- Email: [email protected]
The epoxidation of allylchlorides with hydrogen peroxide over TS-1
Science and Technology in Catalysis 1998 Copyright © 1999 by Kodansha Ltd.
55 The Epoxidation of Allylchlorides with Hydrogen Peroxide over TS-1
Tomoyuki KITANO and Yasuo KIKUZONO Research Laboratories, Daiso Co., Ltd., 9, Otakasu-cho, Amagasaki-shi, 660-0842, Japan
Abstract The solvent effect of methanol, the improvement of epoxide selectivity by blocking acid site, the increase in the epoxidation rate with the irradiation of ultrasonic waves and the reactivation of a used catalyst for the title reaction were studied. (1) Methanol worked as an inhibitor for the epoxidation of 2- methylallyl chloride (MAC), but as an accelerator for that of the allyl chloride. (2) The acid site blocked with cations suppressed the hydrolysis of the epoxide into a diol compound, and increased the selectivity and the reaction rate. (3) The irradiation of ultrasonic waves in the reaction media increased both the reaction rate and selectivity. (4) The extraction with organic solvent during the ultrasonic wave irradiation indicated such a good performance for the reactivation of the used catalyst that the conversion of hydrogen peroxide (0.6 eq added vs. MAC) and the selectivity of MAC to the epoxide were 99.6%, and 93.5% , respectively, at 40 °C for 2 hours. 1. INTRODUCTION Epichlorohydrin, which is a bi-functional organic compound having a glycidyl group and a chlorine atom at the allyl position, is an important raw material in the polymer and rubber industries. It is synthesized by the dehydrochlorination of dichloropropanol derived from the reaction of allychloride with CI2 and H2O, which produces much waste water. Recent demand for an environmentally friendly process is strong. The titanosilicate compound is one of the promising catalysts for the epoxidation of olefins due to its environmental advantages associated with H2O2 as a clean oxidizing agent with high selectivity. In this paper, we discuss the title reaction. 2. EXPERIMENT TS-1 was crystallized from Ti02-Si02 gel using tetrapropylammonium hydroxide aqueous solution under an autogeneous pressure at 443 K for 24 hrs with stirring in an autoclave. The gel was synthesized with the hydrolysis of Ti(0-n-C4H9)4 and Si(OC2H5)4. The reaction was carried out under vigorous stirring at 317 K for 2 hrs in a 30 ml autoclave containing the TS-1 calcined at 823 K for 3 hrs, substrate olefin, 35 wt%-hydrogen peroxide aqueous solution and methanol if needed. All organic compounds were analyzed by GC and the concentration of hydrogen peroxide was titrated by iodometry.
355
356 T. Kitano^r«/.
3. RESULTS AND DISCUSSION 3.1 Effect of methanol Figure 1 indicates the effect of methanol on the catalytic epoxidation of 2-methylallyl chloride (MAC) and allylchloride (AC). Very different behavior was observed between them. Although methanol is required for AC to obtain high selectivity and high conversion, it acts as an inhibitor for MAC. Bhaumik et al. reported that the diffusion parameters of substrate and solvent through zeolite channels were significant especially for the hydroxylation of hydrophobic compounds [1] and also reported that AC was more easily dihydroxylized than MAC via the corresponding epoxide in TS-I/H2O2/H2O system [2]. These results suggested that steric hindrance through the channels, hydrophobicity/hydrophilicity of both substrate and epoxide, and their stability in the reaction media were important factors for the reaction. Although the detail mechanism is under investigation, the nonuse of methanol encourages us to develop a novel epoxidation process of MAC with TS-1 due to the advantages in product separation. Table 1. Effect of additives on the catalyst activities.
100
Additives none TIF TINO3 TlCl CsF
0
10
20 30 40 Conversion, %
50
60
Fig.l. Effect of methanol as a solvent square: H2O2 basis, round: substrate basis. Substrate; Full: MAC, empty: AC, Numbers in the Fig.: methanol (mmol), Reaction; TS-1: 0. Ig, substrate:68 mmol, H2O2:38 mmol, H20:138 mmol. Time:2h, Temp., 40'C.
CS2CO3 Na2C03 K2CO3
Conversion of MAC ,% 59.8 52.3 52.3 58.5 31.4 39.7 41.4 26.7
Selectivity of MAC to MEP,% 86.2 93.9 96.5 93.9 97.2 98.4 94.8 93.4
Selectivity of MAC to Diol, % 7.7 4.3 3.0 4.2 0.2 0 0.1 0
Reaction; TS-l;0.2g, MAC;18mmol, H202;l lmmol,H2O;60mmol Cation /(Si+Ti in TS-1): 15(atomic ratio). Time:2h, Temp., 40'C.
3.2 Suppression of the epoxide hydrolysis with Tl salts Patents [3,4] claimed that the addition of a neutralizing agent, such as Na2C03 and NFltOH, into the reaction media is effective for suppressing the hydrolysis of epoxide which induces the deactivation of the catalyst by the obstruction of the zeolite channels. The main reaction was suppressed as well as the side reaction, when the salts were applied. The results obtained for the epoxidation of MAC containing a series of T1(I) and alkali metal cations as the neutralizing agent are listed in Table 1. Only the Tl salts suppressed the hydrolysis of epoxide with high conversion of MAC. TIF was the most effective. We speculated that the results would be explained by the difference of hydrophobicity in the zeolite channels when replaced by Tl and Na cations. Since Tl has a larger ion diameter than Na, the hydrophobicity due to Tl would be kept with a small gradient of electric field.
357
3.3 Irradiation of ultrasonic wave (USW) Since molecular sizes of substrates and products are very close to the MFI zeolite channel (5.3 X 5.6 A ) , the rate-determining step would be their diffusion rates in the zeolite. To enhance the diffusion rate, the irradiation of USW on the reaction media was studied. The results obtained are listed in Table 2. The reaction was carried out in a 50-ml flask under atmospheric pressure, so the reaction rate was slightly slower than that in the figures. The irradiation of USW accelerated the reaction rate with increasing selectivity. When the USW energy became higher, the selectivity to the diol increased. The addition of ammonium carbonate was very efficient for not only suppression of the epoxide ring opening, but also acceleration of the epoxidation. The conversion of hydrogen peroxide was 99.6% for 2 hours with 78.4% selectivity. Table 2. Irradiation of ultrasonic wave (USW) on the reaction media. Selectivity of Selectivity of Selectivity of Reaction Conversion of USW MAC to MEP MAC to Diol hydrogen hydrogen time, h irradiation peroxide, % peroxide, % none 4 97.0 65.9 69.2 10.8 9.1 82.8 200W, 39kHz 2 97.4 81.1 60W, 45kHz 81.9 6.9 2 97.9 79.5 60W, 45kHz«) 99.6 78.4 93.5 0.4 2 Reaction time: 2 h. Stir rate: 200rpm , Temp.: 40''C, Cat: 2.0g, 35wt%-H202:10.4g (107mmol, 0.6eq vs MAC), MAC 16.2g (179mmol), a) 1.3wt%-(NH4)2C03 vs. TS-1. was added. 3.4 Reactivation of catalyst The catalyst activity decreased to half when a used catalyst was employed. The stacking of the polymeric compounds would be the reason for this decrease. The reactivation is very important for the catalyst system. Calcination and extraction under USW irradiation were studied. 3.4.1 Calcination When the calcination was carried out under 500 °C in air, the catalyst activity was not fully recovered. Over 550 °C was required. Figure 2 indicates the catalyst activity change during repeated calcination at 550°C. The selectivity and conversion for hydrogen peroxide decreased by 1% for each calcination. This method will not be employed as the only reactivating method for the used catalyst. 3.4.2 Extraction under ultrasonic wave The extraction of the organic compounds accumulated in zeolite channel with an organic solvent was studied as another reactivation method. When extraction using an organic solvent was carried out at its reflux temperature, the activity drastically decreased. The polymeric compounds might be accumulated in the zeolite channel during the extraction treatment. To avoid polymerization, extraction was carried out at 30 C under USW irradiation. The results obtained are illustrated in Fig. 3. Methanol recovered the conversion of hydrogen peroxide, but the selectivity decreased. Acetone was the prospective solvent. In order to use the catalyst repeatedly, the extraction under ultrasonic waves was a useful method for the reactivation of the used catalyst.
358 T.K'itano era!. 95 D
a
90 D
^
A
85 ^"^"•^--^.^^D
# 80
^
B
80
75 70
• 65 1
2
3
4 5 6 7 8 Recycle times
9
10
Fig. 2 Calcination for reactivation AiConversion of Hydrogen peroxide, B.Selectivity of hydrogen peroxide. Reaction; TS-1: O.lg, substrate:68 mmol, H2O2:38 mmol, HsOiBS mmol. 40"C, 2h Calcination: 5501C, 3h
New
MeOH CH2CI2 No extract Acetone Solvent
Fig. 3 Extraction during USW irradiation. Bars;dots:Selectivity of MAC to MEP, Oblique lines: Selectivity of HP, Snapped line: the conversion of HP, Reaction; TS-1: O.lg, substrate:68 mmol, H2O2:38 mmol, H20:138 mmol. 40°C, 2h USW:200W,39kHz, Ih
4. CONCLUSION Methanol produced very different behaviors for the epoxidation of the allyl chloride homologs with hydrogen peroxide over TS-1. It worked as an inhibitor for the epoxidation of MAC, but as an accelerator for that of AC. The epoxide hydrolysis was surpressed by blocking the acid site on the catalyst, producing high selectivity and a high epoxidation rate. These were further improved by irradiation with ultrasonic waves in the reaction media. The extraction with organic solvent during ultrasonic wave irradiation at a lower temperature was a useful way for reactivating used catalyst. Although calcination was useful for the reactivation, the selectivity of hydrogen peroxide decreased by 1% for each calcination. The conversion of hydrogen peroxide (0.6 eq added vs. MAC) and the selectivity of MAC to the epoxide were 99.6% and 93.5% , respectively, at 40 "C for 2 hours. References [1] A.BhaumikandR.Kumar, J.Chem.Soc, Chem.Commun, 349-350, 1995. [2] A.Bhaumik and T.Tatsumi J.Catal., 176, 305-309, 1998 [3] USP 4,824,976 (1989). [4] JP 96-225,556 (1996).
55 The Epoxidation of Allylchlorides with Hydrogen Peroxide over TS-1
Tomoyuki KITANO and Yasuo KIKUZONO Research Laboratories, Daiso Co., Ltd., 9, Otakasu-cho, Amagasaki-shi, 660-0842, Japan
Abstract The solvent effect of methanol, the improvement of epoxide selectivity by blocking acid site, the increase in the epoxidation rate with the irradiation of ultrasonic waves and the reactivation of a used catalyst for the title reaction were studied. (1) Methanol worked as an inhibitor for the epoxidation of 2- methylallyl chloride (MAC), but as an accelerator for that of the allyl chloride. (2) The acid site blocked with cations suppressed the hydrolysis of the epoxide into a diol compound, and increased the selectivity and the reaction rate. (3) The irradiation of ultrasonic waves in the reaction media increased both the reaction rate and selectivity. (4) The extraction with organic solvent during the ultrasonic wave irradiation indicated such a good performance for the reactivation of the used catalyst that the conversion of hydrogen peroxide (0.6 eq added vs. MAC) and the selectivity of MAC to the epoxide were 99.6%, and 93.5% , respectively, at 40 °C for 2 hours. 1. INTRODUCTION Epichlorohydrin, which is a bi-functional organic compound having a glycidyl group and a chlorine atom at the allyl position, is an important raw material in the polymer and rubber industries. It is synthesized by the dehydrochlorination of dichloropropanol derived from the reaction of allychloride with CI2 and H2O, which produces much waste water. Recent demand for an environmentally friendly process is strong. The titanosilicate compound is one of the promising catalysts for the epoxidation of olefins due to its environmental advantages associated with H2O2 as a clean oxidizing agent with high selectivity. In this paper, we discuss the title reaction. 2. EXPERIMENT TS-1 was crystallized from Ti02-Si02 gel using tetrapropylammonium hydroxide aqueous solution under an autogeneous pressure at 443 K for 24 hrs with stirring in an autoclave. The gel was synthesized with the hydrolysis of Ti(0-n-C4H9)4 and Si(OC2H5)4. The reaction was carried out under vigorous stirring at 317 K for 2 hrs in a 30 ml autoclave containing the TS-1 calcined at 823 K for 3 hrs, substrate olefin, 35 wt%-hydrogen peroxide aqueous solution and methanol if needed. All organic compounds were analyzed by GC and the concentration of hydrogen peroxide was titrated by iodometry.
355
356 T. Kitano^r«/.
3. RESULTS AND DISCUSSION 3.1 Effect of methanol Figure 1 indicates the effect of methanol on the catalytic epoxidation of 2-methylallyl chloride (MAC) and allylchloride (AC). Very different behavior was observed between them. Although methanol is required for AC to obtain high selectivity and high conversion, it acts as an inhibitor for MAC. Bhaumik et al. reported that the diffusion parameters of substrate and solvent through zeolite channels were significant especially for the hydroxylation of hydrophobic compounds [1] and also reported that AC was more easily dihydroxylized than MAC via the corresponding epoxide in TS-I/H2O2/H2O system [2]. These results suggested that steric hindrance through the channels, hydrophobicity/hydrophilicity of both substrate and epoxide, and their stability in the reaction media were important factors for the reaction. Although the detail mechanism is under investigation, the nonuse of methanol encourages us to develop a novel epoxidation process of MAC with TS-1 due to the advantages in product separation. Table 1. Effect of additives on the catalyst activities.
100
Additives none TIF TINO3 TlCl CsF
0
10
20 30 40 Conversion, %
50
60
Fig.l. Effect of methanol as a solvent square: H2O2 basis, round: substrate basis. Substrate; Full: MAC, empty: AC, Numbers in the Fig.: methanol (mmol), Reaction; TS-1: 0. Ig, substrate:68 mmol, H2O2:38 mmol, H20:138 mmol. Time:2h, Temp., 40'C.
CS2CO3 Na2C03 K2CO3
Conversion of MAC ,% 59.8 52.3 52.3 58.5 31.4 39.7 41.4 26.7
Selectivity of MAC to MEP,% 86.2 93.9 96.5 93.9 97.2 98.4 94.8 93.4
Selectivity of MAC to Diol, % 7.7 4.3 3.0 4.2 0.2 0 0.1 0
Reaction; TS-l;0.2g, MAC;18mmol, H202;l lmmol,H2O;60mmol Cation /(Si+Ti in TS-1): 15(atomic ratio). Time:2h, Temp., 40'C.
3.2 Suppression of the epoxide hydrolysis with Tl salts Patents [3,4] claimed that the addition of a neutralizing agent, such as Na2C03 and NFltOH, into the reaction media is effective for suppressing the hydrolysis of epoxide which induces the deactivation of the catalyst by the obstruction of the zeolite channels. The main reaction was suppressed as well as the side reaction, when the salts were applied. The results obtained for the epoxidation of MAC containing a series of T1(I) and alkali metal cations as the neutralizing agent are listed in Table 1. Only the Tl salts suppressed the hydrolysis of epoxide with high conversion of MAC. TIF was the most effective. We speculated that the results would be explained by the difference of hydrophobicity in the zeolite channels when replaced by Tl and Na cations. Since Tl has a larger ion diameter than Na, the hydrophobicity due to Tl would be kept with a small gradient of electric field.
357
3.3 Irradiation of ultrasonic wave (USW) Since molecular sizes of substrates and products are very close to the MFI zeolite channel (5.3 X 5.6 A ) , the rate-determining step would be their diffusion rates in the zeolite. To enhance the diffusion rate, the irradiation of USW on the reaction media was studied. The results obtained are listed in Table 2. The reaction was carried out in a 50-ml flask under atmospheric pressure, so the reaction rate was slightly slower than that in the figures. The irradiation of USW accelerated the reaction rate with increasing selectivity. When the USW energy became higher, the selectivity to the diol increased. The addition of ammonium carbonate was very efficient for not only suppression of the epoxide ring opening, but also acceleration of the epoxidation. The conversion of hydrogen peroxide was 99.6% for 2 hours with 78.4% selectivity. Table 2. Irradiation of ultrasonic wave (USW) on the reaction media. Selectivity of Selectivity of Selectivity of Reaction Conversion of USW MAC to MEP MAC to Diol hydrogen hydrogen time, h irradiation peroxide, % peroxide, % none 4 97.0 65.9 69.2 10.8 9.1 82.8 200W, 39kHz 2 97.4 81.1 60W, 45kHz 81.9 6.9 2 97.9 79.5 60W, 45kHz«) 99.6 78.4 93.5 0.4 2 Reaction time: 2 h. Stir rate: 200rpm , Temp.: 40''C, Cat: 2.0g, 35wt%-H202:10.4g (107mmol, 0.6eq vs MAC), MAC 16.2g (179mmol), a) 1.3wt%-(NH4)2C03 vs. TS-1. was added. 3.4 Reactivation of catalyst The catalyst activity decreased to half when a used catalyst was employed. The stacking of the polymeric compounds would be the reason for this decrease. The reactivation is very important for the catalyst system. Calcination and extraction under USW irradiation were studied. 3.4.1 Calcination When the calcination was carried out under 500 °C in air, the catalyst activity was not fully recovered. Over 550 °C was required. Figure 2 indicates the catalyst activity change during repeated calcination at 550°C. The selectivity and conversion for hydrogen peroxide decreased by 1% for each calcination. This method will not be employed as the only reactivating method for the used catalyst. 3.4.2 Extraction under ultrasonic wave The extraction of the organic compounds accumulated in zeolite channel with an organic solvent was studied as another reactivation method. When extraction using an organic solvent was carried out at its reflux temperature, the activity drastically decreased. The polymeric compounds might be accumulated in the zeolite channel during the extraction treatment. To avoid polymerization, extraction was carried out at 30 C under USW irradiation. The results obtained are illustrated in Fig. 3. Methanol recovered the conversion of hydrogen peroxide, but the selectivity decreased. Acetone was the prospective solvent. In order to use the catalyst repeatedly, the extraction under ultrasonic waves was a useful method for the reactivation of the used catalyst.
358 T.K'itano era!. 95 D
a
90 D
^
A
85 ^"^"•^--^.^^D
# 80
^
B
80
75 70
• 65 1
2
3
4 5 6 7 8 Recycle times
9
10
Fig. 2 Calcination for reactivation AiConversion of Hydrogen peroxide, B.Selectivity of hydrogen peroxide. Reaction; TS-1: O.lg, substrate:68 mmol, H2O2:38 mmol, HsOiBS mmol. 40"C, 2h Calcination: 5501C, 3h
New
MeOH CH2CI2 No extract Acetone Solvent
Fig. 3 Extraction during USW irradiation. Bars;dots:Selectivity of MAC to MEP, Oblique lines: Selectivity of HP, Snapped line: the conversion of HP, Reaction; TS-1: O.lg, substrate:68 mmol, H2O2:38 mmol, H20:138 mmol. 40°C, 2h USW:200W,39kHz, Ih
4. CONCLUSION Methanol produced very different behaviors for the epoxidation of the allyl chloride homologs with hydrogen peroxide over TS-1. It worked as an inhibitor for the epoxidation of MAC, but as an accelerator for that of AC. The epoxide hydrolysis was surpressed by blocking the acid site on the catalyst, producing high selectivity and a high epoxidation rate. These were further improved by irradiation with ultrasonic waves in the reaction media. The extraction with organic solvent during ultrasonic wave irradiation at a lower temperature was a useful way for reactivating used catalyst. Although calcination was useful for the reactivation, the selectivity of hydrogen peroxide decreased by 1% for each calcination. The conversion of hydrogen peroxide (0.6 eq added vs. MAC) and the selectivity of MAC to the epoxide were 99.6% and 93.5% , respectively, at 40 "C for 2 hours. References [1] A.BhaumikandR.Kumar, J.Chem.Soc, Chem.Commun, 349-350, 1995. [2] A.Bhaumik and T.Tatsumi J.Catal., 176, 305-309, 1998 [3] USP 4,824,976 (1989). [4] JP 96-225,556 (1996).