Synthesis of dimethyl carbonate from transesterification of ethylene carbonate with methanol using immobilized ionic liquid on commercial silica

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1 Koren J. Chem. Eng., 27(5), (2010) DOI: /s RAPID COMMUNICATION Synthesis of dimethyl crbonte from trnsesterifiction of ethylene crbonte with methnol using immobilized ionic liquid on commercil silic Kyung-Hoon Kim*, Dong-Woo Kim*, Cheol-Woong Kim**, Je-Cheon Koh**, nd De-Won Prk*, *Division of Chemicl Engineering, Pusn Ntionl University, Busn , Kore **Kore Reserch Institute of Chemicl Technology, Dejeon , Kore (Received 31 October 2009 ccepted 19 November 2009) Abstrct Ionic liquid immobilized on commercil silic ctlysts proved to be n effective heterogeneous ctlyst for the synthesis of dimethyl crbonte () from trnsesterifiction of ethylene crbonte (EC) with methnol. The immobilized 1-n-lkyl imidzolium hlide ionic liquid on commercil silic (RImX-CS) ws chrcterized by EA, BET, FT-IR, 13 C NMR nd 29 Si NMR. It ws found tht RImX-CS with longer lkyl chin length showed much better ctlytic ctivity. RImX-CS with chloride (Cl ) s the counter nion showed the best ctlytic ctivity. High temperture, high crbon dioxide pressure, nd longer rection time were fvorble for the rectivity of BuImBr-CS. The ctlyst cn be reused for the rection up to three consecutive runs without ny considerble loss of its initil ctivity. Key words: Dimethyl Crbonte, Ethylene Crbonte, Methnol, Immobiliztion, Ionic Liquid INTRODUCTION To whom correspondence should be ddressed. E-mil: dwprk@pusn.c.kr 1441 The synthesis of dimethyl crbonte () is one of the promising rections for the utiliztion of nturlly bundnt crbon dioxide, which is one of greenhouse gses. is chieving incresing importnce in the chemicl industry for its verstility s regent nd solvent, nd its non-toxicity for humn helth nd environment. It cn be effectively used s n environmentlly benign substitute for highly toxic phosgene nd dimethyl sulfte in crbonyltion nd methyltion rection, s monomer for severl types of polymers nd intermedite in the synthesis of phrmceuticl nd griculturl chemicls [1]. cn lso be used s n octne booster due to its high oxygen content [2]. Conventionlly, hs been synthesized by using phosgene nd methnol. Therefore, number of nontoxic synthetic processes hve been suggested: (1) oxidtive crbonyltion using CO, O 2 nd methnol (2) direct synthesis of from crbon dioxide nd methnol (3) trnsesterifiction of methnol with cyclic crbonte. However, the oxidtive crbonyltion of methnol suffers from low production rte, need for corrosion resistnt rectors, nd toxicity nd potentil explosion of CO. For the trnsesterifiction method, mny homogeneous nd heterogeneous ctlysts hve been developed, such s tertiry mines [3], lkli metl or lkli metl compounds [4]. Knifton nd Durnleu [5] used free orgnic phosphines supported on prtilly crosslinked polystyrene for the rection. Heterogeneous ctlysts such s lkli-treted zeolite [6,7], bsic metl oxides [8,9], nd hydrotlcite [10] were lso reported. However, with some of these ctlysts, ctivity or selectivity ws not so high. The use of ionic liquids s environmentlly benign medi for ctlytic processes or chemicl extrction hs become widely recognized nd ccepted [11]. Ionic liquids hve negligible vpor pressure, excellent therml stbility nd specil chrcteristics in comprison with conventionl orgnic nd inorgnic solvents. In the pst decde, there hs been incresing use of ionic liquids contining imidzolium nd its counter nions in mny reserch fields such s lterntive rection medi, seprtion science nd mteril synthesis [11]. Mny rections ctlyzed with ionic liquids nd showing high performnce hve been reported [12,13]. In prticulr, ionic liquids bsed on imidzolium ctions nd chloroluminte nions, such s 1-butyl-3-methylimidzolium luminium chloride ([BMIm] Cl/AlCl 3 ), hve ttrcted growing interest [14,15]. In our previous work [16-20], we studied the performnce of ionic liquid for the synthesis of cyclic crbonte from epoxide nd crbon dioxide. Recently, ionic liquid-bsed heterogeneous ctlysts hve been developed to synthesize cyclic crbonte nd they llow the combintion of the dvntges of both homogeneous ionic liquids nd heterogeneous ctlysts. Compred to pure Lewis cidic ionic liquids, such heterogeneous ctlysts show dditionl dvntges such s the reduction of the mount of ionic liquids employed nd esy seprtion, s well s recovery of ctlyst from the rection mixture, which is desirble economiclly, environmentlly nd industrilly. The immobiliztion of ionic liquids onto MCM-41 showed excellent ctivities for crbon dioxide insertion rections; however, the use of expensive pore-directing gents nd lrge mounts of orgnic solvents to remove the templtes mkes these ctlysts imprcticble for commercil scle-up [21]. Moreover, the ordering of the mesopores often decreses s result. These problems could be voided through the usge of low-cost nd highly efficient ctlysts by grfting ionic liquids onto commercil silic. We hve previously studied the synthesis of using unsupported ionic liquids [22-25]. In the present work, immobilized imidzolium slt ionic liquids on commercil silic were prepred nd exmined for the esterifiction of EC nd methnol. The effects of rection time, crbon dioxide pressure, rection temperture nd mount of ctlyst re discussed for better understnding of the rection mechnism. A recycle test of the immobilized ctlyst ws lso

2 1442 K.-H. Kim et l. Scheme 1. Preprtion step of RImX-CS. crried out. EXPERIMENTAL 1. Mteril Imidzole (Aldrich), 1-bromobutne (Aldrich), 1-chlorobutne (Aldrich), 1-bromopropne (Aldrich), bromoethne (Aldrich), 1- iodobutne (Aldrich), (3-chloropropyl) triethoxysiline (Sigm), toluene (Aldrich), cetonitrile (De Jung), zinc choloride (Sigm), dicholoromethne (De Jung) nd llyl glycidyl ether (Aldrich) were used s received. A commercil silic gel (surfce re=500 m 2 /g, verge pore size=60 Å) ws purchsed from Aldrich nd purified using hot Pirnh solution (H 2 O 2 nd H 2 SO 4 ) before use. 2. Synthesis of RImX-CS 1-Alkyl-3-(3-triethoxysilylpropyl) imidzolium hlide (RImX) ws prepred using the procedure shown in Scheme 1. In typicl procedure, imidzole (3.4 g) ws dded in the flsk contining 50 ml dry toluene, (3-chloropyl) triethoxysiline (12 ml) ws poured into the solution nd the mixture ws refluxed for 3 h under rgon tmosphere. When the rection ws completed, 10 ml of 1-bromobutne ws subsequently injected into the flsk. The mixture ws kept stirred for nother 24 h; RImX cn be obtined fter removl of solvent. Following the similr procedures, RImX of different lkyl groups nd counter nions were synthesized by using 1-cholobutne, 1-bromopropne, bromoethne nd 1-iodobutne to replce 1-bromobutne, respectively. Synthesis of RImX grfted to commercil silic (RImX-CS) ws crried out s shown in Scheme 1. Prior to immobiliztion, commercil silic ws purified with hot Pirnh solution (H 2 O 2 nd H 2 SO 4 ) followed by rinsing in wter nd drying under strem of nitrogen. The pretreted silic nd ionic liquid were co-dispersed in nhydrous toluene in flsk. The mixture ws refluxed for 24 h under nitrogen tmosphere. The resultnt product ws filtered nd wshed with dichloromethne to remove excess ionic liquid. After evporting the residul solvent in vcuum oven, RImX-CS ws obtined. Scheme 2. Synthesis of from EC nd methnol. 3. Synthesis of The trnsesterifiction rection ws crried out in 50 ml stinless steel utoclve equipped with mgnetic stirrer. For ech typicl rection, RImX-CS ctlyst (0.2 g), EC (25 mmol) nd excess methnol (200 mmol) were chrged into the rector, nd the CO 2 ws introduced t room temperture to preset pressure. The rection ws strted by stirring when the desired temperture nd pressure were ttined. The rection ws performed in btch opertion mode. The nlysis of the products nd rectnts ws performed by using gs chromtogrph (HP 6890N) equipped with n FID nd cpillry column (HP-5, 5% phenyl methyl siloxne). Selectivities to nd EG re clculted on the bsis of EC s limited rectnt. 4. Chrcteriztion The elementl nlysis (EA) ws operted using Vrio EL III. 2 mg of the smples ws subjected to 1,100 o C nd sulfnilic cid ws used s stndrd. Solid-stte NMR ws crried out with 29 Si nd 13 C frequencies of 79.5, MHz, respectively, on INOVA- 400 WB MAS probe. 29 Si MAS spectr were mesured t room temperture with the following conditions: mgic-ngle spinning t 5 khz; π/2 pulse, 6.5 µs nd repetition dely of 60 s; 3928 scns which referenced to tetrmethylsilne. 13 C cross-polriztion spectr were mesured with recycle dely of 5 s, 1024 scns with the following conditions: mgic-ngle spinning t 5 khz; π/2 pulse, 7 µs. The spectr were referenced to tetrmethylsilne. RESULTS AND DISCUSSION 1. Chrcteriztion of Ctlysts 1-1. Elementl Anlysis (EA) Results The mount of grfted RImX ws determined by mens of EA. To get mximum grfting mount of RImX, n effective lterntive is to control the employed mount of RImX in the grfting rection process. According to our previous work [26] on the optimiztion of the mount of employed, 5 mmol of RImX per grm silic ws used. The corresponding grfted mounts of RImX determined by EA re summrized in Tble Si nd 13 C MAS-NMR Chrcteriztion To investigte the efficiency of grfting rection, solid-stte 29 Si MAS-NMR nlysis of BuImBr-CS ws crried out. As shown in Fig. 1, two peks re centered t 93 nd 103 ppm corresponding to Q 3 (Si (OSi) 3 (OH)) nd Q 4 (Si (OSi) 4 ) silicon toms, respectively. The peks situted t 61.9, 50.3 nd 42.2 ppm re ssigned to the T 3 (Si (OSi) 3 R), T 2 (Si (OSi) 2 R (OH)) nd T 1 (Si (OSi) R (OH) 2 ) orgnosilioxne, which indictes the presence of orgnic functionliztion moieties s the prt of the silic. Fig. 2 shows the 13 C MAS-NMR spectrum of BuImBr-CS. The chemicl shifts t 135 nd 150 ppm correspond to the three imid- Tble 1. EA nd grfting mount of RImX in different RImX-CSs Ctlyst N H C Amount of RImX (mmol/g-ct) 1 BuImCl-CS BuImBr-CS BuImI-CS EtImBr-CS September, 2010

3 Synthesis of from trnsesterifiction of EC with methnol using immobilized ionic liquid on commercil silic 1443 Fig. 1. Solid-stte 29 Si MAS-NMR spectr of BuImBr-CS. Fig. 3. Effect of rection time on the synthesis of from EC nd methnol (Rection conditions: EC=25 mmol, MeOH= 200 mmol, T=160 o C, P CO2 =1.34 MP). Fig C CP MAS NMR spectr of the BuImBr-CS. Fig. 4. Effect of rection temperture on the synthesis of from EC nd methnol (Rection conditions: EC=25 mmol, MeOH=200 mmol, rection time=6 h, P CO2 =1.34 MP). zole ring crbon toms. The signl t 65 ppm is ttributed to the crbon toms connecting on imidzole ring nd other crbon toms give peks from 25 to 47 ppm. 2. Rectivity Test in the Synthesis of from EC nd Methnol The synthesis of from the trnsesterifiction of EC nd methnol ws crried out in high-pressure btch rector using the heterogeneous RImX-CS ctlysts. nd EG were min products of the trnsesterifiction rection. Dimethyl ether nd glycol monoethyl ether were byproducts, nd smll peks of ethylene oxide from the decomposition of EC could be detected t longer rection time nd t high temperture. Fig. 3 shows time vrint conversion of EC nd yield of nd EG t 160 o C with BuImBr-CS ctlyst under initil CO 2 pressure of 1.34 MP. As the rection time proceeded, the conversion of EC incresed up to 6 h, nd then it remined nerly constnt. It ws reported tht the rection time needed to rrive t equilibrium depended highly on the type of ctlysts [27]. LiOH, KOH nd K 2 CO 3 ctlysts reched equilibrium in less thn 1 h; however, KBr nd KI rrived t equilibrium fter more thn 6 h. The yield of nd EG lso incresed up to 6 h, but the yield of ws higher thn tht of EG. According to mechnism proposed by Fng nd Xio [28], ws produced vi severl rection steps involving the formtion of CH 3 O nd its rection with EC. Ethylene glycol (EG) ws suggested to form by the rection of methnol nd the by-product intermedite produced in the step of synthesis. Therefore, the lower selectivity of EG cn be explined by lower rection rte of this consecutive rection. The trnsesterifiction of EC nd methnol ws performed t different tempertures in the rnge of o C nd the results re shown in Fig. 4. The conversion of EC nd product yield incresed s temperture incresed from 120 o C to 160 o C. However, EC conversion decresed t 180 o C probbly due to the prtil decomposition of the to EC for the long rection time t high temperture. Koren J. Chem. Eng.(Vol. 27, No. 5)

4 1444 K.-H. Kim et l. Tble 2. Effect of pressure on the synthesis of from EC nd methnol I.P. (MP) yield Rection conditions: EC=25 mmol, MeOH=200 mmol, ctlyst= BuImBr-CS, T=160 o C, time=6 h Tble 3. EC conversion nd selectivity for different mount of ctlysts Ctlysts Amount Tble 2 shows the effect of CO 2 pressure on the rectivity of the BuImBr-CS ctlyst. The yield of nd EG t 160 o C incresed s the initil CO 2 pressure incresed from 0.11 to 1.34 MP. CO 2 is not rectnt for the trnsesterifiction of EC nd methnol. However, high CO 2 pressure could inhibit the decomposition of EC to ethylene oxide nd CO 2. Erlier studies reported tht pressure hs positive role in the synthesis of cyclic crbontes from CO 2 nd epoxides [8,29,30]. The dependence of the rection on the mount of ctlyst used ws investigted. As shown in Tble 3, the EC conversion nd the yield of nd EG incresed when the mount of BuImBr-CS ctlyst incresed from 0.10 to 0.20 g. BuImBr-CS ctlyst hving the sme mount of immobilized BuImBr showed higher rectivity thn the soluble BuImBr ctlyst since the immobilized ctlyst hs more fvorble micro environment inside the pores. To investigte the effect of ionic liquid structure in the trnsesterifiction of EC nd methnol, RImX-CS of different lkyl groups nd counter nions were exmined nd the results re shown in Tble 4. From runs 2 nd 4, it is observed tht EC conversions nd TON of incresed with incresing lkyl chin length of the grfted RImXs. These results re in greement with the previous reports September, 2010 yield 1 BuImBr-CS 0.10 g BuImBr-CS 0.20 g BMImBr mmol time=6 h, P CO2 =1.34 MP Homogeneous BMImBr with the sme mount of ionic liquid s tht in 0.2 g of BuImBr-CS Tble 4. Effect of ionic liquid structure on the synthesis of from EC nd methnol Ctlysts yield TON of 1 BuImCl-CS BuImBr-CS BuImI-CS EtImBr-CS rection time=4 h, P CO2 =1.34 MP TON=(mole of )/(mole of RImX) Tble 5. EC conversion nd yield of nd EG for recycle test using BuImCl-CS yield on the effects of lkyl chin length [31,32]. It could be explined tht incresing the bulkiness of the lkyl chin, which forces the hlide ions wy from the ction esier, results in less electrosttic interction between nion nd ction nd consequently increses the vilbility of the nion. It is generlly known tht the type of nion of ionic liquid hs significnt effects on the ctlytic performnce of ionic liquids [33,34]. RImXs with different hlide nions, Cl (BuImCl-CS), Br (BuImBr- CS) nd I (BuImI-CS) were used to ctlyze the trnsesterifiction rection between EC nd methnol. As shown in runs 1, 2, nd 3, the TON of decresed in the order of BuImCl-CS (143.0)> BuImBr-CS (89.3)>BuImI-CS (87.8). Nucleophilicity nd steric hindrnce re both in the order I >Br >Cl [14]. These two conflicting fctors my influence the interction of the nion with crbon tom of CO 2. In this rection, the effect of steric hindrnce seems to be dominnt to tht of nucleophilicity of the nions. Recycling experiments were crried out to investigte the stbility of the immobilized ionic liquid ctlyst. In ech cycle, the ctlyst ws seprted by filtrtion nd then used directly for the next run without regenertion or ddition of BuImBr-CS ctlyst. Tble 5 shows the ctivity of the reused BuImBr-CS ctlyst. The weight of recovered ctlyst decresed little due to the filtrtion step. The conversion of EC nd the yield of lso decresed slightly fter three consecutive runs. However, the TON of even incresed during the recycle experiments. It mens tht the ctlyst cn be reused t lest up to three consecutive times without ny considerble loss of its initil ctivity. CONCLUSION In the synthesis of from EC nd methnol, the immobilized ionic liquid on commercil silic (RImX-CS) showed good ctlytic ctivity without using ny solvent. It ws found tht RImX- CS with longer lkyl chin length showed much better ctlytic ctivity. RImX-CS with chloride (Cl ) s the counter nion showed the best ctlytic ctivity mong RImX-CS ctlysts with different counter nions. High temperture, long rection time, nd high CO 2 pressure lso incresed the ctlytic ctivity. The BuImBr-CS cn be esily recovered nd reused without ny considerble loss of its initil ctivity. ACKNOWLEDGEMENTS TON of Fresh (0.2 g) st (0.18 g) nd (0.168 g) rd (0.155 g) rection time=6 h, P CO2 =1.34 MP TON=(mole of )/(mole of RImX) This study ws supported by Pusn Ntionl University Post-

5 Synthesis of from trnsesterifiction of EC with methnol using immobilized ionic liquid on commercil silic 1445 Doc. progrm, KBSI nd the Ministry of Environment s The Ecotechnopi 21 project. REFERENCES 1. Y. Ono, Appl. Ctl. A. Gen., 155, 133 (1997). 2. A. A. Shikh nd S. Sivrm, Chem. Rev., 96, 951 (1996). 3. U. Romno nd U. Melis, US Ptent, 4,062,884 (1977). 4. B. S. Ahn, B. G. Lee, H. S. Kim nd M. S. Hn, Rect. Kinet. Ctl. Lett., 73, 33 (2001). 5. J. F. Knifton nd R. G. Durnleu, J. Mol. Ctl., 67, 389 (1991). 6. T. Kondoh, Y. Okd, F. Tnk, S. Asok nd S. Ymnoto, US Ptent, 5,436,362 (1995). 7. T. Ttsumi, Y. Wtnbe nd K. A. Koyno, Chem. Commun., 2281 (1996). 8. B. M. Bhnge, S. Fujit, Y. Ikushim nd M. Ari, Appl. Ctl. A. Gen., 219, 259 (2001). 9. H. Abimnyu, K. S. Yoo, D. J. Moon, B. S. Ahn nd J. W. Song, J. Ind. Eng. Chem., 11, 502 (2005). 10. Y. Wtnbe nd T. Ttsumi, Micropor. Mesopor. Mter., 22, 399 (1998). 11. T. Welton, Chem. Rev., 99, 2071 (1999). 12. C. E. Song, W. H. Shim, E. J. Roh nd J. H. Choi, Chem. Commun., 1695 (2000). 13. S. Zhng, Y. Chen, F. Li, X. Lu, W. Di nd R. Mori, Ctl. Tody, 115, 61 (2006). 14. K. R. Seddon, Kinet. Ctl., 37, 693 (1996). 15. A. S. Lrsen, J. D. Holbery, F. S. Thm nd C. A. J. Reed, J. Am. Chem. Soc., 122, 7264 (2000). 16. D. W. Prk, N. Y. Moon, K. H. Kim, I. Kim nd S. W. Prk, Ctl. Tody, 115, 130 (2006). 17. E. H. Lee, S. W. Ch, M. D. Mnju, Y. Choe, J. Y. Ahn nd D. W. Prk, Koren J. Chem. Eng., 24, 547 (2007). 18. E. H. Lee, J. Y. Ahn, M. D. Mnju, D. W. Prk, S. W. Prk nd I. Kim, Ctl. Tody, 131, 130 (2008). 19. H. Y. Ju, M. D. Mnju, K. H. Kim, S. W. Prk nd D. W. Prk, J. Ind. Eng. Chem., 14, 157 (2008). 20. H. Y. Ju, J. Y. Ahn, M. D. Mnju, K. H. Kim nd D. W. Prk, Koren J. Chem. Eng., 25, 471 (2008). 21. S. Udykumr, H. L. Shim, M. K. Lee, S. W. Prk nd D. W. Prk, Ctl. Commun., 10, 659 (2009). 22. E. S. Jeong, K. H. Kim, D. W. Prk, S. W. Prk nd J. W. Lee, Rect. Kinet. Ctl. Lett., 86, 241 (2005). 23. H. Y. Ju, M. D. Mnju, D. W. Prk, Y. Choe nd S. W. Prk, Rect. Kinet. Ctl. Lett., 90, 3 (2007). 24. H. Y. Ju, M. D. Mnju, K. H. Kim, S. W. Prk nd D. W. Prk, Koren J. Chem. Eng., 24, 917 (2007). 25. D. W. Prk, E. S. Jeong, K. H. Kim, K. V. Bineesh, J. W. Lee nd S. W. Prk, Stud. Surf. Sci. Ctl., 159, 329 (2006). 26. L. Hn, S. W. Prk nd D. W. Prk, Energy Environ. Sci., DOI: /b910763k (2009). 27. B. S. Ahn, B. G. Lee, H. S. Kim nd M. S. Hn, Proc. 10 th APCChE, Oct., Kitkyushu, Jpn (2004). 28. Y. Fng nd W. Xio, Sepn. Puri. Technol., 34, 255 (2004). 29. B. M. Bhnge, S. Fujit, Y. Ikushim, K. Torii nd M. Ari, Green Chem., 5, 71 (2003). 30. J. Sun, S. I. Fujit, F. Zho nd M. Ari, Appl. Ctl. A: Gen., 287, 221 (2005). 31. H. Kwnmi, A. Sski, K. Mtsui nd Y. Ikushim, Chem. Commun., 7, 896 (2003). 32. J. Sun, L. Wng, S. Zhng, Z. Li, X. Zhng, W. Di nd R. Mori, J. Mol. Ctl. A, 256, 295 (2006). 33. D. J. Drensbourg nd M. W. Holtcmp, Coord. Chem. Rev., 153, 155 (1996). 34. T. Skkur, J. C. Choi nd H. Ysud, Chem. Rev., 107, 2365 (2007). Koren J. Chem. Eng.(Vol. 27, No. 5)

Morphology characterization. (a), SEM image of PS template nanospheres showing

Morphology characterization. (a), SEM image of PS template nanospheres showing b Supplementry Figure 1 Morphology chrcteriztion. (), SEM imge of PS templte nnospheres showing mono-dispersed sphericl shpe with pproximtely 200 nm in dimeter. The scle br is 500 nm. (b), SEM imge of