A Novel Route for Carbon Dioxide Cycloaddition to Propylene

Chapter 8 A Novel Route for Carbon Dioxide Cycloaddition

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to Propylene Carbonate W. Wei, Τ. Wei, and Y. Sun* State Key Laboratory of Coal Conservation, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

A combination of K J supported catalysts on different supports with a novel continual structural reactor for the production of propylene carbonate from CO2 cycloaddition was investigated in this paper. With neither solvents nor promoters in this synthesis, both propylene oxide conversion and propylene carbonate selectivity were nearly 100% at moderate conditions over the supported catalysts. In the structural reactor, the lifetime of the catalysts can be highly improved with a much higher yield of propylene carbonate, compared to that obtained from the conventional reactor.

Introduction The formation of a five-cyclic membered carbonate (such as propylene carbonate or ethylene carbonate) via cycloaddition between C 0 and epoxides (such as propylene oxide and ethylene oxide) is not only one of the routes for C 0 chemical fixation (/), but also is the first step for the synthesis of dimethyl carbonate (DMC) via transesterification (2). Furthermore, propylene carbonate (PC) or ethylene carbonate itself is a nontoxic and versatile intermediate in 2

2

130

© 2003 American Chemical Society

In Utilization of Greenhouse Gases; Liu, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


131 environmentally benign organic syntheses. In particular, alkylene carbonate is a colorless solvent with a relatively high dielectric constant. It is mainly used as a non-aqueous solvent for electrolytes in high-energy batteries. In addition, it is widely used in polycarbonate syntheses and used as an intermediate in pharmaceutical processes, as an oxyalkylation agent in dyestuff syntheses, and as a solvent in textile production processes. Hence, the green synthesis route of propylene carbonate or ethylene carbonate is expected in this half century. Nemirovsky first reported the synthesis of alkyl carbonate by phosgenation a century ago (5), but the method has gradually been abandoned because of the use toxic and hazardous phosgene. After the 1960s, many patents have been issued for the production of alkyl carbonate (4-11). Particularly, much attention has been paid to the cycloaddition between propylene oxide (PO) and C 0 . The main catalysts include organometallic halide-Lewis bases (i), organotin haldetetraalkyphosphonium halides (/), alkali metal halide-crown ethers (12) and polyethylene glycol-400 (13). But the catalytic performance and the severe reaction conditions limit their further utilization. In addition, a variety of solvents or promoters must be used, resulting in high separation costs or low purity of PC. Moreover, the reaction was carried out in an intermission autoclave, leading to a low production capacity. Thus, we have developed a new heterogeneous catalyst with high catalytic activity at moderate conditions (i.e., K I supported catalysts on various supports). In order to improve the lifetime and productivity of the catalysts and avoid the hot spot of die catalysts, a new continual structural reactor was investigated. Combining the new heterogeneous catalysts and the new continual structural reactor, a novel method for cycloaddition between PO and C 0 as a heterogeneous process was developed in the present work. 2

2

Experimental The purity of C 0 was higher than 99.5%. Commercially available PO or ethylene oxide (EO) was used without further purification. Catalysts were prepared by impregnating the supports with an aqueous solution of KI, and then dried at 60 °C for 10 h. A l l supports were commercially obtained. The catalysts were first evaluated in a conventional intermission autoclave. The cycloaddition between C 0 and PO is an intense exothermal reaction (AH«30kcal/mol), which leads to difficult operations of the heterogeneous catalytic process due to the higher local temperatures and the limitation of die lifetime of catalyst. Thus, a new structural reactor was designed. In this reactor the lifetime of the catalysts was significantly improved. 2

2


132

Results and Discussion


Activity of KI supported catalyst over different supports. In the heterogeneous process, K I supported on different supports was investigated (see Table 1). First, the reaction conditions (reaction temperature: 120 °C ; pressure: 4.0MPa) were moderate, and the pressure was lower than the saturate pressure of carbon dioxide at room temperature. Secondly, both PO conversion and PC selectivity were nearly 100% although neither solvents nor promoters were used. Thus, the product did not need to be separated, which simplified the production of PC. In addition, the yield of PC was much higher than that for the conventional heterogeneous process (< 5g/(g(cat.) · hr)). For activated carbon supported K I catalyst, the yield reached up to 12.0 g/(g(cat.) · hr).

Table I . Effect of supports on catalytic performance Catalysts

yield kg/(kz(cat)

PO Conversion

PCyield

%

%

100.0

99.0

7.0

ΚΙ/activated carbon

100.0

99.3

12.0

KI/SiO,

100.0

99.0

7.4

ΚΙ/γ-Α1 0 2

3

'hr)

NOTE: T=120°C, P=4.0MPa, C0 /PO(molar ratio)=3:l. 2

The structural properties of the catalysts The B E T surface areas of three catalysts are shown in Table 2. Among them, the surface area of the ΚΙ/activated carbon was the highest, and that of ΚΙ/γA 1 0 was the lowest. This might be the reason that the supports showed a strong influence. In addition, the acid site of both γ-Α1 0 and S i 0 also might suppress the reaction rate. The detail mechanism is under investigation. 2

3

2

3

2

Lifetime of ΚΙ/activated carbon In a 1-L conventional intermission autoclave, the catalytic activity of ΚΙ/activated carbon sharply decreased in 100 hours (see Figure 1 and Figure 2). The texture of fresh catalyst and after reaction catalyst greatly changed (see Table 3). Obviously, the fouling of the pores, especially the small pores, was


133 very severe in the reaction in the conventional intermission autoclave, which led to a great decrease in the surface area. In addition, color was observed in the product, indicating that the K I in the catalyst was partly oxidized during reaction. This occurred because the reaction heat could not be removed and thus produced local hot spots.

Table 2. The structural properties of the catalysts BET surface m /z

Average pore diameter Â

pore volume. cm /g

279.3

43.5

0.32

ΚΙ/activated carbon

394.3

22.2

0.22

KI/SiO,

329.4

79.8

0.64


Catalysts

2

ΚΙ/γ-Α1 0 2

3

40

60

3

80

Reaction time > h

Figure 1. Change of Ρ Ο conversion with reaction time in 1 L conventional intermission autoclave at 4MPa, 120 Vand 3:1 of C0 to PO molar ratio. 2



134

Φ

CO 30204

0

•

1

1

20

40

·

1

60

·

1

•

80

ι

100

reaction timet h Figure 2. Change of PC selectivity with reaction time in 1 L conventional intermission autoclave at 4MPa, 120 °C and 3:1 of C0 to Ρ Ο molar ratio. 2

Table 3. The structural properties of ΚΙ/activated carbon fresh and used catalysts Catalysts

BETsurface m /z 394.3 40.7 2

fresh catalyst used catalyst

Average pore diameter A 22.2 56.8

Pore volume. cm /g 0.22 0.06 3

In order to further improve the lifetime and productivity capability of the catalysts and avoid the hot spot in the catalysts, a novel continual structural reactor was designed (14). The structural schematic diagram of the reactor is showed in Figure 3. In the reactor the supported catalysts were loaded in the thin baskets that were especially placed. During the reaction, water or nitrogen or air, was introduced into the heat exchanger to remove reaction heat. Furthermore, the reaction system could be operated continually to enhance the productivity. This reactor has the following advantages: (1) PC could be removed from the surface of the catalysts as soon as it was produced; (2) The reaction heat could be efficiently removed. Thus, the lifetime of the catalyst could be improved; (3) the reaction was continual in this reactor, and its productivity was improved. As a result, the activity of catalysts in die new reactor was highly improved. For ΚΙ/activated carbon, both PO conversion and PC selectivity hardly decreased after 400 h of continually operation (see Figure 4 and Figure 5). No color in die product was observed. In addition, the structural properties of die catalyst did not change. Thus, in the new reactor die catalyst is stable.



135

Catalyst basket Heat exchanger

Condenser ^ Propylene carbonate Figure 3. The structural schematic diagram of the new reactor.

100H-*

d CL Ο

1 % c ο ο

ι ι ι ι ' ι ι—•—ι1

Ο

1

1

1

50 100 150 200 250 300 350 400 reaction time,

h

Figure 4. Change of PO conversion with reaction time in 20 L new continual structural reactor at 4MP a, 120 Vand 3:1 of C0 to PO molar ratio. 2



136

100 150 200 250 300 350 400

reaction time' h Figure 5. Change of PC selectivity with reaction time in 20 L new continual structural reactor at 4MPa, 120 V and 3:1 ofC0 to PO molar ratio 2

Conclusion A novel structural reactor containing catalyst baskets has been designed to immediately remove the reaction heat. A better performance has been thereby achieved, compared to the conventional reactor. For supported K I catalysts, both PO conversion and PC selectivity approached 100% at moderate conditions, and the space time yield of PC reached up to 12 g/(g(cat.) · hr).

Reference 1. 2. 3. 4. 5. 6. 7.

Nomura R., Kimura M . , Teshima S , etc., Bull. Chem. Soc. Jpn., 1982, 55, 3200-3208. Baba A., Nozaki T., Miki T., Bull. Chem. Soc. Jpn., 1987,60,1552-1558. Nemirovsky I., Prakt J. Chem., 1883, 28,439-442. Fumagalli, Carlo; Caprara, Giuseppe; Roffia, Paolo. United States Patent 4,009,183. Gregory A Kao; Jar-lin; Sheng; Ming N. United States Patent 4,224,223. Richard G.; Michaelson; Robert C.; Myers; Richard S. United States Patent 4,824,969. Shikata, Kazuo; Shigemune,Toshiaki. United States Patent 4,217,298.



137 8. Venturello, Carlo; D'Aloisio, Rino. United States Patent 4,226,778. 9. Robert M. United States Patent 4,931,571. 10. Hoon Sik; Jai Jun; Sang Deuk; Kun You; Hong Gon. United States Patent 6,156,909. 11. Scott J.; Clarence D.; Robert Α.; Lorenzo C.; Zhaozhong; Jose G.; Hye Kyung Cho. United States Patent 6,258,962. 12. Rokicji G. and Kuran W., Bull. Chem. Soc. Jpn., 1984,57,1662-1670. 13. Tang Z.Z, Chen Y., Qu Z.J., etc, J. Peterochem Technol. (China), 1996, 25, 409-412. 14. Sun, Y.; Chen, X.; Wei, W. China patent: 01108814.1,2001


A Novel Route for Carbon Dioxide Cycloaddition to Propylene

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