Article pubs.acs.org/IECR
Chlorohydrination of Allyl Chloride to Dichloropropanol in a Microchemical System Jisong Zhang, Jing Tan, Kai Wang, Yangcheng Lu,* and Guangsheng Luo* The State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China ABSTRACT: A microchemical system, including two micromixers and a delay loop, is specially designed to carry out the chlorohydrination of allyl chloride with chlorine in water. Chlorine is dissolved in water in the first micromixer and then reacts with allyl chloride to produce dichloropropanol in the second micromixer. The reaction can be accomplished in the delay loop with a residence time less than 10 s and the selectivity higher than 98%. A multistage strategy which connects several microchemical units in series has been developed and demonstrated. The dichloropropanol concentration higher than 6 wt % with the selectivity higher than 96% can be successfully reached using this strategy. The results show that low temperature and high pressure could greatly improve the microreaction performance. In contrast to the conventional reaction process, the microreaction process has the advantages for higher yield, higher dichloropropanol concentration, less water waste, and lower energy consumption. Moreover, the new process could make the reaction process employing chlorine more controllable and safe.
1. INTRODUCTION The classical chlorohydrination of allyl chloride is an important step in the production of epichlorohydrin (ECH), an important raw material for producing epoxy resins and elastomers.1,2 The process is performed by reacting allyl chloride, water, and chlorine in a dilute aqueous phase. In this case, dichlorohydrin (DCP) is formed as the product while hydrogen chloride and 1,2,3-trichloropropane are primarily byproducts.3 Dichlorohydrin is a term employed to designate the isomers 1,3-dichloro-2-hydroxypropane (1,3-DCP) and 2,3-dichloro-1-hydroxypropane (2,3-DCP). The saponification or dehydrochlorination is then accomplished by treatment of the dichlorohydrin solution with
caustic soda or slurry of lime. Epichlorohydrin and other organics are steam-stripped from the resulting sodium chloride or calcium chloride brine.4 A disadvantage of the known chlorohydrination processes is that various chlorinated organic compounds can be formed as well as the desired dichlorohydrin which reduces the yield. Furthermore, the process is generally difficult to perform, because of the hazardous and highly reactive nature of the chlorine gas. Also, substantial amounts of water are used to reduce formation of undesired byproducts, producing large effluent streams. The chlorohydrination of allyl chloride with chlorine in water is shown as follows:
The process is poorly understood; the available information devoted to the chlorohydrination of other alkenes5,6 leads to the conclusion that the mechanism for the formation of dichloropropanol is through the chloronium ion intermediate. In strongly solvating media such as water, the chloronium ion intermediate is formed on the electrophilic addition of chlorine to allyl chloride. Since the solubility of allyl chloride in water is low, the oil phase is easily formed when the concentration of allyl chloride is increased. In that case, chlorine is dissolved in the oil phase The chloronium ion intermediate can react with water to produce the desired dichloropropanol, with chloride ion to produce 1,2,3-trichloropropane, or with dichloropropanol to produce tetrachloropropyl. © 2012 American Chemical Society
Received: Revised: Accepted: Published: 14685
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Figure 1. Schematic overview of the experimental setup.
and the addition reaction of chlorine to allyl chloride (eq 4) proceeds in the preference of the desired reaction. As a result, the byproduct of trichloropropane is increased. Furthermore, the side reaction of chloride ion with chloronium ion intermediate dramatically restricts the possibility of obtaining highly concentrated solutions of dichlorohydrins. That is the reason why the reaction has to proceed in a very dilute solution to suppress the side reaction. As a result, a recirculation system which has a large recycle loop (about 5)3 compared to the product of DCP solution has to be used to maintain the yield. This results in high energy consumption and a large reactor volume.
In our previous study, a microchemical system has been successfully used in the fast exothermic reaction of the Beckmann rearrangement of cyclohexanone oxime18 and the reaction between cyclohexanecarboxylic acid and oleum, a critical step in the SNIA (the name of an Italian company as inventor) toluene route for the preparation of caprolactam.19,20 In this work, a new microchemical system, including two micromixers and a delay loop, was specially designed to carry out the chlorohydrination of allyl chloride with chlorine in water. To the best of our knowledge, it is the first time this reaction was realized in a microsystem. The objective of this microsystem is to enhance the mixing of reactants, accomplish the reaction in a short residence time, and then reduce the byproducts. It can continuously realize the two-step reaction and improve the efficiency. Chlorine was dissolved in water in the first micromixer and then reacted with allyl chloride in the second micromixer. The chlorohydrination reaction proceeded in the delay loop connected directly to the second micromixer. The influences of reaction temperature, reactant flow rate, and Cl− concentration on selectivity were studied. To increase the DCP concentration, a multistage strategy which connects several microchemical units in series has been developed and demonstrated. Low temperature and high system pressure were applied to improve the reaction performance.
Continuous flow microreactors have made rapid progress over the past decade with extensive applications in chemical synthesis.7−9 Enhancement of heat and mass transfer characteristics,10 improvement of selectivity and yield,11,12 and controllable synthesis of dangerous compounds13,14 are well realized using microreactors. Besides, microreactors can conduct multiple reaction steps at various conditions and improve efficiency.15−18 In the chlorohydrination process, the designed microreactors allow for the careful control of the hazardous and highly reactive chlorine gas and can regulate the contact between chlorine and water. The microsystem can continuously realize the two-step reaction including chlorine dissolution in water at the first micromixer and the chlorohydrination process in the delay loop after the second micromixer. The enhanced mixing performance and mass transfer characteristics between allyl chloride and chlorine water (water containing dissolved chlorine) can reduce the oil phase and enhance the main reaction rate which increases the yield and selectivity and even gain a more concentrated solution of DCP, reducing the large effluent streams. Furthermore, the continuous-flow synthesis instead of recycle process in the conventional process can also reduce reactor volume and the energy consumption.
2. EXPERIMENTAL SECTION 2.1. Reagents. Epichlorohydrin (ECH) (C3H5ClO, analytical grade) and allyl chloride (C3H5Cl, 98%) were purchased from J&K Scientific Ltd. (Beijing); chlorine (Cl2, 99.5%) was from Jiangsu Anpon Electrochemical Co., Ltd. 2.2. Equipment. A schematic of the microsystem setup is shown in Figure 1. In this work, Cl2 gas from the cylinder was provided via a mass flow controller (Beijing Metron Instruments Co. Ltd.) at a flow rate of 3−30 SCCM, where SCCM denotes mL min−1 at the standard condition of 20 °C and 1 bar. Water was delivered by metering pumps (Beijing Satellite Co. Ltd.) at a flow rate of 2−9 mL min−1. Allyl chloride was pumped into the second microreactor with a syringe pump 14686
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Figure 2. Chlorohydrination of allyl chloride in the microsystem.
(Baoding Longer Precision Pump Co. Ltd.) at a flow rate of 0.012−0.12 mL min−1. The mixing was performed in a microvolume Y-shaped mixer (Beijing Mingnike Analytical Instrument Center). The micromixer is made of PEEK (polyether ether ketone) material with an inner diameter of 0.25 mm. The Y-shaped micromixer has been applied for the gas/liquid and liquid/liquid dispersion in previous literature.21−23 Water and Cl2 gas flowed through the pipes immersed in Water Bath 1 to control the feeding temperature. A delay loop (polytetrafluoroethylene, PTFE) immersed in Water Bath 2 with an inner diameter of 1 mm and an external diameter of 1.6 mm was connected directly downstream to the second micromixer to control the reaction time. The tube between the two micromixers was the same with the delay loop except for a length of 0.4 m. The PEEK and PTFE materials were all compatible with the corrosive gas Cl2 and the chlorine water. The pressure was controlled by a metering valve (Beijing Xiongchuan technology Ltd.), and check valves (Beijing Xiongchuan technology Ltd.) were used to avoid the reverse flow. 2.3. Analysis. During the experiment, water and chlorine gas contacted in the first Y-shaped mixer and then mixed with allyl chloride in the second micromixer. The reaction was completed in the following delay loop. After about 3 min, the system is stable (estimated from the pH of the product), and then, the samples were collected directly at the outlet of the microsystem and weighed by an electronic analytical balance (Mettler Toledo AL204). The sample was diluted by phosphate buffer solution and measured by gas chromatography (Shimadzu GC-2014) with a flame ionization detector under the following conditions: the injection temperature, 220 °C; the column temperature, 70−220 °C, 30 °C min−1; the detector temperature, 280 °C. The sample volume for all analyses was 2 μL. The dichloropropanol selectivity S was calculated by the following equation. S=
velocity is low. As chlorine can be dissolved in water, the chlorine bubbles in water get smaller and even disappear before the addition of allyl chloride if the flow rate of chlorine gas is less than its solubility in water. Chlorine is hydrolyzed in water to hypochlorous acid and hydrochloric acid as follows:25 Cl 2 + H 2O ⇌ H+ + Cl− + HClO
(6)
In the second mixer, allyl chloride is dispersed into the chlorine water as liquid droplets because of the low solubility of allyl chloride in water. Allyl chloride transfers to the aqueous phase from the liquid droplets and the chlorohydrination is carried on according to the equations of 2 and 3. As the reaction goes on, the undissolved chlorine and the liquid droplets of allyl chloride are both consumed forming the DCP solution. If the gas bubbles come in contact with the liquid droplets directly, the side reaction of the addition reaction of chlorine to allyl chloride (eq 4) increases greatly. This means that, if the addition of chlorine gas exceeds its solubility in water, the undissolved chlorine would increase the side reaction and reduce the selectivity. To understand the dispersion scale of allyl chloride in the second mixer, water is used as the continuous phase and allyl chloride as the dispersed phase. The formed allyl chloride droplets are observed at an enlargement area. A microscope with a CCD video camera (PL-A742, PixeLINK, Canada) is used to record the formed droplets. The droplet diameters and their pictures are shown in Figure 3. In previous reports,26,27 the
W1,3‐DCP + W2,3‐DCP W1,3‐DCP + W2,3‐DCP + Wby‐pro
(5)
where W1,3‑DCP (%) is the mass fraction of 1,3-DCP in the sample, W2,3‑DCP (%) is the mass fraction of 2,3-DCP in the sample, and Wby‑pro (%) is the mass fraction of byproducts (1,2,3-trichloropropane and tetrachloropropyl) in the sample. By this method, the selectivity (measured in percentage) is determined within a measurement error of 0.5%.
3. RESULTS AND DISCUSSION 3.1. Chlorohydrination Process in the Microsystem. In the microsystem, water and Cl2 gas mix in the first mixer and then react with allyl chloride in the second micromixer. The reaction process is sketched in Figure 2. A bubbly flow24 usually occurs in the channel after the first mixer when the chlorine gas
Figure 3. Diameters and microphotographs of allyl chloride droplets at different operating conditions. (a) The droplet diameters at different flow rates of water; (b) water flow rate: 5 mL min−1; allyl chloride flow rate: 40 μL min−1; (c) water flow rate: 7.5 mL min−1; allyl chloride flow rate: 60 μL min−1; (d) water flow rate: 10 mL min−1; allyl chloride flow rate: 80 μL min−1. 14687
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range of 20−60 °C unless it is above 60 °C. In order to ensure both conversion and selectivity, the volumetric ratio of Cl2 to H2O ranges from 1 to 1.53 in industrial production. In our experiments, the selectivity higher than 98% can be reached when the volumetric ratio of Cl2 to H2O is 1.5 or 2. This is due to the enhanced mixing performance and mass transfer characteristics between allyl chloride and water in the microsystem which can reduce the side reaction and increases the selectivity to DCP. The vaporization of allyl chloride (boiling point at normal temperature and atmospheric pressure: 45 °C) has been observed in the experiments at the temperature above 60 °C. The allyl chloride gas results in an increased contact with chlorine which could enhance the side reaction. As shown in Figure 4, the selectivity decreases obviously when the volumetric flow ratio of Cl2 to H2O is raised to 3. This is because chlorine gas flow exceeds its solubility in water (one volume of water can dissolve about two volumes of chlorine at 30 °C).29 The undissolved chlorine can easily react with allyl chloride and form byproducts. When the volumetric flow ratio of Cl2 to H2O is 1, the concentration of DCP solution gained is about 0.58 wt %. That means at present conditions it can just gain the DCP solution concentration of 1.16 wt % without decreasing the selectivity. 3.3.2. Effect of Flow Rate of Reactants. Figure 5 shows the effect of water flow rate and volumetric flow ratio of Cl2 to H2O
droplet diameter is predicted by the capillary number (Ca): d∝1/Ca, Ca = μcuc/γ, where μc is the viscosity of continuous phase (here, the water), γ is the allyl chloride/water interfacial tension, and uc is the velocity of continuous water. As expected, the droplet size reduces with the increase of the flow rate. The droplet diameter in the microsystem ranges from about 40 to 160 μm, which is good and sufficient to realize the reaction, and larger interfacial area for the mass transport process can be obtained in this microsystem. Because of the small dispersion scale and large interfacial area in the microsystem, allyl chloride can be transferred quickly to aqueous phase and reduce the contact with chlorine and then improve the selectivity. It is sure that much smaller droplet can be obtained with other fluids and micromixers,28 but cost and clogging risk will sharply increase as well. 3.2. Conversion. The flow rates of water, chlorine gas, and allyl chloride are 5 mL min−1, 7.5 mL min−1, and 30 μL min−1, respectively, which means that the molar ratio of allyl chloride/ Cl2 is kept at 1.1. The temperature of Water Bath 1 is 30 °C while Water Bath 2 has a range of 20−80 °C. The system pressure is at atmospheric pressure. The delay loop after the second mixer is 1 m long which means that the residence time of the reactants in the channel is 9.4 s. During the reaction, even at 20 °C, chlorine is almost expended and the conversion of Cl2 is approximately 100% from the fact that the collected samples are acidic and the pH of the solution does not change anymore. Compared with more than 10 min of residence time in the conventional process,3 the results indicate that the microsystem enhances the chlorohydrination reaction and can accomplish the process within 10 s. It is mainly because of the decrease in dispersion scale of allyl chloride and the following strongly enhanced mass transfer rate between allyl chloride and water. To draw any further conclusion, more work has to be done to investigate the kinetics of the chlorohydrination and the mass transfer characteristic in the microsystem. 3.3. Selectivity. 3.3.1. Effect of Reaction Temperature. Figure 4 shows the effect of reaction temperature and volumetric
Figure 5. Effect of water flow rate and volumetric flow ratio of Cl2 to H2O on the selectivity of DCP. The experimental conditions: water, 2−9 mL min−1; chlorine gas, 3−27 mL min−1; allyl chloride, 12−108 μL min−1. The molar ratio of allyl chloride/Cl2 is kept at 1.1. The temperature of Water Bath 1 is 20 °C while Water Bath 2 is at 30 °C. The system pressure is at atmospheric pressure.
on the selectivity. The high selectivity can reach to about 99% as volumetric flow ratio of Cl2/H2O is 1.5 or 2. The temperature of Water Bath 1 is decreased to 20 °C for chlorine dissolution. We can find a slight increase in the selectivity (from 98% to 99%) when the other conditions are the same. The possible reason is that lower temperature can increase the solubility of chlorine in water which can reduce the undissolved chlorine and then reduce the side reaction. The decrease in selectivity is also found when the volumetric flow ratio of Cl2 to H2O is raised to 3. However, the selectivity increases when the volumetric flow ratio of Cl2 to H2O is raised from 1.5 to 2 with the flow rate below 4 mL min−1. The reason may be the bad mixing performance because of the extremely low flow rate with Cl2/H2O of 1.5. Of course, the selectivity improves with the increase of water flow rate especially when the flow rate is below 5 mL min−1, indicating that the flow rate has a large effect on the selectivity. As shown in Figure 3, the flow rate of water has a large influence on the diameters of allyl chloride droplets. When the flow rate is increased from 5 to 10 mL min−1,
Figure 4. Effect of reaction temperature and volumetric flow ratio of Cl2 to H2O on the selectivity of DCP. The experimental conditions are as follows: water, 5 mL min−1; chlorine gas, 7.5, 10, and 15 mL min−1; allyl chloride, 30, 40, and 60 μL min−1. The molar ratio of allyl chloride/Cl2 (based on the overall feed ratio) is 1.1. The temperature of Water Bath 1 is 30 °C while Water Bath 2 had a range of 20−80 °C. The system pressure is at atmospheric pressure. The delay loop after the second mixer is 2 m.
flow ratio of Cl2 to H2O (based on the overall feed ratio) on the selectivity of DCP. In order to ensure the conversion, the length of delay loop is 2 m in the following experiments. As the reaction is proceeding in a very dilute solution, the temperature rise of reactants in the experiments can be ignored. The reaction temperature shows little effect on selectivity in the 14688
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the droplets diameters decrease from about 160 to 40 μm. With smaller dispersion scale and larger interfacial area in the microsystem, allyl chloride can be transferred quickly to aqueous phase and reduce the contact with chlorine and then improve the selectivity. The results indicate that the mixing performance between allyl chloride and chlorine water plays a crucial role in improving the selectivity. Figure 6 shows the effect of molar ratio of allyl chloride to chlorine (based on the overall feed ratio) and volumetric flow Figure 7. Schematic overview of the multistage strategy. Each stage includes two micromixers and a delay loop.
2,3-DCP 70%) mass fraction of 1, 2, 3, 4, and 5 wt % and equal molar chloride ions provided by NaCl (mass fraction: 0.45, 0.90, 1.36, 1.80, and 2.27 wt %). Figure 8 shows that the simultaneous increase of DCP and NaCl concentration has a negative effect on the selectivity.
Figure 6. Effect of molar ratio of allyl chloride to chlorine and volumetric flow ratio of Cl2 to H2O on the selectivity of DCP. The experimental conditions: water, 5 mL min−1; chlorine gas, 7.5, 10, and 15 mL min−1; allyl chloride, 16−109 μL min−1. The molar ratio of allyl chloride/Cl2 ranges from 0.6 to 2.0. The temperature of Water Bath 1 is 30 °C while Water Bath 2 is 30 °C. The system pressure is at atmospheric pressure.
ratio of Cl2 to H2O on the selectivity. It can be concluded that the molar ratio of allyl chloride to chlorine has a large influence on the selectivity. When the molar ratio is below 1, the selectivity is low. The excess chlorine increases the risk of side reaction. When the molar ratio is above 1, the selectivity can reach a high value and improve slightly with the increase of the molar ratio. The effect is especially obvious when the volumetric flow ratio of Cl2 to H2O is 3. This is why the molar ratio of allyl chloride/Cl2 is kept from 1 to 1.02 in industrial production.3 It can ensure the high selectivity to DCP and also reduce the use of expensive allyl chloride. In other experiments, the molar ratio is usually kept at 1.1 which is a little larger than the reference value in industrial production. This is due to the extremely small flow rate of allyl chloride (μL min−1), and it is difficult to control its flow rate as accurately as industry does. Such a choice can ensure the complete conversion of chlorine and safe operations. 3.4. Multistage Strategy to Produce Highly Concentrated DCP Solution. The selectivity decreases when the volumetric flow ratio of Cl2 to H2O is increased as shown in Figures 4, 5, and 6. That means it can just gain the DCP solution concentration of 1.16 wt % (4−6 wt % in the industrial process3) in the single-stage microsystem without decreasing the selectivity. In order to increase the DCP concentration, a multistage strategy may be applied; i.e., the DCP solution gained in the anterior microreactor is pumped into the posterior mixers for dissolving chlorine and allyl chloride in sequence to carry out the continued reaction (Figure 7). In the chlorohydrination reaction, a molar hydrogen chloride per molar DCP is produced. That means that the produced DCP solution is strongly acidic which cannot be pumped by the metering pump. In order to investigate the negative effect of chloride ions on the reaction, we designed a set of experiments to simulate the process. The solution is prepared with a DCP (1,3-DCP 30%,
Figure 8. Effect of DCP and corresponding NaCl concentration on the selectivity. The experimental conditions: water, 5 mL min−1; chlorine gas, 4−15 mL min−1; allyl chloride, 16−60 μL min−1. The molar ratio of allyl chloride/Cl2 is at 1.1. The temperature of Water Bath 1 is 20 °C while Water Bath 2 is 30 °C. The concentration of DCP in water ranges from 0 to 5 wt % while Cl− ranges from 0 to 2.27 wt %. The system pressure is at atmospheric pressure.
When the DCP mass fraction is below 3 wt %, the selectivity can reach 97+%. With the increasing DCP concentration, the selectivity decreases to 95+%. The results indicate that it can gain a highly concentrated DCP solution of about 6 wt % with a high selectivity of above 96% by the multistage strategy. The negative effect may come from the increasing Cl− concentration and the decreasing chlorine solubility. The increasing Cl− concentration gives a higher risk of side reaction shown in eq 3. Alkana et al.30 described the solubility of Cl2 in aqueous hydrochloric acid solutions. The results show that the solubility of Cl2 decreases with increasing HCl concentration from 0 to 0.5 mol L−1. The molar concentration of Cl− is 0.39 mol L−1 when the DCP mass fraction is 5 wt %. As a result, the solubility of Cl2 decreases with the increasing DCP mass fraction (0−5 wt %). The increasing undissolved chlorine can react with allyl chloride and decrease selectivity. 3.5. Improvement of Reaction Performance. On the basis of the above results, we find that the solubility of Cl2 in water plays an important role in improving the selectivity. In order to get a higher concentration of DCP solution without decreasing the selectivity at single-stage, some methods have been applied to improve the solubility of Cl2 in water. The usual ways are the lower temperature and high system pressure.31 Figure 9 shows the selectivity at different temperatures of 0, 10, 20, and 30 °C for chlorine dissolution, and Figure 10 shows the effect of system pressure on the selectivity. When the 14689
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fast mass transfer rate (from chlorine and allyl chloride to aqueous phase), the direct contact between chlorine and allyl chloride increases greatly, especially as the flow rates of chlorine and allyl chloride are high in the system. The optimized conditions can reduce the number of stages required to get highly concentrated DCP solution which is very useful for reducing the equipment cost and operation complexity. A performance comparison between the microsystem and conventional process is shown in Figure 11 which indicates that chlorohydrination of allyl chloride in a microchemical system has an advantage over that in the conventional process. It has to employ a recirculation system to ensure the reaction yield in the conventional process, and the residence time is as long as >10 min. The cycle flux is usually much larger than the product flux which requires high energy and large reactor volume. The process in the microsystem, as a continuous flow process, can greatly reduce the energy cost and the reactor volume. Higher than 96% selectivity can be reached in the microsystem compared with 90−93% in the conventional process. In addition, residence time in the microsystem can be reduce to less than 20 s with a more concentrated DCP solution of higher than 6 wt %, reducing the large effluent streams in the following treatment. Finally, the designed microsystem allows for careful control of the hazardous and highly reactive chlorine gas and achieves the process in safety.
Figure 9. Effect of the temperature for chlorine dissolution on the selectivity of DCP. The experimental conditions are as follows: water, 5 mL min−1; chlorine gas, 10−30 mL min−1; allyl chloride, 40−120 μL min−1. The molar ratio of allyl chloride/Cl2 is at 1.1. The temperature of Water Bath 1 ranges from 0 to 30 °C while Water Bath 2 is 30 °C. The system pressure is at atmospheric pressure.
4. CONCLUSIONS In the paper, flow microreactors have been successfully applied to carry out the chlorohydrination of allyl chloride with chlorine in water. The reaction can be safely accomplished in the system with a residence time of less than 10 s and selectivity higher than 98%. The influences of reaction temperature and reactant flow rate on selectivity have been investigated. The results show that a highly concentrated solution of dichloropropanol (6 wt %) can be gained with a high selectivity of above 96% by the multistage technology. Low temperature and high system pressure is beneficial to get higher DCP solution concentration at single-stage without decreasing the selectivity. In contrast to the conventional process, the flow microreaction process has the advantages for higher yield, higher dichloropropanol concentration, less water waste, and lower energy consumption. Moreover, the new process could make the reaction process employing chlorine more controllable and safe.
Figure 10. Effect of system pressure on the selectivity of DCP. The experimental conditions are as follows: water, 5 mL min−1; chlorine gas, 10−30 mL min−1; allyl chloride, 40−120 μL min−1. The molar ratio of allyl chloride/Cl2 is at 1.1. The temperature of Water Bath 1 is 20 °C while Water Bath 2 is 30 °C. The system pressure ranges from 1 to 2.5 atm.
temperature decreases to 10 and 0 °C, the selectivity is obviously improved at the high volumetric ratio of Cl2/H2O. The same improvement is observed in Figure 10 when the system pressure is 2.5 atm. It can get a high selectivity of about 96% at the Cl2/H2O volumetric ratio of 6 (the DCP concentration: 3.34%). With the increase of the solubility of Cl2 in water, the undissolved chlorine is reduced in the system. As a result, the direct reaction between chlorine and allyl chloride decreases and the selectivity is improved. Also, the use of micromixers is very important in the improvement. Without the
Figure 11. Comparison of conventional process and microchemical system. 14690
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palladium catalysts having regular pore systems. Ind. Eng. Chem. Res. 1996, 35, 4412−4416. (17) Wießmeier, G.; Hönicke, D. Microfabricated components for heterogeneously catalysed reactions. J. Micromech. Microeng. 1996, 6, 285−289. (18) Zhang, J. S.; Wang, K.; Lu, Y. C.; Luo, G. S. Beckmann rearrangement in a microstructured chemical system for the preparation of ε-caprolactam. AIChE J. 2011, 58, 925−931. (19) Wang, K.; Lu, Y. C.; Shao, H. W.; Luo, G. S. Improving selectivity of temperature-sensitive exothermal reactions with microreactor. Ind. Eng. Chem. Res. 2008, 47, 4683−4688. (20) Wang, K.; Lu, Y. C.; Xu, J. H.; Gong, X. C.; Luo, G. S. Reducing side product by enhancing mass-transfer rate. AIChE J. 2006, 52, 4207−4213. (21) Kubo, A.; Shinmori, H.; Takeuchi, T. Atrazine-imprinted microspheres prepared using a microfluidic device. Chem. Lett. 2006, 35, 588−589. (22) Steegmans, M. L. J.; Schroën, K. G. P. H.; Boom, R. M. Characterization of emulsification at flat microchannel Y Junctions. Langmuir 2009, 25, 3396−3401. (23) Tan, J.; Du, L.; Xu, J. H.; Wang, K.; Luo., G. S. Surfactant-free microdispersion process of gas in organic solvents in microfluidic devices. AIChE J. 2011, 57, 2647−2656. (24) Abadie, T.; Aubin, J.; Legendre, D.; Xuereb, C. Hydrodynamics of gas−liquid Taylor flow in rectangular microchannels. Microfluid. Nanofluid. 2012, 12, 355−369. (25) Connick, R. E.; Chia, Y. T. The hydrolysis of chlorine and its variation with temperature. J. Am. Chem. Soc. 1959, 81, 1280−1284. (26) Xu, J. H.; Li, S. W.; Tan, J.; Wang, Y. J.; Luo, G. S. Preparation of highly monodisperse droplet in a T-junction microfluidic device. AIChE J. 2006, 52, 3005−3010. (27) Xu, J. H.; Li, S. W.; Tan, J.; Luo, G. S. Correlations of droplet formation in T-junction microfluidic devices: From squeezing to dripping. Microfluid. Nanofluid. 2008, 5, 711−717. (28) Jeong, W. C.; Lim, J. M.; Choi, J. H.; Kim, J. H.; Lee, Y. J.; Kim, S. H.; Lee, G.; Kim, J. D.; Yi, G. R.; Yang, S. M. Controlled generation of submicron emulsion droplets via highly stable tip-streaming mode in microfluidic devices. Lab Chip 2012, 12, 1446−1453. (29) Whitney, R. P.; Vivian, J. E. Solubility of chlorine in water. Ind. Eng. Chem. 1941, 33, 741−744. (30) Alkan, M.; Oktay, M.; Kocakerimc, M. M.; Copur, M. Solubility of chlorine in aqueous hydrochloric acid solutions. J. Hazard Mater. 2005, A119, 13−18. (31) Islam, M. A.; Kalam, M. A.; Khan, M. R. Reactive gas solubility in water: An empirical relation. Ind. Eng. Chem. Res. 2000, 39, 2627− 2630.
In the future, more work could be carried out, such as the kinetics of chlorohydrination, the mass transfer characteristic, and optimizing the operating conditions in the microsystem.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (Y.C.Lu);
[email protected]. cn (G.S.Luo). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully acknowledge the support of the National Natural Science Foundation of China (21036002, 21176136) and National Basic Research Program of China (2012CBA01203) for this work.
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REFERENCES
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dx.doi.org/10.1021/ie301816k | Ind. Eng. Chem. Res. 2012, 51, 14685−14691
