Dechlorination of Chloroprene Rubber by Coliquefaction with Natural

1986

Energy & Fuels 2008, 22, 1986–1990

Dechlorination of Chloroprene Rubber by Coliquefaction with Natural Rubber Containing Zinc Oxide Motoyuki Sugano,*,†,‡ Masafumi Tsubosaka,† Seiko Shimizu,† Masaharu Fujita,§ Tsutomu Fukumoto,§ Katsumi Hirano,† and Kiyoshi Mashimo† Department of Materials and Applied Chemistry, College of Science and Technology, Nihon UniVersity, 1-8, Kanda Surugadai, Chiyoda-ku, Tokyo, 101-8308, Japan, Department of Applied Chemistry, Junior College at Funabashi Campus, Nihon UniVersity, 7-24-1, Narashinodai, Funabashi, Chiba 274-8501, Japan, and Yamashita Rubber Co. Ltd., 1239, Kamekubo, Fujimino, Saitama, 356-8556, Japan ReceiVed December 5, 2007. ReVised Manuscript ReceiVed March 17, 2008

The coliquefaction of chloroprene rubber (CR) and natural rubber (NR) was carried out at 300-420 °C with pressurized nitrogen gas and decalin as a solvent. Upon coliquefaction, ZnO in both NR and CR is expected to capture chlorine from CR. As a result, in comparison to the individual liquefactions of CR and NR, the increase of the captured amount of chlorine by zinc and the synergistic effects of the upgrading reaction, such as the increase of oil (hexane-soluble constituent) yield, were observed upon coliquefaction of CR and NR. These enhancements were not observed after the liquefaction of CR with ZnO addition. Therefore, it was considered that the temperature range of dispersion of ZnO from NR into the reactant was close to the temperature range of the formation of HCl from CR. Further, it was also anticipated that the stabilization of radicals from both CR and NR was enhanced by the coliquefaction. The alicyclic solvent, decalin, which swelled CR and NR very well, was the most suitable solvent upon coliquefaction. The effects of vulcanization and carbon-black additive in both CR and NR were negligible on coliquefaction.

The chloroprene rubber (CR) is widely used in products such as suspension, engine mount, and tubes in automobiles. However, most of waste CR is landfilled because of the difficulty of reusing waste CR. The reuse of waste CR with the virgin CR produces material with reduced property values, such as strength and durability. Because of the reduction of filled-up land, the effective use of waste CR is necessary. The direct thermal recovery process of CR is not suitable because chlorinecontaining gas, such as HCl, evolved. Therefore, the liquefaction process of waste CR is required. However, little has been published concerning the liquefaction of CR, except for the pyrolysis of CR in a fluidized-bed reactor,1 because the chlorinecontaining gas also evolved on the liquefaction process of CR alone. Therefore, constructing the process to obtain chlorinefree oil from CR is necessary. One of the recovery processes of chlorine in poly(vinyl chloride) (PVC), liquefaction of PVC with metal sorbents, such as lime,2 Fe,3 Zn,3 Ca/Zn carbonate,3 CuO,3,4 TiO2,3 Co3O4,4 MgO,4 iron oxides,5,6 red mud,7 carbon composites of Ca,8 and

Fe-Ca,9 Al-Zn,10 and Al-Mg11 composites, was reported. On these liquefactions, chlorine in PVC was stabilized as metal chloride after the evolved HCl was reacted with the added metal sorbents. In comparison to the liquefaction of PVC in the absence of solvent, the yield of the residue decreased and the yield of oil increased significantly on the liquefaction with either decalin or tetralin as a solvent.12 In comparison to the physical structure of PVC, that of a rubber material is more complicated because of its three-dimensional cross-linked coil structure. Therefore, in this study, solvent is considered to be necessary for the liquefaction of rubber material. It is well-known that ZnO is contained in rubber products as a vulcanization activator. However, the amount of ZnO contained in CR is insufficient for consuming all of the chlorine in CR. Therefore, in this study, coliquefaction of CR and natural rubber (NR) was carried out at 300-420 °C with pressurized nitrogen gas and decalin as a solvent. Upon coliquefaction, ZnO contained in both CR and NR is expected to capture chlorine in CR. The purpose of this study is to obtain chlorine-free oil

* To whom correspondence should be addressed. Telephone: +81-33259-0809. Fax: +81-3-3293-7572. E-mail: [email protected]. † College of Science and Technology, Nihon University. ‡ Junior College at Funabashi Campus, Nihon University. § Yamashita Rubber Co. Ltd. (1) Kaminsky, W.; Mennerich, C.; Andersson, J. T.; Gotting, S. Polym. Degrad. Stab. 2000, 71, 39–51. (2) Kaminsky, W.; Schlesselmann, B.; Simon, C. M. Polym. Degrad. Stab. 1996, 53, 189–197. (3) Blazso´, M.; Jakab, E. J. Anal. Appl. Pyrolysis 1999, 49, 125–143. (4) Horikawa, S.; Takai, Y.; Ukei, H.; Azuma, N.; Ueno, A. J. Anal. Appl. Pyrolysis 1999, 51, 167–179. (5) Uddin, M. A.; Sakata, Y.; Shiraga, Y.; Muto, A.; Murata, K. Ind. Eng. Chem. Res. 1999, 38, 1406–1410.

(6) Kakuta, Y.; Hirano, K.; Sugano, M.; Mashimo, K. Waste Manage. 2008, 28, 615–621. (7) Yanik, J.; Uddin, M. A.; Sakata, Y. Energy Fuels 2001, 15, 163– 169. (8) Bhaskar, T.; Uddin, M. A.; Kaneko, J.; Kusaba, T.; Matsui, T.; Muto, A.; Sakata, Y.; Murata, K. Energy Fuels 2003, 17, 75–80. (9) Matsui, T.; Okita, T.; Fujii, Y.; Hakata, T.; Imai, T.; Bhaskar, T.; Sakata, Y. Appl. Catal., A 2004, 261, 135–141. (10) Tang, C.; Wang, Y.-Z.; Zhou, Q.; Zheng, L. Polym. Degrad. Stab. 2003, 81, 89–94. (11) Zhou, Q.; Tang, C.; Wang, Y.-Z.; Zheng, L. Fuel 2004, 83, 1727– 1732. (12) Kamo, T.; Kondo, Y.; Kodera, Y.; Sato, Y.; Kushiyama, S. Polym. Degrad. Stab. 2003, 81, 187–196.

Introduction

10.1021/ef700733e CCC: $40.75  2008 American Chemical Society Published on Web 05/03/2008

Dechlorination of CR by Coliquefaction with NR

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Figure 1. Experimental scheme for coliquefaction of CR and NR.

effectively by coliquefaction. The effects of liquefaction temperature, mixing ratio of NR, ZnO addition instead of NR, kind of solvent, and vulcanization with carbon-black addition are also discussed in this study. Experimental Section Samples. The unvulcanized samples of NR (ZnO content, 28.8%) and CR (ZnO content, 12.6%; Cl content, 19.5%) were supplied by the Yamashita Rubber Co. Ltd. The vulcanized samples of NR and CR were prepared with carbon black at the Yamashita Rubber Co. Ltd., and these samples were abbreviated as VNRC and VCRC, respectively. The contents of carbon black and sulfur in VNRC and VCRC were 17 and 2%, respectively. These samples were divided into small pieces, in which the size was within 0.010 × 0.010 × 0.005 m. These divided samples were dried for 1 h under vacuum at 20 °C before use. Coliquefaction. The experimental scheme for the coliquefaction process described below is summarized in Figure 1. The predetermined proportion (sum of the weight, 10 g) of NR and CR with decalin (15 g) as a solvent was placed in a 100 cm3 autoclave with a magnetic drive agitator. The feed amounts of NR and CR were prepared so that the atomic ratio of Zn/Cl in the mixture of NR and CR will be 1:1. After the autoclave was sealed, the air inside was replaced with N2 gas and the autoclave was pressurized with 2.0 MPa of N2 gas. The autoclave was heated to the predetermined temperature (300-420 °C) in an external electric furnace, and the coliquefaction process was maintained at the temperature for 60 min. After the coliquefaction process was finished, the autoclave was air-cooled and the gaseous products (gas) were collected in a Tedlar bag and analyzed. The product remaining in the autoclave was extracted with toluene under an ultrasonic irradiation. The tolueneinsoluble (residue) material was prepared from the residue by drying for 3 h under vacuum at 110 °C. The residue material was further extracted with water to separate the water-soluble (WS) and -insoluble (WI) constituents. After the toluene was evaporated from the filtrate, the toluene-soluble material was further extracted with n-hexane under an ultrasonic irradiation. The n-hexane-insoluble but toluene-soluble (asphaltene) material was obtained from the residue by drying for 3 h under vacuum at 60 °C. The n-hexane was evaporated from the filtrate, leaving the n-hexane-soluble (oil) material, yielding two kinds of fractions [180 -350 °C and 350-final boiling point (FBP)]. These were calculated from the proportion of these fractions in the oil constituent using the

simulated distillation gas chromatography (GC). Therefore, the yield of fraction [initial boiling point (IBP)-180 °C] in the oil constituent was calculated from the difference between the weight of the feed sample and that of the recovered constituents [gas and oil (180-350 °C), oil (350-FBP), asphaltene, and residue] on a daf basis. The individual liquefactions of NR and CR were carried out in a similar manner. All reactions were carried out in duplicate, and the experimental error was within 2%. Analysis. The gas chromatographic analyses of gaseous components (CH4, C2H6, C3H8, C4H10, CO, and CO2) collected after the liquefaction were performed on a Shimadzu GC-9A instrument equipped with a thermal conductivity detector and dual-column molecular sieve (7 m, Shimadzu) and Porapak N (2 m, Waters). The qualitative analyses of HCl and the chlorine-containing organic volatiles (vinyl chloride, methylene chloride, trichloroethylene, and chlorobenzene) were performed using a gas detector tube system (GASTEC). The simulated distillation GC analyses of the oil materials obtained after the liquefaction were performed on a Shimadzu GC14B instrument equipped with a flame ionization detector and a packed column (7 m, Shimadzu) filled with silica support and OV-1. The chlorine content in WS constituent was directly quantified by ion chromatography. After decalin was evaporated from the oil material, the heavy oil constituent (280-FBP) was obtained because the range of the boiling point of the heavy oil constituent was above 280 °C. A portion of any one of oil (280-FBP), asphaltene, and WI constituents was burned at 1030 °C and absorbed by a NaOH aqueous solution containing 3% H2O2. The chlorine present in the solution was also quantified by ion chromatography. The chlorine contents in the constituents of WI and WS were represented as water-insoluble chlorine (organic chloride) and water-soluble chlorine (inorganic chloride), respectively. The difference between the chlorine content in CR and the sum of the chlorine contents in the products [oil (280-FBP), asphaltene, WS, and WI] was estimated as chlorine in the volatiles, such as the vaporized HCl and the other gaseous and volatile components.

Results and Discussion Effects of Liquefaction Temperature on the Individual Liquefaction of the Unvulcanized Rubber Samples. The individual liquefactions of the unvulcanized rubber samples (NR and CR), which contained only ZnO as an additive, were carried out. The product yields and the chlorine distributions after the

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Figure 4. Effects of the mixing ratio of NR on the product yields after the coliquefaction of NR and CR at 360 °C.

Figure 2. Product yields after the individual liquefaction and coliquefaction of NR and CR at various liquefaction temperatures.

organic radicals because the amount of ZnO in CR was insufficient for the stabilization of chlorine in CR. Effects of the Liquefaction Temperature on Coliquefaction of the Unvulcanized Rubber Samples. The product yields and the chlorine distributions after the coliquefaction of NR and CR with various liquefaction temperatures were also shown in Figures 2 and 3, respectively. The calculated yields13 of the coliquefaction were estimated from the product yields (Figure 2) of the individual liquefaction based on the feed amounts of NR and CR upon coliquefaction using eq 1 calculated yield (%) ) YN

Figure 3. Chlorine distributions after the individual liquefaction and coliquefaction of NR and CR at various liquefaction temperatures.

individual liquefaction of NR and CR at various liquefaction temperatures were shown in Figures 2 and 3, respectively. From Figure 2, upon liquefaction of NR alone, over 99% of NR was converted into the oil constituent even at the liquefaction temperature of 300 °C. On the other hand, upon liquefaction of CR alone, the yield of residue was very high and increased with the increase of the liquefaction temperatures. Therefore, it was expected that the cross-linking reaction among the radicals derived from the cleavage of the C-Cl bond in molecules of CR occurred, which resulted in high residue yields. From Figure 3, upon liquefaction of CR alone, 56% of chlorine in CR was contained in the WS constituent, meaning 40% of chlorine in CR was converted to the volatile constituent. After the liquefaction of CR alone, the chlorine-containing organic volatiles were detected using a gas detector tube system. In other words, 56% of chlorine in CR reacted with ZnO in CR to form ZnCl2 contained in the WS constituent; however, 40% of chlorine in CR formed the vaporized HCl or reacted with the gaseous or volatile organic radicals. The atomic ratio of Zn/Cl in CR was calculated as 0.272. Therefore, zinc contained in CR can react with only 54.4% of chlorine in CR, and the observed yield of chlorine contained in the WS constituent was consistent with the calculated yield of chlorine reacted with zinc. Accordingly, it was considered that 40% of chlorine in CR could not react with ZnO in CR and stabilized with the gaseous or volatile

WN WC + YC WN + WC WN + WC

(1)

where WN and WC are feed amounts (in grams) of NR and CR upon coliquefaction, respectively, and YN and YC are yields (%) of constituents from the individual liquefaction of NR and CR in Figure 2, respectively. From Figure 2, upon coliquefaction of NR and CR above 360 °C, the residue yield decreased by 5% and the oil yield increased by 5% in comparison to the calculated yield. From Figure 3, upon coliquefaction of NR and CR, the yield of volatile chlorine almost disappeared and over 83% of chlorine was contained in the WS constituent. The chlorine-containing organic volatiles detected after the liquefaction of CR alone did not appear after the coliquefaction of NR and CR at any liquefaction temperature (300-420 °C). It was apparent that the chlorine in CR reacted with not only zinc in CR but also zinc in NR to form ZnCl2 in the WS constituent. Upon coliquefaction of NR and CR, feed amounts of NR and CR were prepared so that the atomic ratio of Zn and Cl in the mixture of NR and CR would be 1:1. Therefore, the amount of zinc in the autoclave was estimated to be sufficient for the reaction with chlorine in CR. Accordingly, coliquefaction of CR with NR was clarified as the effective process for both the increase of the oil yield and the removal of chlorine as a WS constituent. Effects of the Mixing Ratio of NR on Coliquefaction. In an attempt to enhance the reaction of chlorine in CR with zinc in CR and NR, the effect of the mixing ratio of NR upon coliquefaction was evaluated. The effects of the mixing ratio of NR on the product yields and the chlorine distributions after coliquefaction of NR and CR at 360 °C are shown in Figures 4 and 5, respectively. The feed amounts of NR and CR were prepared so that the atomic ratio of Zn/Cl in the mixture of NR and CR will be any one of 1:1, 2:1, and 4:1. In Figure 4, upon liquefaction of CR with a relatively small proportion of NR (13) Sugano, M.; Onda, D.; Mashimo, K. Energy Fuels 2006, 20, 2713– 2716.

Dechlorination of CR by Coliquefaction with NR

Figure 5. Effects of the mixing ratio of NR on the chlorine distributions after the coliquefaction of NR and CR at 360 °C.

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Figure 8. Effects of the solvent on the product yields after the coliquefaction of NR and CR at 360 °C.

Figure 6. Additive effects of ZnO on the product yields after the liquefaction of CR at 360 °C. Figure 9. Effects of the solvent on the chlorine distributions after the coliquefaction of NR and CR at 360 °C.

Figure 7. Additive effects of ZnO on the chlorine distributions after the liquefaction of CR at 360 °C.

(Zn/Cl ) 1:1), the residue yield decreased and the oil yield increased in comparison to the calculated yield. However, these variations in yields decreased with the increase of the proportion of NR in the mixture (high Zn/Cl ratio). As shown in Figure 5, the yield of chlorine contained in the WS constituent decreased with the increase of the Zn/Cl ratio. Therefore, the increase of the proportion of NR did not affect the upgrading reaction of the mixture and the reaction of chlorine with zinc. With the increase of the Zn/Cl ratio, the amount of radicals from NR increased during the coliquefaction. Accordingly, it was considered that the probability of the stabilization of radicals from NR by HCl from CR was enhanced upon coliquefaction of a high Zn/Cl ratio, which resulted as the decreases of the oil yield and chlorine contained in the WS constituent. Additive Effects of Zinc Oxide on the Liquefaction of CR. To discuss the additive effect of the organic constituent of the NR on the liquefaction of CR, the liquefaction of CR with ZnO addition was carried out. The amount of ZnO was added so that the atomic ratio of Zn/Cl in the reactants in the autoclave will be 4:1. The product yields and the chlorine distributions after the liquefaction of CR with or without ZnO at 360 °C were shown in Figures 6 and 7, respectively. Those yields after the liquefaction of CR alone were given in Figures 6 and 7 for comparison. The chlorine distribution after the coliquefaction of CR and NR (Zn/Cl ) 4:1) was also shown in Figure 7 for comparison. From Figure 6, the addition of ZnO did not affect the upgrading reaction of CR. As shown in Figure 7, the yield of chlorine contained in the WS constituent decreased significantly upon the addition of ZnO. Further, in comparison to the coliquefaction of CR and NR (Zn/Cl ) 4:1), the decrease of chlorine contained in the WS constituent and the increase of

chlorine contained in the WI constituent were observed. Upon coliquefaction of CR and NR, it was expected that ZnO in NR did not disperse into the reactant below the melting temperature of NR. Therefore, it was considered that the reaction of chlorine in CR with zinc in both CR and NR was enhanced upon coliquefaction because the temperature of the formation of HCl from CR and the temperature of dispersion of ZnO from NR into the reactant were close. Moreover, upon coliquefaction of CR and NR, radicals from CR were anticipated to be stabilized with easily formed radicals from NR because the addition of ZnO alone did not affect the upgrading reaction of CR. Accordingly, the synergistic effects for upgrading the reaction, such as the increase of the oil yield and the decrease of the residue yield, were observed upon coliquefaction. Effects of the Kind of Solvent upon Coliquefaction. The product yields and the chlorine distributions after coliquefaction of CR and NR with either undecane or 1-methylnaphthalene (1-MN) as the solvent at 360 °C were shown in Figures 8 and 9, respectively. Those yields after the coliquefaction of CR and NR with decalin as the solvent were also shown in Figures 8 and 9 for comparison. In comparison to the coliquefaction with decalin, the increase of the residue yield and the decreases of the yields of oil and chlorine contained in the WS constituent were observed. From the observation of the swelling behavior of NR and CR in the solvent, both NR and CR swelled well in decalin compared to undecane and 1-MN. Therefore, upon coliquefaction of CR and NR with decalin, it was considered that the upgrading reaction of NR and CR, such as the decrease of the residue yield and the increase of the oil yield, and the reaction of chlorine in CR with zinc in CR and NR were enhanced by the mixing of molecules in NR and CR because both rubber samples swelled well in the decaline solvent. Effects of Vulcanization and Carbon-Black Addition upon Coliquefaction. In an attempt to operate the liquefaction of the real waste rubber, the effects of vulcanization and carbonblack addition upon coliquefaction of NR and CR were discussed. The product yields and the chlorine distributions after the coliquefaction of VNRC and VCRC (vulcanized CR and NR with carbon black) at 360 °C were shown in Figures 10 and 11, respectively. The product yields in Figure 10 were represented as moisture, ash,

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residue yield and the increase of the oil yield, appeared upon coliquefaction of VNRC and VCRC. Conclusions

Figure 10. Effects of vulcanization and carbon-black addition on the product yields after the coliquefaction of NR and CR at 360 °C.

Figure 11. Effects of vulcanization and carbon-black addition on the chlorine distributions after the coliquefaction of NR and CR at 360 °C.

and carbon-black free basis. The vulcanization and carbon-black addition did not affect the product yields and the chlorine distribution. As well as the coliquefaction of unvulcanized CR and NR (Figure 2), the synergistic effects of the upgrading reaction of both rubber samples, such as the decrease of the

(1) In comparison to the individual liquefaction of CR and NR, the synergistic effects of the upgrading reaction, such as the decrease of the residue yield and the increase of the oil yield, and the reaction of chlorine in CR with zinc in CR and NR were enhanced by the coliquefaction of CR and NR. (2) In comparison to the coliquefaction (Zn/Cl ) 2:1 or 4:1), the reaction of chlorine in CR with zinc in CR and NR was enhanced upon coliquefaction (Zn/Cl ) 1:1). (3) The synergistic effects of upgrading and the enhancement of the reaction of chlorine in CR with zinc in CR and NR, which were observed upon coliquefaction, did not occur on the liquefaction of CR with the addition ZnO powder only. (4) The synergistic effects of upgrading and the enhancement of the reaction of chlorine in CR with zinc in CR and NR upon coliquefaction were observed because both CR and NR swelled well in decalin. (5) The vulcanization with carbon-black addition did not affect the product yields and the chlorine distribution upon coliquefaction. However, the synergistic effects of the upgrading also appeared upon coliquefaction of vulcanized CR and NR containing carbon black. Acknowledgment. The authors are grateful to Ms. Mina Sanada and Mr. Katsuhiko Takai (Nihon University) for their support of this study. EF700733E