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Comparative study on conversion of C8 and C16 paraffins on ZSM-5 catalysts
Zeolites and Related Materials: Trends, Targets and Challenges Proceedings of 4th International FEZA Conference A. Gédéon, P. Massiani and F. Babonneau (Editors) © 2008 Elsevier B.V. All rights reserved.
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Comparative study on conversion of C8 and C16 paraffins on ZSM-5 catalysts D.G. Aksenov, O.V. Kikhtyanin, and G.V. Echevsky Boreskov Institute of Catalysis, SB RAN, Lavrentiev Ave., 5, Novosibirsk, 630090, Russia +7 383 3309827 ([email protected])
Abstract A comparative study of conversion of n-octane and n-hexadecane in conditions of BIMF process was performed to follow reaction pathways and to estimate advantages to use heavier distillates for obtaining high-quality fuels. It was found that the conversion of both n-octane and n-hexadecane depends on reaction pressure, and the yield of liquid reaction products is higher in the case of heavier feed. However products of n-octane conversion demonstrate more stable behavior with TOS (Time On Stream). Benzene content is lower in the case of n-hexadecane. A positive effect of heavier hydrocarbons in minimizing dealkylated aromatics content was demonstrated by special experiments. Keywords: MFI zeolite, n-alkanes, benzene
1. Introduction BIMF process (Boreskov Institute Motor Fuels) represents a new catalytic process for the one-stage conversion of gas condensates or oil distillates with b.p. up to 360°C to high-octane gasoline, diesel fuel (winter grade) and gases C3-C4 [1, 2]. The gasoline produced contains less than 35 wt.% of aromatics, up to 10 wt.% of n-alkanes, the rest being iso-alkanes and naphthenes. The main task is to convert n-alkanes which present both in gasoline and diesel parts of feedstock. This work deals with comparative study of conversion of n-octane and n-hexadecane in conditions of BIMF process to follow reaction pathways and to estimate advantages to use heavier distillates for obtaining high-quality fuels.
2. Experimental The commercially available IC-30-BIMF (MFI structure) catalyst was used in the present work. Catalytic tests were carried out on a flow installation equipped with a tubular SS reactor (10 cm3) with a fixed catalyst bed. Studies of conversion of n-octane and n-hexadecane without or with aromatics additives (5 wt.% of benzene) were performed at 350°C, 0-2.0 MPa and WHSV = 1.5-1.6 h-1. Reaction products were analyzed using an Agilent-6850 GC unit.
3. Results and Discussion It is found that conversion of both n-octane and n-hexadecane increases when reaction pressure grows up to 1.0-1.5 MPa; nevertheless, higher pressure causes slight decrease of the feed conversion. In both cases a substantial formation of light hydrocarbons is observed at the beginning of a catalytic run; however, when TOS increases, yield of liquid hydrocarbons simultaneously increases. In gaseous part hydrocarbons C3-C4 (mainly paraffinic) makes up to 96-98 wt.% with a very low content of C1-C2 products.
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It is found also that yield of liquid reaction products is higher in the case of heavier feed (Table 1). Table 1. Formation of gaseous and liquid hydrocarbons during conversion of n-octane and n-hexadecane. T = 350°C, P= 1.0 MPa, WHSV=1.6 h-1. TOS, n-octane n-hexadecane hours Conver Content of Content of Convers Content of Content of sion, % gas liquid ion, % gas liquid products, products, products, products, wt.% wt.% wt.% wt.% 3 95.6 60.2 39.8 96.5 45.3 54.7 5 98.7 57.2 42.8 98.1 43.1 56.9 7 99.6 55.6 44.4 99.1 38.1 61.9 9 99.7 53.7 46.3 99.7 31.2 68.8 Table 2. Group composition of liquid hydrocarbons produced from n-octane and nhexadecane. T = 350°C, P= 1.0 MPa, WHSV=1.6 h-1. TOS, n-octane n-hexadecane hours n-alka isonaph aroma n-alka isonaph aroma nes alka thenes tics nes alka thenes tics nes nes 3 30.6 34.5 1.8 33.1 28.5 32.9 1.6 36.9 5 24.2 35.8 2 38 26.5 33.9 1.8 37.8 7 23 36.8 2.2 38.1 27.3 31.5 2.1 36.9 9 23.9 35.5 2.4 38.2 30.4 32.4 2.3 34.9 Group composition of liquid products is presented in Table 2. It is seen that in the case of n-octane conversion the catalyst demonstrates more stable behavior with TOS. To calculate MON (Motor Octane Number) of gasoline fraction according to a method given in [3] GC composition data have been used. This value is higher for n-octane and amounts to 82-83 comparatively with 79-80 for n-hexadecane. In the aromatic part, benzene content slightly decreases with TOS but in all experiments its amount is higher in the case of n-octane (~0.4 wt.%) than in the case of n-hexadecane (~0.2-0.3 wt.%). Table 3. Formation of gaseous and liquid hydrocarbons during conversion of n-octane, n-hexadecane and their mixture. T = 350°C, P= 1.2 MPa, WHSV=1.5 h-1. TOS, n-octane n-hexadecane n-C8 + n-C16 (50:50) hours Content of Content of Content of Content of Content of Content gas liquid gas liquid gas of liquid products, products, products, products, products, products, wt.% wt.% wt.% wt.% wt.% wt.% 3 62.18 37.82 55.19 44.81 55.48 44.52 5 59.87 40.13 52.26 47.74 52.85 47.15 7 56.95 43.05 49.71 50.29 50.33 49.67 9 53.80 46.20 46.21 53.79 46.28 53.72 Yields of gaseous and liquid products at transformation of mixture of n-alkanes (50 wt.% of n-octane and 50 wt.% of n-hexadecane) are very close to those at conversion of
Comparative study on conversion of C8 and C16 paraffins on ZSM-5 catalysts
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n-hexadecane (Table 3). Data presented in Table 4 on composition of individual hydrocarbons show the same tendency: yields of n-alkanes and aromatics compound during transformation of pure n-hexadecane and mixture of n-octane and n-hexadecane are very close. Yields of naphthenes are similar in all experiments. Table 4. Yields of individual compounds during conversion of n-octane, n-hexadecane and their mixture. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1. compound n-octane n-hexadecane n-C8 + n-C16 (50:50) n-butane 17.06 14.97 14.54 n-hexane 1.72 2.09 2.00 n-heptane 0.42 0.54 0.52 toluene 2.09 2.81 2.68 ethylbenzene 0.81 1.20 1.07 xylenes 4.29 5.34 5.28 C6H3(CH3)3 0.95 1.24 1.22 propylbenzenes 0.18 0.26 0.25 methylcyclopentane 0.41 0.42 0.43 cyclohexane 0.05 0.04 0.05 metylcyclohexane 0.39 0.35 0.38 A positive effect of heavier hydrocarbons in minimizing dealkylated aromatics content has been demonstrated by special experiments with benzene addition (5 wt.%) to a paraffinic feed. Conversion of benzene is found to be 70% for n-hexadecane and 60% for n-octane. In both cases benzene transforms mainly to ethylbenzene, propylbenzenes and butylbenzenes. Distribution of products of benzene transformation is presented in Fig. 1. It is seen that content of butylbenzenes is equal for all feeds, but yield of propylbenzenes is higher for n-hexadecane and yield of ethylbenzene higher for noctane. It is found also that yield of aromatic compounds is higher in the case of nhexadecane especially towards heavier reaction compounds (Fig. 2).
n-octane
ethylbenzene butylbenzenes
propylbenzenes
n-hexadecane
ethylbenzene
propylbenzenes
butylbenzenes
Figure 1. Distribution of alkylated aromatics resulting from benzene transformation. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1.
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Figure 2. Yields of various aromatic compounds resulting from conversion of the mixture [n-paraffin (95%) + benzene (5%)]. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1. Thus, it is seen that conversion of n-paraffins in a broad range of fraction compositions on ZSM-5 catalyst possesses a number of advantages comparatively with transformation of hydrocarbons of gasoline fraction. Conversion of heavier feed results in an increasing yield of liquid reaction products; however, group composition of hydrocarbons doesn’t vary to a great extent. Total content of aromatics is approximately the same for all experiments, but heavier feed results in a formation of more alkylated aromatic products. It is more evident in experiments with additional benzene: its conversion as well as total yield of aromatic compounds is higher in the case of nhexadecane especially towards heavier reaction products. Obtained experimental data are discussed in the sight of possible technological schemes of transformation of different hydrocarbon feedstocks to produce high-quality motor fuels. References [1] O.V. Klimov, D.G. Aksenov, I.P. Prosvirin, A.V. Toktarev, M.N. Razheva and G.V. Echevsky, Stud. Surf. Sci. Catal., 158 (2005) 1779. [2] G.V. Echevsky, O.V. Kikhtyanin, D.G. Aksenov and O.V. Klimov, Scientific Base and Tehnology of BIMF (“Boreskov Institute Motor Fuels”) process. New challenges in catalysis IV. Editor Paula Putanov, Belgrade 2006, . 123. [3] S.V. Cherepitsa, S.M. Bychkov and S.V.Gaciha, Khimiya i Tekhnologiya Topliv i Masel (in Russian) 4 (2001) 44.
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Comparative study on conversion of C8 and C16 paraffins on ZSM-5 catalysts D.G. Aksenov, O.V. Kikhtyanin, and G.V. Echevsky Boreskov Institute of Catalysis, SB RAN, Lavrentiev Ave., 5, Novosibirsk, 630090, Russia +7 383 3309827 ([email protected])
Abstract A comparative study of conversion of n-octane and n-hexadecane in conditions of BIMF process was performed to follow reaction pathways and to estimate advantages to use heavier distillates for obtaining high-quality fuels. It was found that the conversion of both n-octane and n-hexadecane depends on reaction pressure, and the yield of liquid reaction products is higher in the case of heavier feed. However products of n-octane conversion demonstrate more stable behavior with TOS (Time On Stream). Benzene content is lower in the case of n-hexadecane. A positive effect of heavier hydrocarbons in minimizing dealkylated aromatics content was demonstrated by special experiments. Keywords: MFI zeolite, n-alkanes, benzene
1. Introduction BIMF process (Boreskov Institute Motor Fuels) represents a new catalytic process for the one-stage conversion of gas condensates or oil distillates with b.p. up to 360°C to high-octane gasoline, diesel fuel (winter grade) and gases C3-C4 [1, 2]. The gasoline produced contains less than 35 wt.% of aromatics, up to 10 wt.% of n-alkanes, the rest being iso-alkanes and naphthenes. The main task is to convert n-alkanes which present both in gasoline and diesel parts of feedstock. This work deals with comparative study of conversion of n-octane and n-hexadecane in conditions of BIMF process to follow reaction pathways and to estimate advantages to use heavier distillates for obtaining high-quality fuels.
2. Experimental The commercially available IC-30-BIMF (MFI structure) catalyst was used in the present work. Catalytic tests were carried out on a flow installation equipped with a tubular SS reactor (10 cm3) with a fixed catalyst bed. Studies of conversion of n-octane and n-hexadecane without or with aromatics additives (5 wt.% of benzene) were performed at 350°C, 0-2.0 MPa and WHSV = 1.5-1.6 h-1. Reaction products were analyzed using an Agilent-6850 GC unit.
3. Results and Discussion It is found that conversion of both n-octane and n-hexadecane increases when reaction pressure grows up to 1.0-1.5 MPa; nevertheless, higher pressure causes slight decrease of the feed conversion. In both cases a substantial formation of light hydrocarbons is observed at the beginning of a catalytic run; however, when TOS increases, yield of liquid hydrocarbons simultaneously increases. In gaseous part hydrocarbons C3-C4 (mainly paraffinic) makes up to 96-98 wt.% with a very low content of C1-C2 products.
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It is found also that yield of liquid reaction products is higher in the case of heavier feed (Table 1). Table 1. Formation of gaseous and liquid hydrocarbons during conversion of n-octane and n-hexadecane. T = 350°C, P= 1.0 MPa, WHSV=1.6 h-1. TOS, n-octane n-hexadecane hours Conver Content of Content of Convers Content of Content of sion, % gas liquid ion, % gas liquid products, products, products, products, wt.% wt.% wt.% wt.% 3 95.6 60.2 39.8 96.5 45.3 54.7 5 98.7 57.2 42.8 98.1 43.1 56.9 7 99.6 55.6 44.4 99.1 38.1 61.9 9 99.7 53.7 46.3 99.7 31.2 68.8 Table 2. Group composition of liquid hydrocarbons produced from n-octane and nhexadecane. T = 350°C, P= 1.0 MPa, WHSV=1.6 h-1. TOS, n-octane n-hexadecane hours n-alka isonaph aroma n-alka isonaph aroma nes alka thenes tics nes alka thenes tics nes nes 3 30.6 34.5 1.8 33.1 28.5 32.9 1.6 36.9 5 24.2 35.8 2 38 26.5 33.9 1.8 37.8 7 23 36.8 2.2 38.1 27.3 31.5 2.1 36.9 9 23.9 35.5 2.4 38.2 30.4 32.4 2.3 34.9 Group composition of liquid products is presented in Table 2. It is seen that in the case of n-octane conversion the catalyst demonstrates more stable behavior with TOS. To calculate MON (Motor Octane Number) of gasoline fraction according to a method given in [3] GC composition data have been used. This value is higher for n-octane and amounts to 82-83 comparatively with 79-80 for n-hexadecane. In the aromatic part, benzene content slightly decreases with TOS but in all experiments its amount is higher in the case of n-octane (~0.4 wt.%) than in the case of n-hexadecane (~0.2-0.3 wt.%). Table 3. Formation of gaseous and liquid hydrocarbons during conversion of n-octane, n-hexadecane and their mixture. T = 350°C, P= 1.2 MPa, WHSV=1.5 h-1. TOS, n-octane n-hexadecane n-C8 + n-C16 (50:50) hours Content of Content of Content of Content of Content of Content gas liquid gas liquid gas of liquid products, products, products, products, products, products, wt.% wt.% wt.% wt.% wt.% wt.% 3 62.18 37.82 55.19 44.81 55.48 44.52 5 59.87 40.13 52.26 47.74 52.85 47.15 7 56.95 43.05 49.71 50.29 50.33 49.67 9 53.80 46.20 46.21 53.79 46.28 53.72 Yields of gaseous and liquid products at transformation of mixture of n-alkanes (50 wt.% of n-octane and 50 wt.% of n-hexadecane) are very close to those at conversion of
Comparative study on conversion of C8 and C16 paraffins on ZSM-5 catalysts
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n-hexadecane (Table 3). Data presented in Table 4 on composition of individual hydrocarbons show the same tendency: yields of n-alkanes and aromatics compound during transformation of pure n-hexadecane and mixture of n-octane and n-hexadecane are very close. Yields of naphthenes are similar in all experiments. Table 4. Yields of individual compounds during conversion of n-octane, n-hexadecane and their mixture. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1. compound n-octane n-hexadecane n-C8 + n-C16 (50:50) n-butane 17.06 14.97 14.54 n-hexane 1.72 2.09 2.00 n-heptane 0.42 0.54 0.52 toluene 2.09 2.81 2.68 ethylbenzene 0.81 1.20 1.07 xylenes 4.29 5.34 5.28 C6H3(CH3)3 0.95 1.24 1.22 propylbenzenes 0.18 0.26 0.25 methylcyclopentane 0.41 0.42 0.43 cyclohexane 0.05 0.04 0.05 metylcyclohexane 0.39 0.35 0.38 A positive effect of heavier hydrocarbons in minimizing dealkylated aromatics content has been demonstrated by special experiments with benzene addition (5 wt.%) to a paraffinic feed. Conversion of benzene is found to be 70% for n-hexadecane and 60% for n-octane. In both cases benzene transforms mainly to ethylbenzene, propylbenzenes and butylbenzenes. Distribution of products of benzene transformation is presented in Fig. 1. It is seen that content of butylbenzenes is equal for all feeds, but yield of propylbenzenes is higher for n-hexadecane and yield of ethylbenzene higher for noctane. It is found also that yield of aromatic compounds is higher in the case of nhexadecane especially towards heavier reaction compounds (Fig. 2).
n-octane
ethylbenzene butylbenzenes
propylbenzenes
n-hexadecane
ethylbenzene
propylbenzenes
butylbenzenes
Figure 1. Distribution of alkylated aromatics resulting from benzene transformation. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1.
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Figure 2. Yields of various aromatic compounds resulting from conversion of the mixture [n-paraffin (95%) + benzene (5%)]. T = 350°C, P= 1.0 MPa, WHSV=1.5 h-1. Thus, it is seen that conversion of n-paraffins in a broad range of fraction compositions on ZSM-5 catalyst possesses a number of advantages comparatively with transformation of hydrocarbons of gasoline fraction. Conversion of heavier feed results in an increasing yield of liquid reaction products; however, group composition of hydrocarbons doesn’t vary to a great extent. Total content of aromatics is approximately the same for all experiments, but heavier feed results in a formation of more alkylated aromatic products. It is more evident in experiments with additional benzene: its conversion as well as total yield of aromatic compounds is higher in the case of nhexadecane especially towards heavier reaction products. Obtained experimental data are discussed in the sight of possible technological schemes of transformation of different hydrocarbon feedstocks to produce high-quality motor fuels. References [1] O.V. Klimov, D.G. Aksenov, I.P. Prosvirin, A.V. Toktarev, M.N. Razheva and G.V. Echevsky, Stud. Surf. Sci. Catal., 158 (2005) 1779. [2] G.V. Echevsky, O.V. Kikhtyanin, D.G. Aksenov and O.V. Klimov, Scientific Base and Tehnology of BIMF (“Boreskov Institute Motor Fuels”) process. New challenges in catalysis IV. Editor Paula Putanov, Belgrade 2006, . 123. [3] S.V. Cherepitsa, S.M. Bychkov and S.V.Gaciha, Khimiya i Tekhnologiya Topliv i Masel (in Russian) 4 (2001) 44.