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Influence of the diluent on the extraction of acetic acid from the prehydrolysis liquor of kraft based dissolving pulp production process by tertiary amine
Separation and Purification Technology 120 (2013) 341–345
Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Influence of the diluent on the extraction of acetic acid from the prehydrolysis liquor of kraft based dissolving pulp production process by tertiary amine Guihua Yang a,b,⇑, M. Sarwar Jahan a,c,⇑, Laboni Ahsan a, Yonghao Ni a,⇑ a b c
Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada Key Laboratory of Pulp & Paper Science and Technology (Qilu University of Technology), Ministry of Education, Jinan, Shandong 250353, China Pulp and Paper Research Division, BCSIR Laboratories, Dhaka, Dhaka 1205, Bangladesh
a r t i c l e
i n f o
Article history: Received 10 May 2013 Received in revised form 30 September 2013 Accepted 1 October 2013 Available online 21 October 2013 Keywords: Acetic acid Pre-hydrolysis liquor Tertiary amine Diluent 2-Ethyl-1-hexanol Recovery and regeneration
a b s t r a c t Different diluents including 1-decanol, 1-octanol and 2-ethyl-1-hexanol and kerosene have been evaluated in extracting acetic acid from the treated prehydrolysis liquor (TPHL) by triisooctylamine (TIOA) or trioctylamine (TOA). Diluent played an important role in recovering acetic acid from the TPHL, thus affecting the extraction equilibrium and extraction efficiency. Polar diluent like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance than the nonpolar diluent kerosene. The maximum extraction efficiency was 68.79%, which was from 2-ethyl-1-hexanol. The organic solvent was regenerated and extracted HAc was recovered by aqueous sodium hydroxide. The regeneration efficiency can be improved by increasing molar ratio of sodium hydroxide to HAc. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction It is now well established that the pre-hydrolysis liquor (PHL) of dissolving pulp production process is a good feedstock of a lignocelluloses biorefinery [1–4]. Acetic acid is one of the main components in the industrial PHL from a hardwood kraft-based dissolving pulp production process [3,5] and its concentration is about 1%. The recovery of acetic acid from the PHL is a promising opportunity in the path of green economy, and it can be recovered by distillation, liquid–liquid extraction, adsorption, membrane separation etc. For the distillation method, the dilute nature of the PHL would lead to very high energy cost. The reactive extraction was selected for the present investigation in considering its efficiency and selectivity from such a dilute solution [4]. It is reported that tertiary amine is the better extractant for the removal and recovery of carboxylic acid from industrial waste water [6–10]. Diluent is usually added along with the extractant to improve extraction power of the extractant by providing solvation and specific interaction. It was observed that the extraction ⇑ Corresponding authors. Address: Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada. Tel.: +1 5064516860 (M.S. Jahan). E-mail addresses: [email protected] (G. Yang), [email protected] (M.S. Jahan), [email protected] (Y. Ni). 1383-5866/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seppur.2013.10.004
efficiency of amine in the reactive extraction was significantly affected by the type of diluents [11]. Therefore, it is important to select an efficient diluent to improve extraction efficiency. The diluent may consist of one or more components, including aliphatic/aromatic hydrocarbons, ketones, higher alcohols. Sahin et al. [12] investigated the extraction of formic acid by a high molecular-weight aliphatic amine, tridodecylamine (TDA), and a phosphorus-bonded, oxygen-containing extractant, tributyl phosphate (TBP), dissolved in five different diluents (ethyl valerate, diethyl adipate, diethyl sebacate, 1-octanol, and heptane) and observed that combination of TDA and diethyl adipate had the highest distribution coefficient of 6. Tuyun and Uslu [13] studied different high alcohols, acetates, ketones for extracting picolinic acid by tridodecylamine and obtained the highest distribution coefficient for 1-octanol. Keshav et al. [14] investigated different diluents (n-heptane, petroleum ether, ethyl acetate and oleyl alcohol) for extracting propionic acid from a dilute aqueous solution by TOA. The highest extraction was found with TOA-oleyl alcohol. Qin et al. [15] studied on the extraction of different carboxylic acids by TOA in 1-octanol, chloroform, MIBK, tetrachloromethane and hexane to observe the effect of acid and effect of diluents. Extraction of different carboxylic acid using tri-n-butyl phosphate (TBP), tri-n-octyl amine (TOA) and their mixtures was investigated by Matsumoto et al. [11] and the synergism effect was highlighted
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in improving the extraction. For extracting acetic acid from the PHL, a suitable extraction and diluent need to be selected for getting maximum distribution coefficient. The main objective of this work was to evaluate the different diluents namely 1-decanol (D), 2-ethyl-1-hexanol (E), 1-octanol (O) and Kerosene (K), and mixture of D and K, E and K for extracting acetic acid from the PHL of the kraft based dissolving pulp production process. Two types of extractant: Trioctylamine (TOA), and triisooctylamine (TIOA) were assessed. The extracted acetic acid was also recovered and solvent was regenerated by sodium hydroxide stripping. 2. Experimental 2.1. Materials The industrial produced PHL sample was collected from the dissolving pulp mills in Eastern Canada. The PHL was filtered with Whatman qualitative filter papers and Nylon 66 membrane with a pore size of 0.45 lm (Supelco analytical group, USA) for removing large particles and impurities. Triisooctylamine (TIOA), trioctylamine (TOA), 2-ethyl-1-hexanol, 1-octanol, 1-decanol and kerosene were purchased from Sigma–Aldrich Co. (USA). CR325 W activated carbon was obtained from Carbon Resources Inc. (CA). Sulfuric acid was purchased from Fisher Scientific Inc. (USA). Sodium hydroxide (60 %wt) was obtained from Ricca Chemical Company (USA) and diluted to 5–30 %wt. for use.
Amine concentration was defined the percentage of corresponding amine by mass balance
%Amine concentration
W amine 100% W amine þ wDiluent
ð1Þ
The concentration of HAC in organic phase was determined by mass balance
½HAorg
eq
½HAaq V aq
initial
¼
½HAaq V aq
eq
ðV org Þaq
ð2Þ
where Vaq is the volume of aqueous phase (mL) and Vorg is the volume of organic phase (mL). For the evaluating extraction efficiencies of different runs, HAC recovery (%) and distribution coefficient (KD) were introduced. The percent weight of HAC transferred from the aqueous phase into organic phase was expressed the percentage recovery of corresponding HAC.
%Recovery ¼
ð½HAorg V org Þaq ð½HAaq V aq Þinitial
100%
ð3Þ
The equilibrium distribution coefficient (KD) was defined the ratio of the HAC weight fraction of organic phase (bHAcorg Vorg ) to that of aqueous phase (bHAcaq Vaq ) , at equilibrium.
KD ¼
½HAorg V org ½HAaq V aq
!
ð4Þ eq
2.2. Activated carbon treatment 2.7. Regeneration of tertiary amine and solvent/diluent The PHL was treated with activated carbon (AC) at room temperature and in sonication for 30 min. The weight ratio of PHL to AC was 20:1. 2.3. Sugar analysis The sugar content of the PHL was determined by using an Ion Chromatography unit equipped with CarboPac TM PA1 column (Dionex-300, Dionex Corporation, USA) and a pulsed amperometric detector (PAD). The details methods are described in elsewhere [16,17]. 2.4. Acetic acid and furfural analysis
The regeneration of amine and solvent/diluent was done by adding aqueous sodium hydroxide in organic phase for 20– 90 min at 1–4 M ratio of sodium hydroxide to HAc and shaking speed 200 rpm. Recovery of HAc by NaOH is based on the concentration of HAc in organic phase (Eq. (2)). The percent weight of HAc transferred from the organic phase into aqueous phase (sodium acetate) was expressed the percentage recovery of corresponding HAc.
½HAaq V aq eq % Recovery ¼ ½HAorg V org
100%
ð5Þ
initial
A Varian 300 NMR–spectrometer was employed for determining the furfural and acetic acid concentrations as methods described earlier [17].
3. Results and discussion
2.5. Lignin analysis
Diluent for tertiary amine plays an important role in the extraction process [9,11,18,19]. Therefore, selection of a suitable diluent is an important factor for extracting acetic acid from the PHL. Fig. 1 shows the extraction equilibrium of acetic acid from the TPHL by TIOA in different diluents at the mole ratio of 1. The degree of extraction of acetic acid with TIOA was in the order of 2-ethyl-1-hexanol (E) > E + 1-octanol (O) > 1-decanol (D) > D + E > D + O > O > E + kerosene (K) > D + K > K. The maximum extraction of 68.79% was obtained for 2-ethyl-1-hexanol while the minimum extraction was 13.36% only for kerosene. The lower extraction equilibrium of kerosene can be increased to 53.13% and 52.92% with the addition of decanol or 2-ethyl-1-hexanol in kerosene, respectively. The above results that polar diluents like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance in recovering acetic acid from the TPHL when extracted using TIOA, than the nonpolar diluent can be explained as follows. The salvation of
The UV/Vis spectrometric method at a wavelength of 205 nm (Tappi UM250) was used to measure the lignin content of PHL [16]. 2.6. Liquid–liquid extraction Required amount of the organic phase (tertiary amine and diluent or solvent) and aqueous solution (AC treated PHL samples) were charged in flasks separately. A extraction was performed by stirring by magnetic bar with heating at 400 rpm or shaking by shaker with heating at 200–300 rpm and varied temperature of 25–50 °C for the varied time of 5–15 min, and pH value of the AC PHL–amine mixture was adjusted by adding NaOH. Then the extraction mixture was centrifuged at 3000 rpm for 5 min to assist separation of organic and aqueous phases. The two phases were analyzed immediately after separation.
3.1. Effect of different diluents for tertiary amine
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Table 2 Effect of time, temperature and pH on the recovery of acetic acid from the activated carbon pre-treated PHL (molar ratio of TIOA/TOA to acetic acid of 1, 30% TIOA dilution). Time (min)
Fig. 1. Effect of different solvents for 30% TIOA concentration on recovery of acetic acid at molar ratio 1 (D – 1-decanol, E – 2-ethyl-1-hexanol, O – 1-octanol, K – Kerosene. For D + K or E + K solvents the weight ratio of D/E to K was 2. For D + E, E + O and D + O system, the weight ratio was 1).
2 4 8 10 12 10 10 10 10 10 10 10 10
Temperature (°C)
25 25 25 25 25 20 25 30 50 25 25 25 25
pH
4.5 (original) 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 5.0 5.5 6.5
Acetic acid recovery (%) TIOA
TOA
66.14 66.18 67.27 67.52 67.46 65.79 67.52 67.16 62.18 67.52 65.12 64.17 61.12
72.26 73.13 73.26 73.32 73.17 70.08 73.32 70.50 66.41 73.32 70.02 66.99 61.02
3.3. Effect of time, temperature and pH the complex by the diluents is one of the most important factors in extraction of carboxylic acid. A polar diluent increases the extracting power of nonpolar amines by providing additional solvating power that allows higher levels of polar acid–amine complexes to stay in the organic phase. Sahin et al. [12] observed that the solubility of acid–amine complex increases as the polarity of diluents increases. Especially, protic halogenated hydrocarbons and alcohol diluents, chloroform and 1-octanol, give an unusually high degree of extraction through the specific hydrogen bonding between the proton of the diluent and the acid–amine complex [20,21].
3.2. Effect of 2-ethyl-1-hexanol as diluent The amounts of TIOA and 2-ethyl-1- hexanol as the diluent, are critical in the extraction process and they need to be optimized. Effects of TIOA concentration and mole ratio on the recovery of acetic acid and distribution coefficient are shown in Table 1. It is seen from the Table 1 that the acetic acid recovery was increased with increasing molar ratio of TIOA, consequently increased equilibrium distribution coefficient KD. For example, at the molar ratio of 1, the acetic acid recovery was 67.4% with the TIOA concentration of 32%, it was 78.4% with the increase of molar ratio to 2 at the same dilution. The TIOA concentration (in 2-ethyl-1-hexanol) had only marginal effect on the extraction of acetic acid. Diluent influenced the formation of acid–amine complexes. And the dipole–dipole interactions between solvent and complex can promote the formation of acid–amine complex by the complex-solvent hydrogen bond [22]. Zhong et al. [23] studied the reactive extraction of propionic acid using alamine in 2-octanol and 1-dodecanol as diluents at various amine concentration (0–100%) and found extraction to be maximized at the amine concentration between of 20–40%. The diluted extractant gave much higher KD values [24]. In the subsequent study, a molar ratio of TIOA to HAc of 1, and the TIOA concentration of 30% were chosen.
The effects of time, temperature and pH on the extraction of acetic acid from the PHL by TIOA or TOA using 2-ethyl-1-hexanol as the diluent, are shown in Table 2. The extraction was carried out with tertiary amine at 30% concentration at 1 M ratio with varying time, temperature and pH and the results. It can be found that the recovery of acetic acid was reached to equilibrium within 10 min and the recovery reached 67% and 73% for TIOA and TOA at 25 °C, respectively. Similarly, a fast acetic acid extraction was observed from the bio-oil by TOA [8]. This fast reaction can be explained by the acid–base reaction during extraction process. A further increase of temperature from 25 to 50 °C, had a negative effect on the extraction efficiency, since the acetic acid recovery was decreased. The reason may be explained by the instability of acetic acid–amine complex and shifting of extraction equilibrium at higher temperature [25,26]. Table 2 also shows that the increase of pH from the initial mixture pH of 4.5 negatively affected the extraction efficiency of acetic acid, which complies with the conclusions of Yang et al. [27]. In summary, it can be concluded that the extraction process of acetic acid from PHL into diluted tertiary amine/2-ethyl-hexanol system can be completed within 10 min, optimal temperature for the recovery of acetic acid was 25 °C. The pH of the system should not increase. 3.4. Regeneration of amine and solvent Regeneration and reuse of amine and solvents/diluents in recovering acetic acid from the PHL would be desirable, and it was carried out by using sodium hydroxide. Sodium hydroxide reacted with acetic acid in HAc–amine complex to form sodium acetate, and subsequently TIOA/TOA and the diluent were regenerated. The regeneration was done by varying molar ratio of sodium hydroxide to HAc from 1 to 4, reaction time from 20 to 90 min and results are shown in Figs. 2 and 3. The acetic acid
Table 1 Effect of TIOA dilution by 2-ethyl-1-hexanol and molar ratio on the recovery of acetic acid from the activated carbon pre-treated PHL (extraction time, temperature and pH were 10 min, 20 °C and 4.5 respectively). Mole ratio/dilution
26 32 36
0.5
1.0
1.5
2.0
Recovery (%)
KD
Recovery (%)
KD
Recovery (%)
KD
Recovery (%)
KD
49.7 52.7 49.4
0.99 1.11 0.98
67.0 67.4 64.9
2.05 2.06 1.86
77.3 75.2 74.2
3.35 3.03 2.87
78.6 78.4 76.1
3.67 3.63 3.19
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time of regenerated solvent. After 4th time recycling of regenerated solvent, the HAc recovery was decreased by 2.55% and 1.54% for TIOA and TOA, respectively (Table 3). This lower recovery efficiency can be overcome by increasing the molar ratio. In the 4th time recycling of regenerated solvent, the recovery of HAc was increased from 63.03% to 66.01% for TIOA and with increasing molar ratio from 1 to 2. The reason for the lower extraction yield when using recycled solvent/diluent, may be due to the existence of a small amount lignin in the organic phase, which can hinder the HAc extraction. 4. Conclusions Fig. 2. Effect of regeneration time on the recovery of HAc (NaOH–HAc molar ratio, 1).
Compared to nonpolar diluent kerosene, polar diluents like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance in recovering acetic acid from the TPHL when extracted using TIOA. The lower extraction of acetic acid in kerosene can be improved by adding decanol or 2-ethyl-1-hexanol. The extraction process was very fast and its equilibrium was reached within 10 min at 25 °C. A higher pH increased the dissociation of acetic acid, as a result decreased the extraction yield of acetic acid. The molar ratio of NaOH to HAc played an important role in organic phase regeneration process and acetic acid recovery from the organic phase. Acknowledgements
Fig. 3. Effect of NaOH–HAc mole ratio on the recovery of HAc from the loaded organic phase (regeneration time 60 min).
Table 3 Effect of recycling of regenerated solvent and mole ratio on the recovery of HAc from the loaded organic (30% amine concentration at 1 M ratio and regeneration time 60 min). Ratio (mole)
1 1 1 1 1 2 2 2 4
Recycling (times)
1 2 3 4 1 2 3 4 5
HAc recovery (%) TIOA-E
TOA-E
65.58 64.05 63.69 63.03 65.58 66.87 66.37 66.01 67.38
68.48 68.17 67.43 66.94 68.48 71.62 69.75 68.66 72.49
recovery from the loaded organic phase was improved slightly with increasing regeneration time and molar ratio of NaOH to HAc. At the mole ratio of 1, HAc recovery as Na-acetate was increased from 63.01% to 65.58% for TIOA-E system and from 64.69% to 69.48% for TOA-E system with increasing reaction time from 20 min to 60 min, further increase of time did not increase HAc recovery significantly. It also can be seen that HAc recovery was increased from 65.58% to 67.89% for TIOA-E system and 68.48% to 72.69% for TOA-E sytem with the increase of mole ratio from 1 to 4. The effect of molar ratio was pronounced when recycle the regenerated solvent for further recovery of HAc from the loaded organic solvent (Table 3). The effect of recycling the regenerated solvent/ diluent on the HAc recovery of was also studied. As shown in Table 3, the HAc recovery yield was decreased slightly with increasing recycling
This project was funded by an NSERC CRD Grant. And the authors are also grateful for the financial support from the National Science Foundation of China (Grant Nos. 31070525, 31270627), and Taishan Scholar Program of Shandong Province (Grant No. 2605). References [1] L. Ahsan, M.S. Jahan, H. Liu, Y. Ni, Recovery of acetic acid from pre-hydrolysis liquor of the kraft based dissolving pulp production process by reactive extraction with tri-octyl amine (TOA) and octanol, J-FOR. 2 (4) (2012) 38–43. [2] H. Liu, H. Hu, M.S. Jahan, Y. Ni, Furfural formation from the pre-hydrolysis liquor of a hardwood kraft-based dissolving pulp production process, Bioresource. Technol. 131 (2013) 315–320. [3] A. Saeed, M.S. Jahan, H. Li, Z. Liu, Y. Ni, A. van Heiningen, Mass balances of components dissolved in the pre-hydrolysis liquor of kraft-based dissolving pulp production process from Canadian hardwoods, Biomass Bioenergy 39 (2012) 14–19. [4] G. Yang, M.S. Jahan, L. Ahsan, L. Zheng, Y. Ni, Recovery of acetic acid from prehydrolysis liquor of hardwood kraft-based dissolving pulp production process by reactive extraction with triisooctylamine, Bioresource. Technol. 138 (2013) 253–258. [5] H. Shi, P. Fatehi, H. Xiao, Y. Ni, Optimizing the poly ethylene oxide flocculation process for isolating lignin of prehydrolysis liquor of a kraft-based dissolving pulp production process, Ind. Eng. Chem. Res. 51 (2012) 5330–5335. [6] Y.K. Hong, W.H. Hong, Removal of acetic acid from aqueous solution containing succinc acid and acetic acid by tri-n-octylamine, Sep. Purif. Technol. 42 (2005) 151–157. [7] Z. Li, W. Qin, Y. Dai, Liquid–liquid equilibria of aqueous acetic acid derivatives with trioctylamine and select organic diluents, J. Chem. Eng. Data 48 (2003) 1113–1119. [8] F.H. Mahfud, F.P. Van Geel, R.H. Venderbosch, H.J. Heeres, Acetic acid recovery from fast pyrolysis oil – an exploration study on liquid–liquid reactive extraction using aliphatic tertiary amines, Separ. Sci. Technol. 43 (2008) 3056– 3074. [9] H. Uslu, Reactive extraction of formic acid by using trioctyl amine, Sep. Purif. Technol. 44 (2009) 1784–1789. [10] C.R. Vitasari, G.W. Meindersma, A.B. De Haan, Glycolaldehyde co-extraction during the reactive extraction of acetic acid with tri-n-octylamine/2-ethyl-1hexanol from a wood-based pyrolysis oil-derived aqueous phase, Sep. Purif. Technol. 95 (2012) 39–43. [11] M. Matsumoto, T. Otono, K. Kondo, Synergistic extraction of organic acids with tri-n octylamine and tri-n-butylphosphate, Sep. Purif. Technol. 24 (2001) 337– 342. [12] S. Sahin, S.S. Bayazit, M. Bilgin, I. I_nci, Investigation of formic acid separation from aqueous solution by reactive extraction: effects of extractant and diluents, J. Chem. Eng. Data 55 (4) (2010) 1519–1522.
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Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Influence of the diluent on the extraction of acetic acid from the prehydrolysis liquor of kraft based dissolving pulp production process by tertiary amine Guihua Yang a,b,⇑, M. Sarwar Jahan a,c,⇑, Laboni Ahsan a, Yonghao Ni a,⇑ a b c
Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada Key Laboratory of Pulp & Paper Science and Technology (Qilu University of Technology), Ministry of Education, Jinan, Shandong 250353, China Pulp and Paper Research Division, BCSIR Laboratories, Dhaka, Dhaka 1205, Bangladesh
a r t i c l e
i n f o
Article history: Received 10 May 2013 Received in revised form 30 September 2013 Accepted 1 October 2013 Available online 21 October 2013 Keywords: Acetic acid Pre-hydrolysis liquor Tertiary amine Diluent 2-Ethyl-1-hexanol Recovery and regeneration
a b s t r a c t Different diluents including 1-decanol, 1-octanol and 2-ethyl-1-hexanol and kerosene have been evaluated in extracting acetic acid from the treated prehydrolysis liquor (TPHL) by triisooctylamine (TIOA) or trioctylamine (TOA). Diluent played an important role in recovering acetic acid from the TPHL, thus affecting the extraction equilibrium and extraction efficiency. Polar diluent like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance than the nonpolar diluent kerosene. The maximum extraction efficiency was 68.79%, which was from 2-ethyl-1-hexanol. The organic solvent was regenerated and extracted HAc was recovered by aqueous sodium hydroxide. The regeneration efficiency can be improved by increasing molar ratio of sodium hydroxide to HAc. Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction It is now well established that the pre-hydrolysis liquor (PHL) of dissolving pulp production process is a good feedstock of a lignocelluloses biorefinery [1–4]. Acetic acid is one of the main components in the industrial PHL from a hardwood kraft-based dissolving pulp production process [3,5] and its concentration is about 1%. The recovery of acetic acid from the PHL is a promising opportunity in the path of green economy, and it can be recovered by distillation, liquid–liquid extraction, adsorption, membrane separation etc. For the distillation method, the dilute nature of the PHL would lead to very high energy cost. The reactive extraction was selected for the present investigation in considering its efficiency and selectivity from such a dilute solution [4]. It is reported that tertiary amine is the better extractant for the removal and recovery of carboxylic acid from industrial waste water [6–10]. Diluent is usually added along with the extractant to improve extraction power of the extractant by providing solvation and specific interaction. It was observed that the extraction ⇑ Corresponding authors. Address: Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada. Tel.: +1 5064516860 (M.S. Jahan). E-mail addresses: [email protected] (G. Yang), [email protected] (M.S. Jahan), [email protected] (Y. Ni). 1383-5866/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.seppur.2013.10.004
efficiency of amine in the reactive extraction was significantly affected by the type of diluents [11]. Therefore, it is important to select an efficient diluent to improve extraction efficiency. The diluent may consist of one or more components, including aliphatic/aromatic hydrocarbons, ketones, higher alcohols. Sahin et al. [12] investigated the extraction of formic acid by a high molecular-weight aliphatic amine, tridodecylamine (TDA), and a phosphorus-bonded, oxygen-containing extractant, tributyl phosphate (TBP), dissolved in five different diluents (ethyl valerate, diethyl adipate, diethyl sebacate, 1-octanol, and heptane) and observed that combination of TDA and diethyl adipate had the highest distribution coefficient of 6. Tuyun and Uslu [13] studied different high alcohols, acetates, ketones for extracting picolinic acid by tridodecylamine and obtained the highest distribution coefficient for 1-octanol. Keshav et al. [14] investigated different diluents (n-heptane, petroleum ether, ethyl acetate and oleyl alcohol) for extracting propionic acid from a dilute aqueous solution by TOA. The highest extraction was found with TOA-oleyl alcohol. Qin et al. [15] studied on the extraction of different carboxylic acids by TOA in 1-octanol, chloroform, MIBK, tetrachloromethane and hexane to observe the effect of acid and effect of diluents. Extraction of different carboxylic acid using tri-n-butyl phosphate (TBP), tri-n-octyl amine (TOA) and their mixtures was investigated by Matsumoto et al. [11] and the synergism effect was highlighted
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in improving the extraction. For extracting acetic acid from the PHL, a suitable extraction and diluent need to be selected for getting maximum distribution coefficient. The main objective of this work was to evaluate the different diluents namely 1-decanol (D), 2-ethyl-1-hexanol (E), 1-octanol (O) and Kerosene (K), and mixture of D and K, E and K for extracting acetic acid from the PHL of the kraft based dissolving pulp production process. Two types of extractant: Trioctylamine (TOA), and triisooctylamine (TIOA) were assessed. The extracted acetic acid was also recovered and solvent was regenerated by sodium hydroxide stripping. 2. Experimental 2.1. Materials The industrial produced PHL sample was collected from the dissolving pulp mills in Eastern Canada. The PHL was filtered with Whatman qualitative filter papers and Nylon 66 membrane with a pore size of 0.45 lm (Supelco analytical group, USA) for removing large particles and impurities. Triisooctylamine (TIOA), trioctylamine (TOA), 2-ethyl-1-hexanol, 1-octanol, 1-decanol and kerosene were purchased from Sigma–Aldrich Co. (USA). CR325 W activated carbon was obtained from Carbon Resources Inc. (CA). Sulfuric acid was purchased from Fisher Scientific Inc. (USA). Sodium hydroxide (60 %wt) was obtained from Ricca Chemical Company (USA) and diluted to 5–30 %wt. for use.
Amine concentration was defined the percentage of corresponding amine by mass balance
%Amine concentration
W amine 100% W amine þ wDiluent
ð1Þ
The concentration of HAC in organic phase was determined by mass balance
½HAorg
eq
½HAaq V aq
initial
¼
½HAaq V aq
eq
ðV org Þaq
ð2Þ
where Vaq is the volume of aqueous phase (mL) and Vorg is the volume of organic phase (mL). For the evaluating extraction efficiencies of different runs, HAC recovery (%) and distribution coefficient (KD) were introduced. The percent weight of HAC transferred from the aqueous phase into organic phase was expressed the percentage recovery of corresponding HAC.
%Recovery ¼
ð½HAorg V org Þaq ð½HAaq V aq Þinitial
100%
ð3Þ
The equilibrium distribution coefficient (KD) was defined the ratio of the HAC weight fraction of organic phase (bHAcorg Vorg ) to that of aqueous phase (bHAcaq Vaq ) , at equilibrium.
KD ¼
½HAorg V org ½HAaq V aq
!
ð4Þ eq
2.2. Activated carbon treatment 2.7. Regeneration of tertiary amine and solvent/diluent The PHL was treated with activated carbon (AC) at room temperature and in sonication for 30 min. The weight ratio of PHL to AC was 20:1. 2.3. Sugar analysis The sugar content of the PHL was determined by using an Ion Chromatography unit equipped with CarboPac TM PA1 column (Dionex-300, Dionex Corporation, USA) and a pulsed amperometric detector (PAD). The details methods are described in elsewhere [16,17]. 2.4. Acetic acid and furfural analysis
The regeneration of amine and solvent/diluent was done by adding aqueous sodium hydroxide in organic phase for 20– 90 min at 1–4 M ratio of sodium hydroxide to HAc and shaking speed 200 rpm. Recovery of HAc by NaOH is based on the concentration of HAc in organic phase (Eq. (2)). The percent weight of HAc transferred from the organic phase into aqueous phase (sodium acetate) was expressed the percentage recovery of corresponding HAc.
½HAaq V aq eq % Recovery ¼ ½HAorg V org
100%
ð5Þ
initial
A Varian 300 NMR–spectrometer was employed for determining the furfural and acetic acid concentrations as methods described earlier [17].
3. Results and discussion
2.5. Lignin analysis
Diluent for tertiary amine plays an important role in the extraction process [9,11,18,19]. Therefore, selection of a suitable diluent is an important factor for extracting acetic acid from the PHL. Fig. 1 shows the extraction equilibrium of acetic acid from the TPHL by TIOA in different diluents at the mole ratio of 1. The degree of extraction of acetic acid with TIOA was in the order of 2-ethyl-1-hexanol (E) > E + 1-octanol (O) > 1-decanol (D) > D + E > D + O > O > E + kerosene (K) > D + K > K. The maximum extraction of 68.79% was obtained for 2-ethyl-1-hexanol while the minimum extraction was 13.36% only for kerosene. The lower extraction equilibrium of kerosene can be increased to 53.13% and 52.92% with the addition of decanol or 2-ethyl-1-hexanol in kerosene, respectively. The above results that polar diluents like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance in recovering acetic acid from the TPHL when extracted using TIOA, than the nonpolar diluent can be explained as follows. The salvation of
The UV/Vis spectrometric method at a wavelength of 205 nm (Tappi UM250) was used to measure the lignin content of PHL [16]. 2.6. Liquid–liquid extraction Required amount of the organic phase (tertiary amine and diluent or solvent) and aqueous solution (AC treated PHL samples) were charged in flasks separately. A extraction was performed by stirring by magnetic bar with heating at 400 rpm or shaking by shaker with heating at 200–300 rpm and varied temperature of 25–50 °C for the varied time of 5–15 min, and pH value of the AC PHL–amine mixture was adjusted by adding NaOH. Then the extraction mixture was centrifuged at 3000 rpm for 5 min to assist separation of organic and aqueous phases. The two phases were analyzed immediately after separation.
3.1. Effect of different diluents for tertiary amine
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Table 2 Effect of time, temperature and pH on the recovery of acetic acid from the activated carbon pre-treated PHL (molar ratio of TIOA/TOA to acetic acid of 1, 30% TIOA dilution). Time (min)
Fig. 1. Effect of different solvents for 30% TIOA concentration on recovery of acetic acid at molar ratio 1 (D – 1-decanol, E – 2-ethyl-1-hexanol, O – 1-octanol, K – Kerosene. For D + K or E + K solvents the weight ratio of D/E to K was 2. For D + E, E + O and D + O system, the weight ratio was 1).
2 4 8 10 12 10 10 10 10 10 10 10 10
Temperature (°C)
25 25 25 25 25 20 25 30 50 25 25 25 25
pH
4.5 (original) 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 5.0 5.5 6.5
Acetic acid recovery (%) TIOA
TOA
66.14 66.18 67.27 67.52 67.46 65.79 67.52 67.16 62.18 67.52 65.12 64.17 61.12
72.26 73.13 73.26 73.32 73.17 70.08 73.32 70.50 66.41 73.32 70.02 66.99 61.02
3.3. Effect of time, temperature and pH the complex by the diluents is one of the most important factors in extraction of carboxylic acid. A polar diluent increases the extracting power of nonpolar amines by providing additional solvating power that allows higher levels of polar acid–amine complexes to stay in the organic phase. Sahin et al. [12] observed that the solubility of acid–amine complex increases as the polarity of diluents increases. Especially, protic halogenated hydrocarbons and alcohol diluents, chloroform and 1-octanol, give an unusually high degree of extraction through the specific hydrogen bonding between the proton of the diluent and the acid–amine complex [20,21].
3.2. Effect of 2-ethyl-1-hexanol as diluent The amounts of TIOA and 2-ethyl-1- hexanol as the diluent, are critical in the extraction process and they need to be optimized. Effects of TIOA concentration and mole ratio on the recovery of acetic acid and distribution coefficient are shown in Table 1. It is seen from the Table 1 that the acetic acid recovery was increased with increasing molar ratio of TIOA, consequently increased equilibrium distribution coefficient KD. For example, at the molar ratio of 1, the acetic acid recovery was 67.4% with the TIOA concentration of 32%, it was 78.4% with the increase of molar ratio to 2 at the same dilution. The TIOA concentration (in 2-ethyl-1-hexanol) had only marginal effect on the extraction of acetic acid. Diluent influenced the formation of acid–amine complexes. And the dipole–dipole interactions between solvent and complex can promote the formation of acid–amine complex by the complex-solvent hydrogen bond [22]. Zhong et al. [23] studied the reactive extraction of propionic acid using alamine in 2-octanol and 1-dodecanol as diluents at various amine concentration (0–100%) and found extraction to be maximized at the amine concentration between of 20–40%. The diluted extractant gave much higher KD values [24]. In the subsequent study, a molar ratio of TIOA to HAc of 1, and the TIOA concentration of 30% were chosen.
The effects of time, temperature and pH on the extraction of acetic acid from the PHL by TIOA or TOA using 2-ethyl-1-hexanol as the diluent, are shown in Table 2. The extraction was carried out with tertiary amine at 30% concentration at 1 M ratio with varying time, temperature and pH and the results. It can be found that the recovery of acetic acid was reached to equilibrium within 10 min and the recovery reached 67% and 73% for TIOA and TOA at 25 °C, respectively. Similarly, a fast acetic acid extraction was observed from the bio-oil by TOA [8]. This fast reaction can be explained by the acid–base reaction during extraction process. A further increase of temperature from 25 to 50 °C, had a negative effect on the extraction efficiency, since the acetic acid recovery was decreased. The reason may be explained by the instability of acetic acid–amine complex and shifting of extraction equilibrium at higher temperature [25,26]. Table 2 also shows that the increase of pH from the initial mixture pH of 4.5 negatively affected the extraction efficiency of acetic acid, which complies with the conclusions of Yang et al. [27]. In summary, it can be concluded that the extraction process of acetic acid from PHL into diluted tertiary amine/2-ethyl-hexanol system can be completed within 10 min, optimal temperature for the recovery of acetic acid was 25 °C. The pH of the system should not increase. 3.4. Regeneration of amine and solvent Regeneration and reuse of amine and solvents/diluents in recovering acetic acid from the PHL would be desirable, and it was carried out by using sodium hydroxide. Sodium hydroxide reacted with acetic acid in HAc–amine complex to form sodium acetate, and subsequently TIOA/TOA and the diluent were regenerated. The regeneration was done by varying molar ratio of sodium hydroxide to HAc from 1 to 4, reaction time from 20 to 90 min and results are shown in Figs. 2 and 3. The acetic acid
Table 1 Effect of TIOA dilution by 2-ethyl-1-hexanol and molar ratio on the recovery of acetic acid from the activated carbon pre-treated PHL (extraction time, temperature and pH were 10 min, 20 °C and 4.5 respectively). Mole ratio/dilution
26 32 36
0.5
1.0
1.5
2.0
Recovery (%)
KD
Recovery (%)
KD
Recovery (%)
KD
Recovery (%)
KD
49.7 52.7 49.4
0.99 1.11 0.98
67.0 67.4 64.9
2.05 2.06 1.86
77.3 75.2 74.2
3.35 3.03 2.87
78.6 78.4 76.1
3.67 3.63 3.19
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time of regenerated solvent. After 4th time recycling of regenerated solvent, the HAc recovery was decreased by 2.55% and 1.54% for TIOA and TOA, respectively (Table 3). This lower recovery efficiency can be overcome by increasing the molar ratio. In the 4th time recycling of regenerated solvent, the recovery of HAc was increased from 63.03% to 66.01% for TIOA and with increasing molar ratio from 1 to 2. The reason for the lower extraction yield when using recycled solvent/diluent, may be due to the existence of a small amount lignin in the organic phase, which can hinder the HAc extraction. 4. Conclusions Fig. 2. Effect of regeneration time on the recovery of HAc (NaOH–HAc molar ratio, 1).
Compared to nonpolar diluent kerosene, polar diluents like 1-decanol, 1-octanol and 2-ethyl-1-hexanol showed better performance in recovering acetic acid from the TPHL when extracted using TIOA. The lower extraction of acetic acid in kerosene can be improved by adding decanol or 2-ethyl-1-hexanol. The extraction process was very fast and its equilibrium was reached within 10 min at 25 °C. A higher pH increased the dissociation of acetic acid, as a result decreased the extraction yield of acetic acid. The molar ratio of NaOH to HAc played an important role in organic phase regeneration process and acetic acid recovery from the organic phase. Acknowledgements
Fig. 3. Effect of NaOH–HAc mole ratio on the recovery of HAc from the loaded organic phase (regeneration time 60 min).
Table 3 Effect of recycling of regenerated solvent and mole ratio on the recovery of HAc from the loaded organic (30% amine concentration at 1 M ratio and regeneration time 60 min). Ratio (mole)
1 1 1 1 1 2 2 2 4
Recycling (times)
1 2 3 4 1 2 3 4 5
HAc recovery (%) TIOA-E
TOA-E
65.58 64.05 63.69 63.03 65.58 66.87 66.37 66.01 67.38
68.48 68.17 67.43 66.94 68.48 71.62 69.75 68.66 72.49
recovery from the loaded organic phase was improved slightly with increasing regeneration time and molar ratio of NaOH to HAc. At the mole ratio of 1, HAc recovery as Na-acetate was increased from 63.01% to 65.58% for TIOA-E system and from 64.69% to 69.48% for TOA-E system with increasing reaction time from 20 min to 60 min, further increase of time did not increase HAc recovery significantly. It also can be seen that HAc recovery was increased from 65.58% to 67.89% for TIOA-E system and 68.48% to 72.69% for TOA-E sytem with the increase of mole ratio from 1 to 4. The effect of molar ratio was pronounced when recycle the regenerated solvent for further recovery of HAc from the loaded organic solvent (Table 3). The effect of recycling the regenerated solvent/ diluent on the HAc recovery of was also studied. As shown in Table 3, the HAc recovery yield was decreased slightly with increasing recycling
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