Green recovery of hazardous acetonitrile from high-salt chemical wastewater by pervaporation

Green recovery of hazardous acetonitrile from high-salt chemical wastewater by pervaporation

Journal of Cleaner Production 197 (2018) 742e749 Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsev...

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Journal of Cleaner Production 197 (2018) 742e749

Contents lists available at ScienceDirect

Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Green recovery of hazardous acetonitrile from high-salt chemical wastewater by pervaporation Yong Wang a, *, Xiang Mei b, Tengfei Ma c, Changjing Xue b, Meidan Wu a, Min Ji c, Yuegang Li c a b c

State Key Laboratory of Pollution Control and Resource Reuse, School of the Environmental, Nanjing University, Nanjing, 210023, China College of Biology and the Environmental, Nanjing Forestry University, Nanjing, 210037, China Deptartment of R&D, SinoChem TaiCang Chemical Industrial Park, TaiCang, 215433, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 21 January 2018 Received in revised form 20 June 2018 Accepted 22 June 2018 Available online 26 June 2018

Acetonitrile in high-salt wastewater is not only a pollutant and a toxic and hazardous problem but also an inefficient use of resources. Acetonitrile in high-salt wastewater is refractory to and difficult for wastewater treatment. In this work, the separation and recovery of hazardous acetonitrile from high-salt aqueous streams by pervaporation were investigated, and the operating process conditions were evaluated. The separation of acetonitrile from wastewater was conducted using a polydimethylsiloxane (PDMS) membrane and was promoted by high concentrations of acetonitrile and high temperatures. The activation energy for the permeation of acetonitrile and water through the membrane indicated that the pervaporation of acetonitrile is more highly temperature dependent than that of water. The maximum permeate flux achieved was 353 g/m2h, and the highest concentrations of acetonitrile in the permeate were found to be greater than 47%. The results also showed that high salt in wastewater had a positive effect on the pervaporation performance and the separation factor. The process provides a paradigm change toward viewing the acetonitrile in wastewater as a resource to be recovered rather than waste to be treated, and thus, clean production can be realized. © 2018 Elsevier Ltd. All rights reserved.

^ as de Handling Editor: Cecilia Maria Villas Bo Almeida Keywords: Chemical industry Pervaporation Recovery Acetonitrile High-salt wastewater

1. Introduction Acetonitrile is used as a solvent in the fine chemicals industry and the manufacture of pharmaceuticals, including C6fluoroketone, vitamin A, cortisone and carbon amine drugs. Acetonitrile is also commonly used as a moderately active solvent in the organic synthesis of many typical nitrogen-containing chemical substances, including thiamine and amino acids. The release of acetonitrile into aquatic media is of particular concern since it may be a moderately toxic substance to human beings and can be converted into hydrogen cyanide and acetaldehyde in living organisms (C. Li et al., 2016). Acetonitrile containing wastewater is toxic organic industrial sewage which needs treatment to make it harmless. Furthermore, the presence of acetonitrile in chemical effluents implies that valuable materials are leaking out of economic systems. Acetonitrile, as a volatile organic compound (VOC), is infinitely

* Corresponding author. E-mail address: [email protected] (Y. Wang). https://doi.org/10.1016/j.jclepro.2018.06.239 0959-6526/© 2018 Elsevier Ltd. All rights reserved.

miscible with water and hazardous when discharged into chemical wastewater. Thus, it is required that innovative, cost-effective technology be developed for acetonitrile wastewater treatment. In recent years, biofilm treatment (C. Li et al., 2016; T. Li and Liu, 2008), electrolysis and Fenton oxidation have been used for the degradation of acetonitrile in wastewater. A recombinant bacterium, strain B. subtilis N4-pHT01-nit, with biofilm formation and nitrile degradation functions can help degrade acetonitrile in water treatment (C. Li et al., 2016). However, these technologies cannot recover valuable acetonitrile and always necessitate the addition of other reagents, which increase the treatment expenses, thus preventing these technologies from meeting the demands of clean production. Organophilic pervaporation is a process for removing organics from aqueous solutions to yield an organic concentrate that can be treated for reuse. When the organics/water mixture flows through one side of the membrane, the organics are absorbed and permeated through the membrane driven by a vacuum, and then they are evaporated into the vapour and condensed on the other side of the membrane. The treatment process is promising because it has the

Y. Wang et al. / Journal of Cleaner Production 197 (2018) 742e749

merits of a small footprint, energy efficiency, environmental benignity and effective recovery of volatile organic components. There is also no emission problems, and it is easy for pervaporation treatment facilities to operate. Pervaporation can be a solution when the organics in the wastewater need to be recovered for their value or when other treatment technologies do work well. Organophilic pervaporation is expected to become a clean technology for the recovery of acetonitrile from high-salt chemical wastewater. A significant amount of work has been done on VOC wastewater treatment. Because hydrophobic PDMS does not allow water molecules to pass through easily, the water contact angle is much higher (>100 ) than that of organics (Ramaiah et al., 2013). PDMS has high selectivity and permeability for volatile organic molecules (Liu and Xiao, 2004). The removal of VOCs such as benzene, chloroform and toluene from organics/water mixture using PDMS membranes (Ohshima et al., 2005)and polystyrene-bPolydimethylsiloxane (PSt-b-PDMS) membranes by pervaporation has been investigated (Uragami et al., 2016). The pervaporation of styrene/water (Aliabadi et al., 2012) and n-butanol/water mixtures by ceramic-supported PDMS membranes (Dong et al., 2014) also was studied. García et al. studied the separation of n-butanol/ dichloromethane/water mixtures by pervaporation in the presence of sodium chloride (García et al., 2009; García et al., 2013). The extraction of volatile chlorinated hydrocarbons from aqueous solutions was studied using hydrophobic mixed matrix membranes of PDMS supported on a polyvinyldinefluoride (PVDF) substrate (Ramaiah et al., 2013). Santoro et al. revealed that membranes with a PDMS intermediate layer can improve the EtOH/H2O selectivity in comparison to a pure flat SBS membrane (Santoro et al., 2017). Hao et al. studied phenol removal from water using poly (ether-blockamide) (PEBA 2533) membranes (Hao et al., 2009). The removal of acetone, acetonitrile and ethanol from water by pervaporation was investigated by Khayet. The organic selectivity was found to be in the order of acetone > acetonitrile > ethanol (Khayet et al., 2008). GAO studied the separation of 1-butanol/water mixtures (5%) by PV using the PIM-1/PVDF thin-film composite membrane and found that the total flux can reach 9 kgm2 h1 with separation factors up to 18.5 (Gao et al., 2017). A mass transfer mathematical model has been developed, and the transfer rate of organics across the TFC membrane was measured in pervaporation using feed solutions with different NaCl concentrations (Cocchini et al., 2002a, 2002b). The pervaporative removal of VOCs such as acetone (Zhang et al., 2016), chloroform (Urtiaga et al., 1999), toluene (Chovau et al., 2010), styrene ethyl benzene (Yahaya, 2008), xylene (Jian et al., 1996), hazardous organic solvents (MTBE, EtAc and BuOH) (Kujawa et al., 2015), and methanol (Yi and Wan, 2017) from solvent/water mixtures was also investigated. However, the recovery of acetonitrile from high-salt organic wastewater has not been studied. In this work, the pervaporation process for treating the volatile organic compound (VOC) acetonitrile in chemical wastewater at different feed concentrations, temperatures and salinities was evaluated. The wastewater contained acetonitrile with a concentration of 3000~40000 mg/L in a high salinity of approximately 20% sodium chloride. The pervaporative removal of acetonitrile from wastewater and acetonitrile concentrates is conducted in this paper. The condensed acetonitrile can be treated for reuse. 2. Materials and methods 2.1. Materials The hydrophobic ceramic membranes with a functional PDMS layer used in the experiments were provided by Nanjing JiuSi Corporation (Nanjing, China). Acetonitrile (HPLC grade, purity 99.9%) and sodium chloride (reagent grade, purity 99.8%) were

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supplied by Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). 2.2. Wastewater quality Wastewater containing the acetonitrile generated from C6fluoroketone production was collected from SinoChem Environmental Protection Chemicals Corporation in TaiCang, China. Since C6-fluoroketone is a new product in China, there are no data about the wastewater from the literature. The Government required the project's environmental protection facilities and the product's production projects to be constructed and put into production at the same time. Therefore, we carried out the research on the treatment of this wastewater when the product was in the pilot stage. The characterization of the wastewater was performed to determine the composition and evaluate the potential for pervaporation separation. The effluents were analysed for COD, BOD, total nitrogen (TN), and total dissolved solids (TDS) according to standard methods. The sample concentrations of acetonitrile were determined by gas chromatography (HP6890). The concentrations of sodium ions and chloride ions were analysed by ion chromatography (Thermo Scientific Dionex ICS 5000). The typical wastewater characteristics are listed in Table 1: 2.3. Pervaporation tests Pervaporation tests were performed with a lab-scale system schematized in Fig. 1. It consisted of a feed tank, a peristaltic pump, a ceramic membrane module, a cold trap and a vacuum pump. The ceramic PDMS membrane module (JiuSiCorp., Nanjing, Jiangsu, China) has a membrane area of 303 cm2. The liquid solution was recirculated through the membrane module at a speed of 0.5 L/min, and the temperature of the solution was kept constant at 40  C by using a water bath. The aim of recirculation is to maintain a constant concentration and temperature of the feed solution in the pervaporation cell. During the experiments, a permeate pressure of 4e15 mbar (2XZ-2 Huanyan Tianlong Vacuum Inc., China) was applied to the system by a vacuum pump. The cold trap was immersed in a liquid nitrogen bath to collect the acetonitrile-rich permeate for analysis. Wastewaters containing low concentrations of acetonitrile were treated by pervaporation. For each set of experiments, the operating parameter was varied one at a time and covered the following ranges: feed concentration of 0.1~4 wt% acetonitrile and operating temperature of 18~55  C. The collected permeate sample was weighed and analysed every hour. 2.4. Swelling experiment The gravimetric method was used to determine the swelling degree of the PDMS/ceramic composite membrane. The membrane dry weight was first determined using an electrical balance (model AR522CN,OHAUS, ShangHai,China). The dry membrane was immersed in a container filled with acetonitrile wastewater at room temperature of 20  C.After a fixed time interval, the free liquid on the surface of the swollen membrane was wiped out carefully by using tissue paper before weighting. The degree of swelling of the membrane, S, was determined by



Ws  Wd Ws

(1)

where ws and wd represent the weight of the dry and swollen membranes, respectively.

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Table 1 Typical physical and chemical characteristics of wastewater collected from the factory. pH

COD (mg/L)

BOD (mg/L)

TN (mg/L)

TDS (mg/L)

Naþ (mg/L)

Cl (mg/L)

Acetonitrile (mg/L)

4.92

35012

2840

6498

220000

72727

125683

18256

  Ea J ¼ J0 exp  Rg T

(4)

where J is the permeate flux (kgm2h1), Ea is the activation energy (J/mol) associated with the permeate process, Rg is the gas constant (J/mol K) and T is the absolute feed temperature (K). 3. Results and discussion 3.1. The physical/chemical properties of acetonitrile and water are listed in Table 2

Fig. 1. Pervaporation experiment setup.

2.5. Measurement of water contact angle The contact angle of water sessile drops at the surface the PDMS networks was measured on JC2000D contact angle apparatus (Shanghai ZhongChen Digital Technology Apparatus Co. Ltd) at room temperature. The volume of the water drop was 5 ml for each test. At least five measurements were performed for PDMS membrane and the average value calculated.

2.6. Analytical facilities The acetonitrile concentrations in the collected samples were determined by gas chromatography (HP 6890, automatic headspace sampler) equipped with a flame ionization detector (FID). The mobile phase flow rate was kept at 1 ml/min and the detector temperature was kept at 250  C.

The membrane performance can usually be determined from the permeation flux (J) and the separation factor (a). The membrane flux of acetonitrile and water is given as a mass flux:

(2)

where Ji is the mass permeation flux (g/m2h), mi is the weight of the permeate (g), Am is the effective membrane area (m2), and t is the permeation time (h). The separation factor of the membrane, a, is defined as below:



y2 =y1 x2 =x1

The degree of membrane swelling is an important factor in PV process. The swelling behaviour of the PDMS/ceramic membrane in acetonitrile wastewater is showed in Fig. 2. The swelling degree of the PDMS/ceramic membrane is around 6.6%.Since the porous ceramic support is inert to organic liquids, the swelling of the PDMS/ceramic composite membrane is low. Our results confirmed that the swelling of the PDMS membrane is suppressed by the ceramic support (Wei et al., 2011). The result obtained from the investigation offer the information to explain the well performance of PDMS/ceramic composite membrane in pervaporation process. The hydrophobic property was significant for the pervaporation separation. The water contact angles of PDMS membrane were measured. As shown in Fig. 3, it was found that the contact angle of PDMS membrane was about 123.4 , which demonstrates that PDMS membrane has good hydrophobicity. 3.3. Performance of the PDMS/ceramic composite membrane

2.7. Calculated quantities

m Ji ¼ i Am t

3.2. Swelling behaviour and hydrophobic property of PDMS/ceramic composite membrane

(3)

where x2 and x1 are the respective mass fractions of acetonitrile and water in the feed and y2 and y1 are the respective mass fractions of acetonitrile and water in the condensed stream. The temperature relation of the permeate flux is expressed by the following Arrhenius-type equation.

To investigate the effects of the working conditions on the PV performance of acetonitrile wastewater, the pervaporation experiments were conducted using filtered acetonitrile wastewater. 3.3.1. Effects of concentration on PV performance The acetonitrile concentration in the feed solution can influence the mass transfer rate significantly. We studied a wide range of concentrations since there was a fluctuation in the composition of the wastewater when the product was in the pilot stage. The experiments were performed at a constant temperature with the acetonitrile concentrations ranging from 0.3~3.6%. Fig. 4 shows that the permeate acetonitrile concentration increased with increasing feed acetonitrile concentration. When the concentration of acetonitrile in the feed wastewater is approximately 3.6 wt%, the concentration of acetonitrile in the permeate can reach 47 wt%. Compared with the acetonitrile pervaporation in literature (Khayet et al., 2008), it must be pointed out that the concentration of acetonitrile in the permeate increases with the concentration in feed wastewater in the studied range. Fig. 5 and Fig. 6 show the effects of the acetonitrile concentration on the partial flux and selectivity through the membrane. The

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Table 2 Physical and chemical properties of acetonitrile and water. Component Acetonitrile Water

Molecular Weight (g/mol)

Molar Volume (106 m3/mol)

Boiling point ( C)

Vapour pressure (pa at 20  C)

41.05 18.02

52.4 18.0

82 100

9540 2340

Fig. 2. Swelling behaviour of PDMS/ceramic composite membrane versus immersion time (test with feed of 1.6% acetonitrile wastewater at 25  C).

D(solubility parameter) (103J1/2/m2/3)

24.1~24.5 47.9~48.1

Fig. 4. Acetonitrile concentration in the permeate versus the acetonitrile concentration in the feed solutions (V ¼ 350 ml, temperature of 40  C).

Fig. 3. Water contact angle of PDMS membrane.

original acetonitrile concentration ranged from 0.3~3.6%, and the concentrations in the permeate were in the range of 7~47%. The partial acetonitrile and water fluxes were calculated and are shown in Fig. 5. The permeation of the total flux and the acetonitrile partial flux were found to increase with the feed concentration. The acetonitrile flux increased linearly since the increase in the concentration in the feed wastewater increased the driving force of acetonitrile through the membrane. However, the water flux showed a trend of first rising and then falling. This result may be explained by the fact that the water molecules clustered due to the hydrogen bonding between water molecules, which will reduce their diffusivity and permeability. Furthermore, the selectivity for acetonitrile was estimated, and the results are shown in Fig. 4. From the physical properties of the acetonitrile listed in Table 2, acetonitrile has a lower solubility parameter and a greater size than water. The PDMS membrane may have a solubility parameter close to that of acetonitrile. The acetonitrile selectivity of the membrane remained a constant around 25, indicating the membrane is very effective for acetonitrile removal and recovery from wastewater by

Fig. 5. Permeate flux versus acetonitrile concentration in feed wastewater (V ¼ 350 ml, 40  C).

pervaporation even at higher acetonitrile concentrations. The trend of acetonitrile flux and total flux is similar to the literature and the acetonitrile selectivity achieved is better than that in the reported literature (Khayet et al., 2008). The acetonitrile selectivity results confirmed that the separation factor decreased with the feed concentration that reported in the literature (Khayet et al., 2008).

3.3.2. Effect of circulation flow rate on PV properties The effect of the circulation flow rate on PV properties at an acetonitrile concentration of 11573 ppm is shown in Fig. 7. The total flux and the acetonitrile partial flux were found to increase with the feed flow rate. The Reynolds number, Re, was calculated from Eq. (5):

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and the total flux.

Fig. 6. Acetonitrile selectivity versus acetonitrile concentration in the feed (35  C).

3.3.3. Effects of feed temperature on PV properties At a given feed acetonitrile concentration of 16852 mg/L, the influence of various temperatures on PV properties was studied in the range of 291~328 K (18~55  C). Fig. 8 shows the effects of the temperature on the acetonitrile concentration in the permeate. It can be seen that the acetonitrile concentration in the permeate decreases as the temperature increases. This decrease in the acetonitrile concentration in the permeate may be attributed to the rapid increase of water vapour permeation through the membrane. The permeate fluxes are plotted as a function of the feed temperature in Fig. 9. The permeate fluxes could be observed to increase exponentially with the temperature. The total fluxes were from the experiment, while the partial acetonitrile and water fluxes were calculated. The acetonitrile selectivities are plotted as a function of the temperature in Fig. 10. A significant decrease in the separation factors was observed with increasing temperature. In pervaporation, the molecules permeate through the free volumes produced by the random thermal motion of the polymer chain. The amplitude and the frequency of the polymer chain movement increase with temperature. The increase in the free volume in the membrane provides more space for the molecules to diffuse, which produces a higher permeate flux. However, a membrane with larger free volumes may have a lower separation capability, thus resulting in a lower acetonitrile separation selectivity, as shown in Fig. 10. The results are consistent with the previous PV performance in literature (Aliabadi et al., 2012; Dong et al., 2014). The permeation rate can be described as a thermally activated process that obeys the following Arrhenius-type relationship:

  Ea J ¼ J0 exp  Rg T

Fig. 7. The effect of Reynolds number on the fluxes at an acetonitrile feed concentration of 11573 mg/L, (V ¼ 350 ml, 40  C).

Re ¼

dh ur

m

It is observed that the temperature dependence of the total permeation flux and the partial permeation of acetonitrile and water fluxes should obey an Arrhenius type of relation, as shown in Fig. 11, which is consistent with the previous literature (Yi and Wan, 2017). As the feed temperature rises, the acetonitrile and the water molecules become more energetic, the thermal motion of the polymer chains is stimulated, and the saturated vapour pressure on

(5)

where dh is the hydraulic diameter of the pervaporation cell, u is the feed velocity on the surface of membrane, r is the density and m is the viscosity of the feed. Fig. 7 shows that with the increase of the Reynolds number, the total permeate flux and acetonitrile partial flux initially increased and then decreased. When the Re number for the PDMS membrane is raised from 281 to 555, the acetonitrile flux changes from 43.7 to 67.5 gm2 h1, and the total flux increased from 235 to 315 g m2h1. After that, the acetonitrile flux decreases from 67.5 to 47.5 gm2 h1 when the Re number is raised from 555 to 1250, and the total flux also decreases gradually. It is known that an increase of the flow rate could reduce the effect of concentration polarization, thus increase the organic permeation flux, as literature reported (Aliabadi et al., 2012). The liquidmembrane boundary tends to be thinner with increasing Reynolds number, which improves the mass transfer and tends to improve the permeate flux. However, our results suggest that the high salt concentration impedes the increase in the acetonitrile flux

(6)

Fig. 8. Permeate acetonitrile concentration versus temperature.

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the feed side increases. The aspects described above will make the permeation easier and increase the partial flux of both acetonitrile and water. The activation energies can be obtained from the semilogarithmic plots of the permeate fluxes against the reciprocal of the absolute temperature (1/T), as shown in Fig. 11. Fig. 11 shows that the results agree with the Arrhenius type of relation. The equations found for the fluxes against the reciprocal of the absolute temperature (1/T) using the data in Fig. 11 are given as follows:

JAce ¼ 0:02423 e2061=T JWater ¼ 0:002091 e883=T JTotal ¼ 0:005628 e1118=T

Fig. 9. The effect of the operating temperature on the acetonitrile, water and total fluxes obtained at full vacuum for a feed concentration of 16852 mg/L and V ¼ 350 ml.

Fig. 10. Acetonitrile selectivity versus feed temperature (V ¼ 350 ml).

where JTotal (kg m2 s1)¼(acetonitrile þ water) flux, JWater (kg m2 s1) ¼ water flux, and JAce (kg m2 s1) ¼ acetonitrile flux. The values of the overall activation energy and the partial activation energies of acetonitrile and water were obtained and are listed in Table 3. The pervaporation partial activation energies were calculated from the slope of the figure and were found to be 17.13 and 7.34 kJ/ mol for the acetonitrile and water fluxes, respectively. The activation energy for acetonitrile permeation is higher than that for water permeation. This result implies that the behaviour of the acetonitrile permeation is more sensitive towards temperature changes than that of the water permeation. The differences in the permeate activation energy for acetonitrile and water may arise from several factors. Since the acetonitrile molecular size is about three times larger than that of water, the acetonitrile activation energy is higher than that for water. The activation energies of our results is lower than the acetonitrile and water activation energies in the literature (Khayet et al., 2008). The affinity between the permeate molecules and the PDMS membrane and the interactions between the acetonitrile and water molecules in the salt solution may have effects. The pervaporation flux increases with temperature, but selectivity usually decreases with temperature. The acetonitrile separation factor was calculated by Eq. (2) and showed a decrease in selectivity when the temperature was raised from 18  C to 55  C in Fig. 12 because the free volume in the membrane increased and water molecules become freer. As a result, the interaction between water molecules weakened, and water molecules were smaller in size and permeated more easily.

3.3.4. Effects of salt concentration on PV performance The solubility of an organic compound decreasing in a salt solution is called the salting-out effect. The salt may have a positive influence on the PV performance through the salting-out effect, but the salt may cause an increase in the density and viscosity of the feed, thereby decreasing the mass transfer rate and resulting in a negative effect (García et al., 2013). Salts of organic cations can increase the solubilities, which is known as the salting-in effect and reduces the pervaporation driving force (García et al., 2013). The effects of the salt concentration on the permeation flux and acetonitrile concentration decreases over time were investigated

Table 3 Values of the permeate activation energy, Ea, of the total and partial permeate fluxes. Fig. 11. The effect of the reciprocal of the temperature on the semi-logarithmic plots of the acetonitrile partial flux, the water partial flux and the total permeate flux.

Ea (KJ/mol)

Acetonitrile flux

Water flux

Total flux

17.13

7.34

9.287

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Y. Wang et al. / Journal of Cleaner Production 197 (2018) 742e749 Table 4 Pervaporation of the original wastewater containing acetonitrile and salt. Item/Acetonitrile wastewater

1

2

3

Acetonitrile concentration (ppm) Permeation flux (g/m2h) Acetonitrile Water Total flux Permeate concentration (ppm) Acetonitrile Selectivity (a)

5913

12327

17728

31.56 152.25 183.8 171696 28.21

67.494 247.99 315.48 213940 21.8

113.30 238.81 352.11 269210 24.92

wastewater treatment. 4. Conclusions

Fig. 12. Permeate flux versus salt concentration in feed wastewater (V ¼ 350 ml, 40  C).

for the pervaporation of acetonitrile wastewater at 40  C. Although the concentration of wastewaster samples we collected from the pilot test is about 20%, there was assumption that the salt concentration of samples can be varied and we were interested in the effect of the salt concentration on the PV performance. We took 5% as the lower limit is that the wastewater can be biodegradable when the salt concentration is below 5% so the pervaporation is not needed. Wastewaters with salt concentrations varied from 5% to 20% were made by diluting the wastewater and then adding pure acetonitrile to the wastewater to maintain the same feed concentration. The effects of the salt concentration on the performance are illustrated in Fig. 12. Both the total flux and partial water flux showed a slow increasing trend with the increase in the salt concentration in the wastewater, but the separation factor shows an upward trend after the salt concentration increased to more than 10%. A salt concentration of 20% in wastewater will help decrease the permeate flux and increase the separation factor significantly, which is different from the modest effect of a salt concentration below 1% observed in the literature (García et al., 2009). First, this may be due to the electrostatic interactions between the water and sodium chloride molecules, where the interactions promote the ionic salt to form hydration shells, which reduces the amount free water to dissolve the acetonitrile molecules. Therefore, the water flux and the solubility of acetonitrile decrease significantly in highsalt wastewater. Second, the high salt concentration in wastewater increases the activity coefficient and enhances the PV driving force. Third, a 20% concentration of salt results in a greater density of wastewater and the accumulation of acetonitrile on the surface of the brine solution. In other words, the acetonitrile will float on the solution. Therefore, the increase in salt concentration caused the increase in selectivity for acetonitrile. Fig. 12 illustrates the above mentioned results. 3.4. Pervaporation of wastewater The pervaporation of acetonitrile wastewater was performed at a temperature of 40  C. The results are shown in Table 4. The membrane is highly selective for acetonitrile. When the acetonitrile concentrations in wastewater were increased, the total fluxes and partial acetonitrile fluxes were increased. The separation factor was greater than 20, which indicates that pervaporation holds promise for acetonitrile

The recovery of acetonitrile from chemical wastewater using a composite ceramic PDMS membrane was investigated. The membranes were acetonitrile selective with a separation factor more than 20 and a permeate flux of 353 g m2 h1. The results of the experiments showed that the 20% high salt concentration helped decrease the permeate flux and increase the separation factor significantly, which is different from the modest effect of low salt concentrations reported in the literature. With an increase in the feed acetonitrile concentration, the acetonitrile concentration in the permeate increased and reached 47%. The activation energies of pervaporation were 17.13 kJ/mol for acetonitrile and 7.34 kJ/mol for water. The optimal operating conditions suggested for industrial operations are 40  C and a Reynolds number of approximately 500. The acetonitrile selectivity is better than that reported the literature. Finally, to commercialize this technology, future work will study the pilot scale treatment performance. Acknowledgements This work was supported by the Sinochem Environmental Protection Chemicals (TaiCang) Corporation Ltd under the project “Treatment of acetonitrile in high-salt wastewater”, and the Industry-University Research Cooperation Fund from the Jiangsu Province in China (grant number BY2016075-03). Special thanks are given to Prof. Tai-Shung Chung in the National University of Singapore for his kind and valuable help. The authors would like to thank Nanjing JiuSi Membrane Technology Corp. (Nanjing, P.R. China) for supplying the PDMS membranes. References Aliabadi, M., Aroujalian, A., Raisi, A., 2012. Removal of styrene from petrochemical wastewater using pervaporation process. Desalination 284, 116e121. https:// doi.org/10.1016/j.desal.2011.08.044. Chovau, S., Dobrak, A., Figoli, A., Galiano, F., Simone, S., Drioli, E., …, Van der Bruggen, B., 2010. Pervaporation performance of unfilled and filled PDMS membranes and novel SBS membranes for the removal of toluene from diluted aqueous solutions. Chem. Eng. J. 159 (1e3), 37e46. https://doi.org/10.1016/j.cej. 2010.02.020. Cocchini, U., Nicolella, C., Livingston, A.G., 2002a. Countercurrent transport of organic and water molecules through thin film composite membranes in aqueous e aqueous extractive membrane processes. Part II : theoretical analysis. Chem. Eng. Sci. 57, 4461e4473. Cocchini, U., Nicolella, C., Livingston, A.G., 2002b. Countercurrent transport of organic and water molecules through thin ÿlm composite membranes in aqueous e aqueous extractive membrane processes. Part II : theoretical analysis. Chem. Eng. Sci. 57, 4461e4473. Dong, Z., Liu, G., Liu, S., Liu, Z., Jin, W., 2014. High performance ceramic hollow fiber supported PDMS composite pervaporation membrane for bio-butanol recovery. J. Membr. Sci. 450, 38e47. https://doi.org/10.1016/j.memsci.2013.08.039. Gao, L., Alberto, M., Gorgojo, P., Szekely, G., Budd, P.M., 2017. High-flux PIM-1/PVDF thin film composite membranes for 1-butanol/water pervaporation. J. Membr. Sci. 529 (February), 207e214. https://doi.org/10.1016/j.memsci.2017.02.008. cz, E., Muurinen, E., Keiski, R.L., 2009. Recovery of n-butanol from García, V., Pongra salt containing solutions by pervaporation. Desalination 241 (1e3), 201e211.

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