.10) and 8.09 (SD = 0.04), respectively. When the equilibrium pH was between 3.16 and 7.55, we expected GA/GA− and GA− to exist. However, as the pH was increased, the distribution ratio of the GA− concentration was likely to increase. When the equilibrium pH was greater than 7.77, the GA was likely to transform into GA− /GA2− and GA2− , which cannot be extracted. Consequently, the distribution ratio was very low. The distribution ratio increased slightly with pH under alkaline conditions in this experiment. However, the distribution ratio should not increase when GA− and GA2− cannot be extracted. Because the GA was not stable under alkaline conditions,[25] it was easily degraded. In addition, because part of the GA in the original aqueous phase was degraded during extraction or stripping, the distribution ratio should be larger than that shown in Figure 5. When the equilibrium pH was below 3.16, the distribution ratio was greater than 4.5, which indicated that the GA could be fully extracted in the organic phase. The distribution ratio was less than 0.3 when the equilibrium pH was greater than 6, which indicated that the GA
3.5. Extraction isotherms A series of GA solutions was prepared, and the pH was adjusted to 0.6, 1.5, 2.7, 7, 8 and 9. After extraction at a phase ratio of 1:1, the GA concentrations in the two phases were analysed. The isotherms are presented with the GA concentration in the aqueous phase as the abscissa, and the organic phase as the values on the vertical axis (Figures 6 and 7). When the pH was constant, the effects of the GA concentration on the extraction and stripping processes were
10000
slope=5.006 R 2 = 0.9
8000 slope=5.086 R 2 = 0.9 6000
slope = 4.816 R 2 = 0.9
4000 pH = 0.6 2000
pH = 1.5 pH = 2.7
0 0
Figure 6.
10
500 1000 1500 GA in aqueous phase(mg·L–1)
2000
Extraction isotherms of GA at pH 0.6, 1.5 and 2.7.
2000 [GA]=1g·L–1
pH = 7 GA in organic phase(mg·L–1)
8 Distribution ratio
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GA ↔ GA− + GA2 + GA3− + GA4− + nH + .
could be effectively stripped under wide pH conditions. To achieve optimum results, the equilibrium pH of the strip liquor should be controlled between 6 and 9. According to our results, extracting GA from actual wastewater with an equilibrium pH of < 3.16 would achieve a high extraction yield. The actual wastewater could be extracted directly. In this study, actual wastewater was extracted without a pH adjustment because its pH was 0.6, and the pH of the strip liquor was controlled at 8 ± 0.3 during the stripping process.
GA in aqueous phase (mg·L–1)
4
[GA]=10g·L–1
6
4
2
pH = 8
1500
pH = 9 slope = 0.097 R 2 = 0.9
1000
500 slope = 0.055 R 2 = 0.9
0
0 0
2
4
6 8 Equilibrium pH
10
12
Figure 5. Distribution ratios under different equilibrium pH.
slope = 0.200 R 2 = 0.9
0
Figure 7.
2000
4000 6000 8000 GA in aqueous phase(mg·L–1)
10,000
Extraction isotherms of GA at pH 7, 8 and 9.
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Extration yield (%)
90
100 80
80
60
Extration yield
70
GA
40
60
20 0
50 0
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GA in strip liqour (g·L–1)
120
10
20
30 Time (h)
40
5
extraction and stripping equilibrium. The extraction yields of six-stage extraction was greater than 93%, and the GA in the strip liquor by four-stage stripping was high than 100 g L−1 . Our results showed that the valuable GA component in the actual processing wastewater could be effectively recovered by the extraction process. Funding This work was supported by the Strategic Project of Science and Technology of Hunan Province, China [Grant No 2014GK1059].
50
Figure 8. Results of the six-stage extraction and the four-stage stripping processes from the actual GA wastewater.
small, and the extraction equilibrium of the different initial GA concentrations had the same basic characteristics. The distribution ratios at pH 0.6, 1.5 and 2.7 were about 5, but were less than 0.2 at pH 7, 8 and 9. Because the extraction of GA with TBP was a physical process when the pH was below pK a1 − 1, the extraction process was easy because the GA solution did not ionise. When the pH was above pK a1 − 1, GA exists exclusively in the ionic form, which makes it difficult to extract. Consequently, the GA concentrations had little effect on the equilibrium regardless of whether the dissociation of GA was a primary factor. 3.6.
The continuous recovery of GA using the six-stage extraction and four-stage stripping procedures The average extraction yield was 93.7% during the 50 h of effective operation, and the extraction yield did not change significantly as the run time increased (Figure 8), which indicated that the extraction process was stable and suitable for recovering GA from the actual processing wastewater. After 25 h of concentrating, the continuous GA effluent was approximately 100 g L−1 , which can generate GA directly after acidification and crystallization or be used as the raw material during the hydrolysis step of the alkali process. 4. Conclusions This paper demonstrated the advantages of using TBP/kerosene as an extractant in the GA extraction process, which is currently not a common practice. The results showed that when the consistency of the TBP was 30%, optimum results were achieved when using 30% TBP and the time taken to reach equilibrium was 1 min. When the phase ratio increased, the extraction yield increased. The suitable pH for extraction was < 3. In addition, the GA was effectively recovered from the organic phase when the equilibrium pH was between 6 and 9. When the pH was fixed, the GA concentrations had no obvious effects on the
References [1] Okabe N, Kyoyama H, Suzuki M. Gallic acid monohydrate. Acta Crystallogr E. 2001;57:764–766. [2] Chang L, Zhang Z, Huang J, Xu H, Zhong C. Review on preparation and application of Gallic acid. Biomass Chem Eng. 2010;4:48–52. [3] Li X, Cui L, Zhu D. Progress of study on the biological effect of Gallic acid. China Pharmacist. 2004;7:767–769. [4] Kuo C-L, Lai K-C, Ma Y-S, Weng S-W, Lin J-P, Chung J-G. Gallic acid inhibits migration and invasion of SCC4 human oral cancer cells through actions of NF-κB, Ras and matrix metalloproteinase-2 and-9. Oncol Rep. 2014;32: 355–361. [5] Spilioti E, Jaakkola M, Tolonen T, Lipponen M, Virtanen V, Chinou I, Kassi E, Karabournioti S, Moutsatsou P. Phenolic acid composition, antiatherogenic and anticancer potential of honeys derived from various regions in Greece. PloS One. 2014;9:1–10. [6] Qin Q. Techniques for treatment and recovery of effluents, residues and wasted carbon from gallic acid production. J Chem Ind Forest Prod. 2000;34:15–20. [7] Luís Â, Silva F, Sousa S, Duarte AP, Domingues F. Antistaphylococcal and biofilm inhibitory activities of gallic, caffeic, and chlorogenic acids. Biofouling. 2014;30: 69–79. [8] Cao N, Fu Y, He J. Mechanical properties of gelatin films cross-linked, respectively, by ferulic acid and tannin acid. Food Hydrocolloids. 2007;21:575–584. [9] Spigno G, Dermiki M, Pastori C, Casanova F, Jauregi P. Recovery of gallic acid with colloidal gas aphrons generated from a cationic surfactant. Sep Purif Technol. 2010;71:56– 62. [10] Spigno G, Jauregi P. Recovery of gallic acid with colloidal gas aphrons(CGA). Int J Food Eng. 2005;1:1–10. [11] Puoci F, Scoma A, Cirillo G, Bertin L, Fava F, Picci N. Selective extraction and purification of gallic acid from actual site olive mill wastewaters by means of molecularly imprinted microparticles. Chem Eng J. 2012;198: 529–535. [12] He Z, Xia W. Preparative separation and purification of phenolic compounds from Canarium album L. by macroporous resins. J Sci Food Agric. 2008;88:493–498. [13] Daneshfar A, Ghaziaskar HS, Homayoun N. Solubility of gallic acid in methanol, ethanol, water, and ethyl acetate. J Chem Eng Data. 2008;53:776–778. [14] Kallithraka S, Garcia-Viguera C, Bridle P, Bakker J. Survey of solvents for the extraction of grape seed phenolics. Phytochem Anal. 1995;6:265–267. [15] Chen L, Zhang X. A study on extracting gallic acid by butanol. J Northwest Univ (Nat Sci Ed). 1999;29:403–405.
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[16] Yu W, Zhou K, Wu Y, Du H. Extration technology for recovery of gallic acid from galic mother liquor. CIESC Journal. 2013:1660–1664. [17] Pin C, Zalduegui JS. Sequential separation of light rareearth elements, thorium and uranium by miniaturized extraction chromatography: application to isotopic analyses of silicate rocks. Analytica Chim Acta. 1997;339:79–89. [18] Keshavarz Alamdari E, Darvishi D, Haghshenas D, Yousefi N, Sadrnezhaad S. Separation of Re and Mo from roastingdust leach-liquor using solvent extraction technique by TBP. Sep Purif Technol. 2012;86:143–148. [19] Patnaik P, Baba A, Nathsarma K, Subbaiah T. Separation of iron and zinc from manganese nodule leach liquor using TBP as extractant. Mineral Process Extr Metall. 2013;122:179–185. [20] Lane E. Performance and degradation of diluents for TBP and the cleanup of degraded solvents. Nuclear Sci Eng (US). 1963;17:620–625.
[21] Adya V, Sengupta A, Dhawale B, Rajeswari B, Thulasidas S, Godbole S. Recovery of americium from analytical solid waste containing large amounts of uranium, plutonium and silver. J Radioanal Nuclear Chem. 2012;291: 843–848. [22] Weidenhamer J, Li M, Allman J, Bergosh R, Posner M. Evidence does not support a role for gallic acid in Phragmites australis invasion success. J Chem Ecol. 2013;39:323–332. [23] Queimada AJ, Mota FL, Pinho SP, Macedo EA. Solubilities of biologically active phenolic compounds: measurements and modeling. J Phys Chem B. 2009;113:3469–3476. [24] Powell H, Taylor M. Interactions of iron (II) and iron (III) with gallic acid and its homologues: a potentiometric and spectrophotometric study. Aust J Chem. 1982;35:739–756. [25] Polewski K, Kniat S, Slawinska D. Gallic acid, a natural antioxidant, in aqueous and micellar environment: spectroscopic studies. Curr Top Biophys. 2002;26:217–227.
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Recovery of gallic acid from gallic acid processing wastewater a
a
a
a
Yundong Wu , Kanggen Zhou , Shuyu Dong , Wei Yu & Huiqing Zhang
a
a
School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, People's Republic of China Accepted author version posted online: 24 Sep 2014.Published online: 03 Oct 2014.
Click for updates To cite this article: Yundong Wu, Kanggen Zhou, Shuyu Dong, Wei Yu & Huiqing Zhang (2014): Recovery of gallic acid from gallic acid processing wastewater, Environmental Technology, DOI: 10.1080/09593330.2014.957246 To link to this article: http://dx.doi.org/10.1080/09593330.2014.957246
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 http://dx.doi.org/10.1080/09593330.2014.957246
Recovery of gallic acid from gallic acid processing wastewater Yundong Wu, Kanggen Zhou ∗ , Shuyu Dong, Wei Yu and Huiqing Zhang School of Metallurgy and Environment, Central South University, Changsha 410083, Hunan, People’s Republic of China
Downloaded by [George Mason University] at 18:44 26 December 2014
(Received 3 March 2014; final version received 17 August 2014 ) In this paper, an extraction technology has been investigated to recover gallic acid (GA) from GA processing wastewater. The effects of phase ratio and pH on the extraction behaviour of tributyl phosphate (TBP)/kerosene were investigated using TBP as the extractant and kerosene as the diluent. Our results showed that using 30% TBP, equilibrium was reached in 1 min. Extraction yields could be improved by increasing the phase ratio (organic phase:aqueous phase). The optimum pH values for the extraction and stripping processes were 3 and 6–9, respectively. The different GA concentrations had no noticeable effects on the distribution ratio between the organic phase and the aqueous phase during the extraction and stripping processes. The extraction yield that resulted from using the six-stage concentrating extraction was greater than 93%, with a phase ratio of 1:1 and an initial pH of 0.6. The GA concentration in the four-stage stripping liquor was greater than 100 g L−1 . Overall, the results indicated that the recovery of GA from GA processing wastewater is feasible using the methods described in this paper. Keywords: TBP; wastewater; gallic acid; extraction; stripping
1. Introduction Gallic acid (GA) (Figure 1) is a naturally occurring polyphenolic compounds that is widely used in biology, medicine, chemicals, dyes, electronics, the light industry and other fields,[2] and it has anti-inflammatory, antimutagenic, antioxidant, anti-free radical and other biological activities.[3] GA and its derivatives have been used to treat a variety of diseases. Recently, GA has been shown to prevent the formation and progression of cancer,[4,5] which has caused widespread concern. The methods for producing GA include acid, alkali, biological or enzymatic processes. Generally, manufacturers use the alkali process to produce GA, with gall as a raw material. This research was aimed to recover GA from wastewater that was generated from the alkali process, which contained up to 17 g L−1 GA, with high chemical oxygen demand (COD) concentration (60,000 mg L−1 ), high salinity (100 g L−1 ), high chroma (seal brown) and strong acidity (pH < 1.0). The pollutant composition was complicated with poor biodegradability and was difficult to manage for safe discharge. Currently, there is no proper treatment that ensures emission compliance. Because the GA concentration was low in the wastewater, it was difficult to recover using conventional means.[6] Thus, the wastewater is usually neutralized before discharge, because GA exhibits microbial inhibitory activities,[7] the wastewater can seriously damage the local ecological environment.
*Corresponding author. Email: [email protected] © 2014 Taylor & Francis
Because gall tannin is an ester that consists of 10 units of gallic acid (GA) and 1 unit of glucose,[8] the COD in GA processing wastewater is mainly composed of GA and glucose. As an important pharmaceutical intermediate, the economic value of GA is great, and the recovery of GA from wastewater could not only allow for recycling of the resource, but could also improve the biodegradability of the wastewater because most of the remaining COD was glucose, which could make the subsequent bio-treatment much easier. Scholars have performed a significant amount of research to recover GA. For example, Spigno et al. tried to recover GA using colloidal gas aphrons (CGA), which gained a maximum recovery rate of 63%,[9,10] In addition, Puoci et al. selectively recovered 80% of GA in olive oil wastewater with molecularly imprinted polymer microparticles.[11] He et al. studied the mechanisms of GA adsorption to resin, then desorption with a 70%
(a)
(b) O
HO
OH
HO OH
(c) O
-O
O
-O
OH -O
HO OH
OH OH
Figure 1. Chemical structure of (a) GA, (b) GA− and (c) GA2− .[1]
Downloaded by [George Mason University] at 18:44 26 December 2014
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ethanol solution which resulted in a recovery rate 85%.[12] Nevertheless, the methods mentioned above were not suitable for recovering GA from wastewaters with complex compositions. Because GA easily dissolves in methanol, ethanol, ethyl acetate and other organic solvents,[13] it is possible to remove GA from wastewater by using solvent extraction. Due to high production yield and ease of operation, solvent extraction has been widely used. For example, Kallithraka et al. studied the extraction behaviour of ether, 70% acetone and methyl formate, and determined that 70% acetone worked the best.[14] In addition, Chen et al. used butanol as an extractant, and found that the recovery yield was 90% when using single-stage extraction.[15] Because the GA sodium only dissolves in the aqueous phase, by stripping with an alkaline solution, the GA extracted in the organic phase could be transformed into GA sodium and then dissolve in the aqueous phase so as to be recovered. Yu et al. studied the recycling process with methyl isobutyl ketone (MIBK), and observed a total recovery rate of 95%.[16] However, the loss of MIBK was too large because its solubility in the wastewater was 2%, and its high cost and low flammability make its actual recovery difficult. The solubility of tributyl phosphate (TBP) in water is 0.6%, TBP is a common extractant that is widely used in the separation of rare-earth elements.[17–19] Kerosene was always added for diluting TBP which has a density that is similar to the density of water.[20,21] In this research, the extraction and stripping behaviours of TBP/kerosene were studied, the desired recovery rate was achieved, and a reliable recovery process was developed.
2. Materials and methods 2.1. Chemicals and reagents Analytical-grade TBP, kerosene, GA, HCl, NaOH, phosphoric acid and methanol were used in this study. The actual GA processing wastewater was obtained from a biotechnology company in Hunan province, China.
2.2.
Analysis methods
High-performance liquid chromatography (HPLC) was used to analyse the GA concentrations in the aqueous phase.[14,22,23] Meanwhile, the GA concentrations in the organic phase were calculated by using the following equation: (Ca − C a )Va Co = Vo (Co represents the GA dissolved in the organic phase. Ca and Ca represent the GA dissolved in the aqueous phase before and after extraction in mg·L−1 , and Vo and Va represent the volumes of organic and aqueous phases in L−1 ). The distribution ratio (D) was calculated as follows: D = (CW − CR /CR ) (CW represents the GA in the original wastewater and CR represents the GA in the wastewater after treatment by extraction). HPLC was performed using a G1311 A pump, a G-1322A vacuum degasser, a G-1313A autoinjector, a G-1314A VWD detector and an Agilent 1100 LC spectrophotometric detector that operated at 272 nm. A Diamonsil C18 (250 mm × 4.0 mm, 5 μm) column was used, the column temperature was held at 298 K and an injection volume of 5.0 μL. The mobile phase was methanol and 0.05% phosphoric acid (5:95) and was run at a flow rate of 1.0 mL min−1 . 2.3. Experimental set-up The simulated GA solution was used in the pH and extraction isotherm experiment, and the actual wastewater was used in the multistage extraction and stripping experiment. Experiments were conducted at a temperature of 303 K. First, the TBP/kerosene and GA solution or GA processing wastewater was mixed in extractors at a certain phase ratio, then after 10 min of oscillation, the extractors were left undisturbed to allow for the stratification of the two phases. Next, the GA concentrations in the aqueous phase were analysed. A flowchart of six-stage extraction and four-stage stripping is shown in Figure 2. The equipment used for the multistage extraction and stripping
strip strip liquor liquor
wastewater one-stage one-stage extraction extraction two-stage two-stage extraction extraction
one-stage stripping
NaOH
three-stage extraction
two-stage stripping
NaOH
four-stage extraction
three-stage stripping
NaOH
five-stage extraction
four-stage stripping
NaOH
six-stage extraction raffinate
deionizedwater organic phase aqueous phase
Figure 2. ① Flowchart of multistage extraction and stripping and ② pilot-scale equipment.
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processes was a pilot-scale equipment, with an extraction tank of 1800 × 1500 × 1000 mm and a stripping tank of 1200 × 1500 × 1000 mm. NaOH solution was used as the stripping agent. The volumes of aqueous and organic phase in both the extraction tank and the stripping tank were controlled at a 1:1 ratio. The flow of the wastewater and extractant was 200 L h−1 , while the flow of strip liquor was 30 L h−1 . During the first 25 h, the outlet of the stripping tank’s aqueous phase was pumped to the inlet so as to concentrate GA. After GA in the strip liquor reached 100 g·L−1 , the stripping tank was run at a phase ratio of 1:6.5.
80
60 3 40 2 20
1 Extration yield Distribution ratio
0 0
3. Results and discussion 3.1. The effects of the proportion of TBP on the extraction and stripping behaviours
Figure 3.
100
200
300 400 Time (s)
500
0 600
Extraction yield and distribution ratio with time. 10
100
A series of TBP/kerosene solutions was prepared to investigate the effects of the proportion of TBP on extraction and stripping behaviours. After extraction, equal volumes of a 0.2 mol L−1 NaOH solution were added into the loaded organic phase for stripping. The extraction and stripping distribution ratios and the extraction yield increased as the rate of TBP increased and as the stripping yield decreased (Table 1). Although the extraction yield was high when the TBP content was 40–100%, we found that it took a long time for stratification to occur during the experiment. In addition, the third phase would generate and float between the two phases, which were difficult to separate. When the TBP proportion was 30%, the density of the organic phase was 0.8239 g ml−1 , the two phases were stratified more quickly, and the extraction and stripping yields were high; therefore, no third phase was generated. Thus, 30% TBP/kerosene was selected for the subsequent experiments.
Extraction yield Distribution ratio
8
80
6
70 4
Distribution ratio
90 Extraction yield (%)
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Distribution ratio
Extration yield (%)
4
60 2 50 0 0
0.5
1.0
1.5 Vo: Va
2.0
2.5
3.0
Figure 4. The impact of the phase ratio on the extraction equilibrium (Vo : volume of the organic phase, and Va : volume of the aqueous phase).
3.3.
The impact of the phase ratio on the extraction equilibrium The extraction yield and distribution ratio both increased as the phase ratio was increased (Figure 4). Because the extraction capacity of the extractant is fixed, the extraction yield would increase as the phase ratio was increased. Thus, when the phase ratio was changed from 1:3 to 3:1,
3.2.
The impact of the reaction time on the extraction equilibrium The extraction yield and distribution ratio were less affected by the extraction time. The extraction yield and distribution ratio became stable by 1 min, indicating that the reaction proceeded rapidly (Figure 3). Table 1. TBP (%) 20 30 40 50 60 70 80 100
Effects of the proportion of TBP on extraction and stripping. Density g·ml−1
Extraction yield (%)
Extraction distribution ratio
Stripping yield (%)
Stripping distribution ratio
0.8103 0.8239 0.8494 0.8697 0.8768 0.9021 0.9179 0.9766
62.366 81.684 88.503 91.644 93.783 94.786 95.856 97.062
1.657 4.460 7.698 10.968 15.086 18.179 23.129 33.037
94.10 90.48 70.47 56.58 43.37 33.507 24.761 14.783
0.063 0.112 0.427 0.77 1.311 1.984 3.039 5.764
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the extraction yield and distribution ratio were increased by 1.76 and 1.77 times, respectively. 3.4.
The effects of the equilibrium pH on the extraction equilibrium Because GA has four pK a values (carboxyl group pK a1 4.16, hydroxyl groups pK a2 8.55, pK a3 11.40 and pK a4 12.80 [24]), GA ionized in the aqueous phase as follows: −
The highest equilibrium pH in our experiment was 10.36, which was lower than pK a3 − 1. Thus, only GA, GA− and GA2− existed in the aqueous phase throughout this study. When the equilibrium pH was below 3.16, we expected GA to only exist in the aqueous phase, while the distribution ratios of 10 and 1 g L−1 were 4.72 (SD = 0.10) and 8.09 (SD = 0.04), respectively. When the equilibrium pH was between 3.16 and 7.55, we expected GA/GA− and GA− to exist. However, as the pH was increased, the distribution ratio of the GA− concentration was likely to increase. When the equilibrium pH was greater than 7.77, the GA was likely to transform into GA− /GA2− and GA2− , which cannot be extracted. Consequently, the distribution ratio was very low. The distribution ratio increased slightly with pH under alkaline conditions in this experiment. However, the distribution ratio should not increase when GA− and GA2− cannot be extracted. Because the GA was not stable under alkaline conditions,[25] it was easily degraded. In addition, because part of the GA in the original aqueous phase was degraded during extraction or stripping, the distribution ratio should be larger than that shown in Figure 5. When the equilibrium pH was below 3.16, the distribution ratio was greater than 4.5, which indicated that the GA could be fully extracted in the organic phase. The distribution ratio was less than 0.3 when the equilibrium pH was greater than 6, which indicated that the GA
3.5. Extraction isotherms A series of GA solutions was prepared, and the pH was adjusted to 0.6, 1.5, 2.7, 7, 8 and 9. After extraction at a phase ratio of 1:1, the GA concentrations in the two phases were analysed. The isotherms are presented with the GA concentration in the aqueous phase as the abscissa, and the organic phase as the values on the vertical axis (Figures 6 and 7). When the pH was constant, the effects of the GA concentration on the extraction and stripping processes were
10000
slope=5.006 R 2 = 0.9
8000 slope=5.086 R 2 = 0.9 6000
slope = 4.816 R 2 = 0.9
4000 pH = 0.6 2000
pH = 1.5 pH = 2.7
0 0
Figure 6.
10
500 1000 1500 GA in aqueous phase(mg·L–1)
2000
Extraction isotherms of GA at pH 0.6, 1.5 and 2.7.
2000 [GA]=1g·L–1
pH = 7 GA in organic phase(mg·L–1)
8 Distribution ratio
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GA ↔ GA− + GA2 + GA3− + GA4− + nH + .
could be effectively stripped under wide pH conditions. To achieve optimum results, the equilibrium pH of the strip liquor should be controlled between 6 and 9. According to our results, extracting GA from actual wastewater with an equilibrium pH of < 3.16 would achieve a high extraction yield. The actual wastewater could be extracted directly. In this study, actual wastewater was extracted without a pH adjustment because its pH was 0.6, and the pH of the strip liquor was controlled at 8 ± 0.3 during the stripping process.
GA in aqueous phase (mg·L–1)
4
[GA]=10g·L–1
6
4
2
pH = 8
1500
pH = 9 slope = 0.097 R 2 = 0.9
1000
500 slope = 0.055 R 2 = 0.9
0
0 0
2
4
6 8 Equilibrium pH
10
12
Figure 5. Distribution ratios under different equilibrium pH.
slope = 0.200 R 2 = 0.9
0
Figure 7.
2000
4000 6000 8000 GA in aqueous phase(mg·L–1)
10,000
Extraction isotherms of GA at pH 7, 8 and 9.
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Extration yield (%)
90
100 80
80
60
Extration yield
70
GA
40
60
20 0
50 0
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GA in strip liqour (g·L–1)
120
10
20
30 Time (h)
40
5
extraction and stripping equilibrium. The extraction yields of six-stage extraction was greater than 93%, and the GA in the strip liquor by four-stage stripping was high than 100 g L−1 . Our results showed that the valuable GA component in the actual processing wastewater could be effectively recovered by the extraction process. Funding This work was supported by the Strategic Project of Science and Technology of Hunan Province, China [Grant No 2014GK1059].
50
Figure 8. Results of the six-stage extraction and the four-stage stripping processes from the actual GA wastewater.
small, and the extraction equilibrium of the different initial GA concentrations had the same basic characteristics. The distribution ratios at pH 0.6, 1.5 and 2.7 were about 5, but were less than 0.2 at pH 7, 8 and 9. Because the extraction of GA with TBP was a physical process when the pH was below pK a1 − 1, the extraction process was easy because the GA solution did not ionise. When the pH was above pK a1 − 1, GA exists exclusively in the ionic form, which makes it difficult to extract. Consequently, the GA concentrations had little effect on the equilibrium regardless of whether the dissociation of GA was a primary factor. 3.6.
The continuous recovery of GA using the six-stage extraction and four-stage stripping procedures The average extraction yield was 93.7% during the 50 h of effective operation, and the extraction yield did not change significantly as the run time increased (Figure 8), which indicated that the extraction process was stable and suitable for recovering GA from the actual processing wastewater. After 25 h of concentrating, the continuous GA effluent was approximately 100 g L−1 , which can generate GA directly after acidification and crystallization or be used as the raw material during the hydrolysis step of the alkali process. 4. Conclusions This paper demonstrated the advantages of using TBP/kerosene as an extractant in the GA extraction process, which is currently not a common practice. The results showed that when the consistency of the TBP was 30%, optimum results were achieved when using 30% TBP and the time taken to reach equilibrium was 1 min. When the phase ratio increased, the extraction yield increased. The suitable pH for extraction was < 3. In addition, the GA was effectively recovered from the organic phase when the equilibrium pH was between 6 and 9. When the pH was fixed, the GA concentrations had no obvious effects on the
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