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Efficient and Cost Effective Way for the Conversion of Potassium Nitrate from Potassium Chloride Using Electrodialysis Prem P. Sharma,†,‡ Swati Gahlot,† Abhishek Rajput,† Rajesh Patidar,† and Vaibhav Kulshrestha*,†,‡ †

CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of Scientific & Industrial Research (CSIR),Gijubhai, Badheka Marg, Bhavnagar-364 002, Gujarat, India ‡ Academy of Scientific and Innovative Research, CSIR-Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), Council of Scientific & Industrial Research (CSIR), Gijubhai Badheka Marg, Bhavnagar-364 002, Gujarat, India S Supporting Information *

ABSTRACT: A metathesis electrodialysis (MED) system for the conversion of potassium nitrate from potassium chloride is developed. The experiments are carried out in recirculation mode using a four compartment electro-conversion unit of 200 cm2 effective membrane area with 10 cell pairs. The cation exchange membrane and anion exchange membrane used for the present study are converted from a styrene divinylbenzene based interpolymer film by sulfonation and chloromethylation followed by amination, respectively. Membranes are characterized by means of chemical, mechanical, and thermal properties. Membranes show excellent electrochemical properties with adequate thermal and mechanical stability. About 97% conversion of potassium nitrate is achieved during the sets of experiments with high product purity (99%). Four different applied potentials (1.5, 2, 2.5, and 3 V/cell pair) are used during different sets of experiments in metathesis electrodialysis, out of which 2 V/cell pair is found to be more efficient potential with lower energy consumption of 0.82 kwh·kg−1 for the production of potassium nitrate with 83% current efficiency. KEYWORDS: Metathesis electrodialysis (MED), Ion exchange membranes, Potassium nitrate, Mechanical stability



INTRODUCTION Potassium nitrate is a soluble source of two nutrients and commonly used as a fertilizer for crops that benefit from nitrate nutrition and potassium that is free of chloride.1 Use of KNO3 is especially desirable in conditions where a highly soluble and chloride-free potassium is required. All of the nitrogen is immediately available for plant uptake as nitrate, requiring no additional action and transformation in the soil. About 1,000,000 tons of KNO3 is produced annually, which is used as a fertilizer. Potassium nitrate fertilizer is typically made by reacting potassium chloride with a nitrate source.2−7 Nitrate comes from sodium nitrate, nitric acid, or ammonium nitrate as per the availability and requirements. In industries, the production of KNO3 is based on the reaction of KCl with HNO3 in the presence of pentanol.8 KNO3 crystallizes in the reaction vessel and is removed from the mixture of HCl and HNO3. HCl and HNO3 are recycled back to the reaction. Some other ways are also available for the production KNO3.9−14 © 2016 American Chemical Society

Reaction of ammonium nitrate with potassium hydroxide also produces KNO3. An alternative way of producing KNO3 without a byproduct of ammonia is to combine ammonium nitrate and potassium chloride, easily obtained as a sodium-free salt substitute. KNO3 can also be produced by neutralizing nitric acid with potassium hydroxide, but this reaction is highly exothermic. KNO3 is produced by the reaction of potassium chloride with sodium nitrate by two main synthesis methods. One is the conversion in a reactor by heating; the disadvantages of this method are low yield of conversion and formation of sediments on the surface of the reactor and corrosion. Another method is the exchange of cations in a column with a cationexchanger.15,16 After the exchange of ions, a solution is obtained, and to get a solid product, evaporation and Received: February 3, 2016 Revised: April 6, 2016 Published: April 12, 2016 3220

DOI: 10.1021/acssuschemeng.6b00248 ACS Sustainable Chem. Eng. 2016, 4, 3220−3227

Research Article

ACS Sustainable Chemistry & Engineering Scheme 1. Process Flowchart for the Preparation of Ion Exchange Membranes

without any further purification. Double distilled water was used in all of the experiments. Synthesis of Ion Exchange Membranes. The heterogeneous type interpolymer ion-exchange membranes used in these investigations are prepared.21−23 The interpolymer is prepared by free radical polymerization of styrene, DVB in the presence of xylene as solvent at 100 °C, by a reactive melt-process method. Styrene is added into the molten mixture of polyethylene (PE) in the presence of DVB and BPO, and polymerization is allowed to carry out for 3−4 h at the same temperature. A blow-film extruder is used to convert the polymer into a film of thickness 150−200 μm. Functionalization of the films to convert it into a cation exchange membrane (CEM) was carried out using the standard method of sulfonation using chlorosulfonic acid solution in dichloroethane (DCE) (20:80 v/v). For conversion of the film to an anion exchange membrane (AEM), quaternary ammonium as a functional group is added to the films by chloromethyl methyl ether (CME) in dichloroethane (DCE) (20:80 v/v). The process flowchart for the preparation of membranes is shown in Scheme 1. The membranes were conditioned by treatment with 0.1 M HC1 and 0.1 M NaOH successively and then thoroughly washed with distilled water before their use in MED. Chemical, Structural, and Mechanical Characterization. The samples have been characterized by means of chemical and structural properties. The thermal and mechanical behavior of the membranes are studied using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and universal testing machine (UTM) analysis; details of the characterization are included in the Supporting Information (SI). Physiochemical Characterization. Water uptake behavior of dry membranes is determined by recording the weight gain after equilibrating in water for 24 h. Ion exchange capacity (IEC) of membranes is estimated by the acid base titration. Ionic conductivity of the membranes is measured by a two probe method using a CHI608 potentiostat. Details of the experiments are presented in SI. Counter ion transport numbers of the membranes are calculated by membrane potential using following equation as reported elsewhere.21

crystallization are followed. The disadvantage of this method is obtaining a KNO3 solution of low concentration with higher evaporation cost. Electrochemical production of KNO3 using a cation-exchange membrane has also been performed in the early eighties.17 An alkali metal carbonate substantially free of alkali metal chloride is efficiently produced by electrolyzing an alkali metal chloride in an electrolytic cell having anolyte and catholyte compartments separated by a cation-exchange membrane.18 In electrodialysis lies a double replacement reaction, which can minimize the drawbacks of other processes. Synthesis of potassium nitrate by electrodialysis was performed by Jaroszek et al. using potassium sulfate and sodium nitrate. They obtained 99% purity with high current efficiency.19 Earlier, our group produced potassium carbonate by metathesis electrodialysis (MED) using sodium carbonate and potassium sulfate solution and under optimized conditions; 98% pure potassium carbonate was obtained.20 By the same method, we are trying to achieve the conversion of potassium chloride into potassium nitrate employing low cost and higher purity at medium scale. In this process, exchange of ions takes place between potassium chloride and sodium nitrate separated by an ion exchange membrane in an applied electric field. Earlier, commercially available ion exchange membranes were used for such applications, but those membranes are not chemically and mechanically stable and are very expensive. Here, we tried to explore the potential of indigenously prepared ion exchange membranes for the MED process. The present article investigates the effects of the processing parameters of the MED process for the conversion of potassium nitrate from potassium chloride. A medium sized electrodialysis cell is used with 10 cell pairs of interpolymer based ion exchange membranes for the experiments.



E=

EXPERIMENTAL SECTION

Materials. Styrene (St), p-divinylbenzene (DVB), chlorosulfonic acid (CSA), benzoyl peroxide (BPO), KCl, NaNO3, etc. of AR grade were obtained from SD Fine Chemicals, India. All chemicals were used

RT (2t − 1) γ1C1 In F γ2C 2

(1)

where R is the gas constant, F is the Faraday constant, t is the counterion transport number of corresponding membrane, T is the absolute temperature (298 K), and γ1 and γ2 are the activity 3221

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Figure 1. Schematic representation of the production of KNO3 by a MED process. coefficients at the concentrations C1 (0.1 M) and C2 (0.01 M), respectively, of electrolyte solutions (NaCl) in the testing cell. MED Process for the Conversion of KCl to KNO3. An in-house prepared medium sized electrodialysis (ED) system is used for the experiments with interpolymer CEM and AEM. The schematic diagram of the MED system is presented in Figure 1. The effective area of the membranes used for the experiments is 200 cm2 with 10 cell pairs. The parallel-cum-series flow arrangement is used to monitor each flow stream in respective compartments.20 A four compartment electro-conversion unit is used for the present experiments with two diluted and two concentrated compartments and an electrode wash as per Figure 1. Peristaltic pumps are used to feed the solutions (1000 cm3) in a recirculation mode into the respective compartments with a constant flow rate (0.06 m3 h−1) to maintain the turbulence at 25 °C temperature. A dc power supply was used to apply constant potential across the electrodes, and the resulting current variation was recorded as a function of time. Change in conductivities, concentration of ions, and pH of all of the compartment output are regularly monitored by placing the conductivity and pH electrodes in the respective containers during all of the experiments. The change in concentration of all of the compartments is recorded periodically after 15 min. The i−v curve of CEM and AEM in the MED process is also recorded in equilibration with 0.10 M KCl solution by varying the applied potential from 0 to 5 V/cell pair with the interval of 0.5 V. The energy consumption and current efficiency (CE) are important parameters for any electrochemical process to assess the suitability of the process. The specific energy consumption (P (kWh kg−1)) for KNO3 production can be obtained by the following eq:24,25

P(kWhkg −1) =

1 m

∫0

number of the counterions, nc is the number of the cell pair, U is the applied potential (V), and I is current (A).



RESULTS AND DISCUSSION Chemical and Structural Characterization of the IonExchange Membrane (IEM). Styrene and divinylbenzene base interpolymer ion exchange membranes are synthesized for MED. These membranes are very inert (from pH 2−13) in nature due to polyethylene as a base matrix. Figure S-1 shows the FTIR spectra of IEMs. Peaks at 1644 and 1468 cm−1 are CC and −C−H vibrations of alkene and alkane, respectively. The 1116 cm−1 frequency is due to C−N stretching. The vibrational frequency at 1806 cm−1 is due to the CO band of the amide group. A strong peak at 1036 cm−1 shows the C−O stretching. Frequency at 1066 cm−1 shows the C−O stretching. Both the CEM and AEM display almost similar spectra due to the presence of polyethylene, styrene, and divinylbenzene. The peak at 2925 cm−1 corresponds to the C−H stretching of alkane. 2355 cm−1 is due to the presence of the CN group. The broad peak near 3445 cm−1 shows N−H stretching. The peak at 3733 cm−1 corresponds to the O−H vibration of the alcohol group. The surface morphology of AEM and CEM were investigated by SEM analysis. The surface of the membranes was found to be smooth as shown in Figure S-1. Physicochemical and Electrochemical Properties of the IEM. Table 1 shows the physicochemical and electrochemical properties of IEMs used for MED. The thickness of these membranes measured by screw gauge is found to be 150 μm for AEM and 180 μm for CEM, which is sufficiently enough for the process. Water content and ion-exchange capacity (IEC) for IEMs are estimated as reported earlier.26,27 CEM exhibited about 22% water content, while AEM showed about 16%. IEC values show the number of fixed charge group present in the membranes.27,28 An increase in hydrophilic species with the IEC in the membrane matrix is also responsible for ionic conduction in membranes. The IEC values for the both IEMs were reasonably good and are presented in Table 1.

t

UIdt

(2)

The CE, defined as the fraction of Coulombs utilized for the salt removal, may be obtained by

η=

FnV (C0 − Ct ) t

nc ∫ Idt 0

× 100 (3)

where η is the CE (%), F is the Faraday constant (A·h/mol), V is the volume of the dilution (dm−3), Co and Ct (mol) are the concentration of the dilute compartment at zero time and time t, n is the charge 3222

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mechanical properties of the IEMs are evaluated by DTMA analysis and shown in Figure 3. The elastic modulus of AEM

Table 1. Membrane Thickness (L), Ion-Exchange Capacity (IEC) (Dry Membrane), Membrane Conductivity (ϕM), Counterion Transport Number (tM),a and Water Uptake (UW) Values for IEMs IEM

L (μm)

IEC(meq g−1)

ϕM (mS cm−1)

AEM CEM IONSEP-A IONSEP-C nafion

150 180 420 420 180

1.41 1.32 2.00 2.2 0.9

8.12 9.56 10.5 9.98 12.21

t

M

0.92 0.91 0.92 0.91 0.95

UW(%) 22 16 40 37 22

ref

22 22

a

Activity coefficient values of 0.798 and 0.922 are used for 0.1 and 0.01 M NaCl solutions. Figure 3. Thermo-mechanical analysis for ion exchange membranes.

The ionic conductivity of the membranes is calculated by the membrane resistance in equilibration with 0.1 M NaCl solutions and presented in Table 1. Ionic conductivity of CEM is calculated to be 9.56 mS·cm−1 and 8.12 mS·cm−1 for AEM, which matched with the earlier reported values.23 A potential difference is generated across the membrane when different concentrations of electrolyte solutions passed from both the surfaces. The magnitude of the membrane potential depends on ionic conductivity and IEC of the membrane as well as the concentration of the electrolyte solutions.26 The membrane’s selectivity is also an important parameter which influences the transport of counterions through the membranes. Counterion transport number values are calculated from membrane potential measurements and found to be 0.92 for AEM and 0.91 for CEM.27 The physico and electrochemical properties of prepared membranes are compared with commercially available IONSEP anion and cation exchange membranes supplied by Hangzhou Iontech Environmental Technology Co., Ltd., Zhejiang, China and shown in Table 1. Thermal and Mechanical Properties of IEM. Thermal and Mechanical properties of IEMs are measured using TGA, DMA, and UTM analysis. For all thermal and mechanical analysis, dry membranes are used except for UTM analysis where wet membranes are also used. Figure 2 shows the weight

and CEM is calculated to be 920 and 650 MPa, respectively, and the temperature of tan δ for AEM and CEM is calculated to be 109.2 and 100.15 °C, respectively. The strain−stress curve for AEM and CEM in dry and wet states are presented in Figure 4, and the corresponding values of elastic modulus,

Figure 4. Stress versus strain spectra for ion exchange membranes.

maximum stress, and elongation at break are presented in Figure 5. The elastic modulus for AEM is calculated to 9.06

Figure 5. Mechanical parameters for ion exchange membranes at wet and dry conditions. Figure 2. TGA thermograph for ion exchange membranes.

MPa and 4.91 for CEM, while 4.05% elongation was shown in AEM and 14.24% for CEM. The elongation for both membranes is increased by 113% and 158% for AEM and CEM in their wet states. The mechanical and thermomechanical properties of prepares IEMs are found to be better than commercially available IEMs and are flexible in nature.26−29 Current−Voltage (i−v) Characteristics of MED. Characteristic regions viz. Ohmic, non-Ohmic, and plateau length are shown in Figure 6 during i−v measurements before the

loss spectra for both AEM and CEM. Three step weight losses are observed for both membranes. The first weight loss between 100 and 110 °C is due to the free water present in the membranes; the second weight loss between 250 and 300 °C is due to the degradation of functional groups presents in the AEM. The final weight loss at about 470 °C is due to the degradation of polymers. Membranes show the good thermal properties and stability at higher temperature. Thermo3223

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increases and that after particular time it decreases. The decrement in current density is due to the initial concentration difference between consecutive compartments. This is due to the fact that potassium and nitrate ions are transported by diffusion and migration (the amount of ions transferred by diffusion is much lower than that transferred by migration) into the compartment initially filled with water. After a certain time, the decrease in the current density is caused by the depletion of the electrolyte. During the MED experiments, four different feed concentrations (0.1, 0.2, 0.5, and 1.0 M) of KCl and NaNO3 are applied, and the product of compartments 2 and 4 are maintained with time. ICP and IC analysis is used for the concentration of ions in the product. The effect of applied potential for the conversion of KCl to KNO3 during the MED process is studied. Four potentials (1.5, 2.0, 2.5, and 3 V/cell pair) are applied in different sets of experiments during MED. It is clear from Table 2 that the 2 V/cell pair is found to be the

Figure 6. Current against applied potential for the MED process.

actual experiments with 0.1 M KCl and NaNO3 solution. The potential is varied from 0.5−5 V/cell pair in the step of 0.5 V. It is clear from the graph that current density increases linearly with the applied potential from 0.5 to 1.5 V/cell pair and thus shows the ohmic behavior. From the 1.5 to 2.5 V/cell pair, the graph shows comparatively low change in current, and above the 2.5 V/cell pair, the current density again changes rapidly. So the region where changes in current are minimum is of interest.24 The limiting current density calculated from Figure 6 is 1.58 mA/cm2. Conversion of KCl into KNO3 during the MED Process. Modified ED is used for the conversion of KCl into KNO3 (Figure 1). The feed solution for compartments 1 and 3 are KCl and NaNO3, respectively, and deionized water is fed in compartments 2 and 4. One liter of water is circulated in each of the compartments. Na2SO4 solution is used as the electrode wash solution during the experiment. Feed solutions are separated by cation and anion-exchange membranes, arranged alternately. All of the experiments are performed in an external electric field of 2 V/cell pair. Corresponding ions are migrated through the IEMs to the adjacent compartment with applied potential. K+ ions moved from compartment 1 to 2 and NO3− ions migrated from compartment 3 to 2. Similarly, the Cl− ion migrated from compartment 5 to 4, while the Na+ ion migrated from compartments 3 to 4. As a result, compartments 1 and 3 were diluted, while compartments 2 and 4 became to concentrated. The overall result of the MED process is similar to that of the ED process. Figure 7 shows the current density against time during the production of KNO3 by the MED process. It is clear from the figure that initially current density

Table 2. Energy Consumption (P) and Current Efficiency (CE %) for the Production of KNO3 with Different Applied Potentials applied potential (per cell pair) 1.5 2.0 2.5 3.0

V V V V

P (kwh·kg−1)

CE %

0.74 0.82 1.04 1.31

72 83 83.9 83.7

more economic and efficient process for MED during KNO3 production. Figure 8a−d shows the dependence of KCl and KNO3 concentrations upon time during the MED process with different concentrations of KCl and NaNO3 in feed solutions. At 2 V/cell pair applied potential, the concentration of KCl decreases from its initial value of 0.124 to 0.025 M, while 0.117 M KNO3 concentration is built up in the second compartment within the 120 min (Figure 8a). However, the change in the fourth compartment is also recorded and found to be 0.076 M NaCl at the end of the experiment as shown in Figure 9. In the same experiment on changing the feed concentration from 0.1 to 0.2 M KCl, the production of KNO3 is about 0.18 M in 210 min, and the change in the fourth compartment from 0 to 0.2 M of NaCl. Figure 8c,d shows the change in concentration of KNO3 with a feed of 0.5 and 1.0 M KCl solution, and it can be seen that all of the KCl is converted to KNO3 in the second compartment and NaCl in the fourth compartment. The conversion rate is found to be about 90−97% in all of the MED experiments in the case of KNO3, as shown in Figure 10. The 1.0 M KCl conversion takes more time than the 0.1 M conversion due to the presence of more co-ions present in solution. Co-ion transport across the membrane regulates the obtained product purity.30−32 During the course of MED experiments, co-ion transport from one compartment to another was also observed to ensure the product purity during KNO 3 production, and similarly, no contamination of K+ is found in the NaCl compartment. In the whole experiment, the amount of Na+ in the KNO3 compartment and K+ in the NaCl compartment is almost constant with time, and the product solution is found to be free from impurities. This is due to the low free volume inside the interpolymer based membranes. Because of the electro-osmosis drag, the volume of product compartments increased as water molecules passed the

Figure 7. Current density against time during the production of KNO3 by the MED process. 3224

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Figure 8. (a) Dependence of KCl and KNO3 concentrations upon time during the production of KNO3 by the MED process with 0.1 M KCl and 0.1 M NaNO3. (b) Dependence of KCl and KNO3 concentrations upon time during the production of KNO3 by the MED process with 0.2 M KCl and 0.2 M NaNO3. (c) Dependence of KCl and KNO3 concentrations upon time during the production of KNO3 by the MED process with 0.5 M KCl and 0.5 M NaNO3. (d) Dependence of KCl and KNO3 concentrations upon time during the production of KNO3 by the MED process with 1 M KCl and 1 M NaNO3.

membrane along with hydrated ions.33,34,35 During electroconversion experiments, the volume of all compartments were found to be constant up to 0.5 M KCl feed solution, but at higher feed solution (1.0 M) 2−3% water was dragged into the product compartment and reduced the KNO3 concentration. The mass balance before and after the experiments are calculated and found with initial 0.1 M KCl and 0.1 M NaNO3; the final product was 0.096 M KNO3 A M NaCl (A = 0.1, 0.2, 0.5, and 1 M). This shows the complete mass balance during the conversion of KCl. Energy Consumption and Current Efficiency during the MED Process. Energy consumption and current efficiency data to evaluate the performance of MED during the conversion of KNO3 with different applied potential are shown in Table 2. It is observed that P increased as well as CE with the increase in applied potential from 1.5 V/cell pair to 3 V/cell pair. The CE and P at 1.5 V potential are found to be 72% and 0.74 kWh kg−1 respectively, while they were 83.0% and 0.82 kWh kg−1 at 2 V/cell pair applied potential. The CE at 2.5 and 3.0 V/cell pair potential are calculated to be similar to the 2 V/cell pair with higher energy consumption. Energy consumption for 2.5 and 3 V/cell pair is higher than that of the 2 V/cell pair of a magnitude of 27% and 59% respectively. The 2 V/cell pair applied potential was found to be most suitable for KNO3 production by MED.

Figure 9. Dependence of NaCl concentrations upon time during the MED process with different feeds of KCl and NaNO3.



CONCLUSIONS MED experiments are performed to confirm its potential for the conversion of potassium nitrate. From current voltage characteristics, it is observed that the MED system gives its best performance when operated between 1.5 and 2.5 V/cell pair, out of which the 2.0 V/cell pair is found to be the most suitable

Figure 10. Conversion of KNO3 from KCl by the MED process with different feeds of KCl.

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(11) Bell, D. A.; Sardisco, J. B.; Anderson, N. E.; Caldwell, J. S. Potassium sulfate and potassium sulfate fertilizers manufactured from potassium chloride. Potash Technol. 1983, 583. (12) Pfeiffer, R. W.; DiFranco, V. J.; Albright, L. F. Albright, Potassium nitrate production using a molten salt technique. J. Agric. Food Chem. 1967, 15 (6), 949−953. (13) Marcus, V.; Per, E. Process for Producing High-Purity Potassium Salts. U.S. Patent 6274105, 2001. (14) Michael, B.; Eyal, G.; Akiva, M.; Eyal, B.; Hugo, K.; Gideon, F.; Ron, F.; Cornelis, P. L. Process for Production of Commercial Quality Potassium Nitrate from Polyhalite. U.S. Patent, 8388916, 2013. (15) Abidaud, A. Continuous Production of Potassium Nitrate via Ion Exchange. U.S. Patent, 5110578, 1992. (16) Ion Exchange Process for Producing Potassium Nitrate. China Patent CN 1056819, 2000. (17) Dotson, R. L.; Miles, R. C.; Carpenter, L. D. Electrochemical Production of KNO3 /NaNO3 Salt Mixture. U.S. Patent 4465568, 1984. (18) O’Leary, K. J.; Hora, C. J.; DeRespiris, D. L. Production of Alkali Metal Carbonates in a Cell Having a Carboxyl Membrane. U.S. Patent US4147599, 1979. (19) Jaroszek, H.; Lis, A.; Dydo, P. Synthesis of Potassium Nitrate by Metathesis-Electrodialysis. Membranes and Membrane Processes in Environmental Protection, Monographs of the Environmental Engineering Committee, Polish Academy of Sciences; Polish Academy of Science: Warsaw, Poland, 2014; Vol. 119, pp 351−361. (20) Thampy, S. K.; Joshi, B. S.; Govindan, K. P. Preparation of potassium carbonate by electrodialysis technique. Indian J. Technol. 1985, 23, 454−457. (21) Dinda, M.; Chatterjee, U.; Kulshrestha, V.; Sharma, S.; Ghosh, S.; Desale, G. R.; Shahi, V. K.; Makwana, B. S.; Maru, P. D.; Bhadja, V.; Maiti, S.; Ghosh, P. K. Sustainable synthesis of a high performance inter-polymer anion exchange membrane employing concentrated solar radiation in a crucial functionalization step. J. Membr. Sci. 2015, 493, 373−381. (22) Kulshrestha, V.; Chatterjee, U.; Sharma, S.; Makwana, B. S.; Maru, P. D. Large scale preparation of polyethylene based Ion exchange membranes and their application for Water desalination. Macromol. Symp. 2015, 357 (1), 194−199. (23) Gahlot, S.; Sharma, S.; Kulshrestha, V. Electrodeionization: An Efficient way for removal of fluoride from tap water using an aluminum form of phosphomethylated resin. Ind. Eng. Chem. Res. 2015, 54, 4664−4671. (24) Gahlot, S.; Sharma, P. P.; Gupta, H.; Kulshrestha, V.; Jha, P. K. Preparation of Graphene Oxide composite Ion exchange membranes for Desalination Application. RSC Adv. 2014, 4, 24662−24670. (25) Gahlot, S.; Sharma, P. P.; Kulshrestha, V. Dramatic Improvement in Ionic Conductivity and Water Desalination Efficiency of SGO composite Membranes. Sep. Sci. Technol. 2015, 50, 446−453. (26) Sharma, P. P.; Gahlot, S.; Bhil, B. M.; Gupta, H.; Kulshrestha, V. An environmentally friendly process for the synthesis of an fGO modified anion exchange membrane for electro-membrane applications. RSC Adv. 2015, 5, 38712−38721. (27) Sharma, P. P.; Kulshrestha, V. Synthesis of highly stable and high water retentive functionalized biopolymer-graphene oxide modified cation exchange membranes. RSC Adv. 2015, 5, 56498− 56506. (28) Gahlot, S.; Kulshrestha, V. Dramatic Improvement in Water Retention and Proton Conductivity in Electrically Aligned Functionalized CNT/SPEEK Nanohybrid PEM. ACS Appl. Mater. Interfaces 2015, 7, 264−272. (29) Gahlot, S.; Sharma, P. P.; Kulshrestha, V.; Jha, P. K. SGO/SPES based Highly Conducting Polymer Electrolyte Membranes for Fuel Cell application. ACS Appl. Mater. Interfaces 2014, 6, 5595−5601. (30) Gahlot, S.; Sharma, P. P.; Gupta, H.; Jha, P. K.; Kulshrestha, V. Synthesis of SPEEK/TiO2 Nano-Composites and Their Characterization. Adv. Electrochemistry 2014, 2 (1), 90−95.

for our experiments. The product potassium nitrate is obtained with high purity at low energy consumption and adequate current efficiency. The prepared interpolymer based membranes show excellent electrochemical and physicochemical properties with good thermal and mechanical stabilities. Membranes are also very suitable due to their very low electro-osmotic drag during MED experiments. The results show that MED is found to be an alternative route for the production of high quality potassium nitrate at an industrial scale.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b00248. Details of the chemical, structural, and physiochemical characterization and membrane stability and FTIR spectra SEM images of for ion exchange membranes (PDF)



AUTHOR INFORMATION

Corresponding Author

*Tel: +91-278-2567039. Fax: +91-278-2567562. E-mail: [email protected]; [email protected] Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS We are thankful to CSIR Network project CSC 0105 for providing financial support to perform this work. We are also thankful to Analytical Discipline and Centralized Instrument facility, CSMCRI, Bhavnagar for instrumental support.



REFERENCES

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DOI: 10.1021/acssuschemeng.6b00248 ACS Sustainable Chem. Eng. 2016, 4, 3220−3227

Research Article

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DOI: 10.1021/acssuschemeng.6b00248 ACS Sustainable Chem. Eng. 2016, 4, 3220−3227

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