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Transformation of C1C4 Alcohols into Hydrocarbons on an Amorphous Silica–Alumina Catalyst
Applied Catalysis, 36 (1988) 299-306 Elsevier Science Publishers B.V.. Amsterdam -
299
Printed in The Netherlands
Transformation of C1-C4 Alcohols into Hydrocarbons on an Amorphous Silica-Alumina Catalyst R.A. COMELLI and N.S. FIGOLI* Znstituto de Investigaciones en Catcilisisy Petroquimica INCAPE Santiago de1 Ester0 2654, 3000 Santa Fe (Argentina) (Received 8 May 1987, accepted 14 August 1987)
ABSTRACT The transformation of ethanol, 2-propanol and 2-butanol into hydrocarbons has been studied on an amorphous silica-alumina and the results compared with those obtained earlier for methanol. Experiments were carried out at temperatures ranging from 310 to 45O”C, contact times from 1 to 14 h, and atmospheric pressure. Ethanol produced only ethene, while the other alcohols produced hydrocarbons containing up to twelve carbon atoms. The highest liquid yield was obtained from methanol. According to the product distribution ethene did not appear as the precursor in the hydrocarbon chain growth.
INTRODUCTION
The transformation of methanol into hydrocarbons has been widely studied in recent years [l-3], since Mobil patented the zeolite ZSM-5 [ 41 and the MTG process [ 51 attracted worldwide attention. The first commercial plant, located in New Zealand, has been on stream since the fall of 1985. Acidity is one of the main properties of the catalyst making it capable of transforming methanol into hydrocarbons. Shape selectivity has been used to explain product distribution [ 6,7] and stability [ 81. Nevertheless, the maximum number of carbon atoms in the product, either on ZSM-5 or other catalysts of larger pore diameters, is around twelve carbon atoms. It was concluded [ 91 that the maximum product size obtained during the transformation of methanol into hydrocarbons was a consequence of operational conditions and other process characteristics. Some amorphous silica-aluminas have shown good activity and stability for the above-mentioned transformation [ 10 1. The search for alternative raw materials from which hydrocarbons to be used as fuels or in petrochemical plants can be obtained, extended the studies of the transformation of methanol to other alcohols and oxygenated compounds [II]. We have studied the transformation of ethanol, 2-propanol and 2-butanol into
0166-9834/88/$03.50
0 1988 Elsevier Science Publishers B.V.
300
hydrocarbons on an amorphous silica-alumina. Results using methanol as feed have been published previously [ 10,121. EXPERIMENTAL
Catalyst A commercial amorphous silica-alumina of 559 m2 g-l specific surface area, 0.633 cm3 g-l pore volume, 45 A mean pore diameter, and 11.34 siIica:alumina molar ratio was used. Silica-alumina acidity determined by ammonia therma programmed desorption following the procedure described in ref. 13 was 0.176, 0.111 and 0.063 meq ammonia (g cat) -’ for weak ( 250-350” C ) , medium (350-450” C ) , and strong (450-550 “C ) acidity, respectively. Reactants Pure ethanol and 2-propanol (Merck) and 2-butanol (Carlo Erba RPE) were used as feed, without further purification. Measurement of catalytic activity and selectivity Experiments were carried out at atmospheric pressure using a continuous flow fixed bed reactor. Reactants were fed into the reactor by means of a syringe pump and were vaporized before entering the reactor. Analysis of reaction products was made by on-line gas chromatography, as previously described
[121*
Coke deposited on the catalysts was determined by combustion-volumetry at the end of the activity tests. RESULTS AND DISCUSSION
Ethanol as feed Measurements of catalytic activity and selectivity were performed at temperatures from 310 to 420°C and contact times (weight of catalyst per mass flow-rate of liquid) from 2 to 14 h. The results are presented in Table 1. As can be seen, the main reaction was dehydration of ethanol to ethene with only small amounts of other hydrocarbons being produced. At shorter times on stream (10 min) , the liquid hydrocarbon production was higher; e.g. 5.8% C,, at 380°C and 14 h contact time. But this production decreased quickly until it reached the stable values presented in Table 1. C,_, refers to paraffins, olefins and aromatics, toluene being the main aromatic product. C,, includes
301 TABLE 1 Product distribution at total conversion (Xr= 100%) in the reaction of ethanol on an amorphous silica-alumina under several operational conditions. Time on stream: 100 min T’(C) W/F(h)*
310 4
Hydrocarbon product distribution ( % ) C, C, C, C, G-7 C 8+
340 4
0 99.5 0.1 0.3 0.1 0
0 99.2 0.1 0.4 0.1 0.2
360 4
0 99.2 0.2 0.4 0 0.2
380 2
380 4
0 98.8 0.4 0.5 0.3 0
0.1 98.1 0.6 0.9 0.3 0
380 6
0.2 96.5 1.0 1.5 0.4 0.4
380 14
0.2 95.3 1.1 2.5 0.9 0
420 4
0.1 98.4 0.7 0.6 0.1 0.1
*Contact time (weight of catalyst per mass flow-rate of liquid).
alkyl substituted aromatics with a maximum of twelve carbon atoms. The hydrocarbon product distribution is quite different from that obtained when methanol was used as the feed [ 121. The amount of coke deposited on the catalyst after 450 min on stream increased with the reaction temperature (as shown in Fig. 1) but was not affected by the contact time. This behavior is qualitatively similar to the observed when the feed was methanol [lo]. Results obtained by several authors in the transformation of ethanol into hydrocarbons over ZSM-5 and other acidic catalysts are contradictory. Derouane et al. [ 141, working with ZSM-5 in a similar temperature range to that of our experiments, observed the formation of important amounts of hydrocarbons of higher molecular weight than ethene, when either methanol or ethanol were used as the feed. Nayak and Choudhary [ 151 found 25 and 28% aromatic hydrocarbons respectively, when feeding methanol or ethanol to ZSM5. Anunziata et al. [ 161 obtained 70-80% aromatics in the hydrocarbon prod-
300
380
420
TEMPERATURE
(“Cl
340
L
Fig. 1. Coke deposited on silica-alumina as a function of temperature. Feed: ( + ) ethanol; (0 ) 2propanol; (A ) 2-butanol. W/F=4 h; time on stream: 450 min.
302 TABLE 2 Product distribution at total conversion (X, = 100% ) in the reactions of 2-propanol on an amorphous silica-alumina under several operational conditions. Time on stream: 400 min T (“Cl
WfF (h)
340
360
4
4
1
2 12 8 15 3
Hydrocarbon product distribution ( % )
C2 c:,* C, C, i C,, (aromat.)
78 5 15 1
380 4
1 68 13 16 2
400 1
1 77 6 15 1
400 2.5
1 67 11 20 1
400 4
1 66 12 19 2
400 5.5
0 60 15 22 3
400 ‘7
1 60 15 21 3
420 4
1 67 13 17 2
450 4
1 68 14 15 2
*Around 100% propene.
uct distribution feeding either methanol or ethanol to ZSM-5. Chen and Garwood [ 171 obtained considerable amounts of C,+ and aromatic hydrocarbons with ethanol as feed, and the hydrocarbon product distribution was not very different from the one obtained when feeding methanol. A similar product distribution t.oours was obtained by Chen [ 181 when feeding diluted ethanol (8.7 vol.% ethanol), but our results were obtained using ethanol with no more than 0.2 wt.% of water. Anderson et al. [ 191 and Rajadhyaksha and Anderson [ 201 found that the passage of ethanol over ZSM-5 usually led to the generation of ethene without any higher hydrocarbon products, this being the usual behavior at low reactivity. Espinoza et al. [ 211 found that the principal product of the reaction of ethanol on an amorphous silica-alumina was ethene, although they obtained the same product distribution as that obtained with ZSM-5 when methanol was used as the feed. It, can be concluded that more similarities in the hydrocarbon production and hydrocarbon product distribution were observed by the different authors that have worked in the field when methanol was fed either to ZSM-5 or to silica-aluminas than when ethanol was used as the feed. Catalyst properties seem to be important factors in the transformation of ethanol into hydrocarbons. According to our results, ethene was almost the only product when the feed was ethanol, and coke deposition was important although there were no aromatic hydrocarbons (considered important coke precursors, refs. 22 and 23) in the reaction product, as there were when methanol was used as the feed. [ lo], 2-Propanol
as feed
Experiments were carried out from 340 to 450°C changing c,ontact time from to 7 h with the results presented in Table 2. For the wide range of temperatures and contact times studied, there were no important modifications in the 1
303
o
+-+-++-I
0
400
200 TIME
(min)
Fig. 2. Conversion into liquid hydrocarbons, Xc:s+ (water excluded), as a function of the time on stream for different alcohols as feed ( l ) methanol (from ref. 12) ; ( + ) ethanol;(0 1 P-propanol; (A) 2-butanol. T=38O”C, W/F=4 h.
total conversion or in the hydrocarbon product distribution. Propene and hydrocarbons with five to seven carbon atoms where the most important products in the gaseous and liquid fraction respectively. Aromatics with eight or more carbon atoms, which were an important fraction when the feed was methanol, were produced in very small amounts. A decrease in the amount of liquid and an increase in gaseous hydrocarbons (see Fig. 2) with the time on stream were observed. Ether was not produced under any of the conditions studied. Although the hydrocarbon product distribution did not change considerably when the temperature was increased, such an increase produced larger amounts of coke on the catalysts, as shown in Fig. 1. Coke deposition was not affected by the contact time. Even though different oxygenated compounds have been used as feed in order to obtain hydrocarbons in the gasoline range [ 241, there are only a few references to the use of 2-propanol for the same objective. Our results showed that propene was the hydrocarbon produced in largest amounts, The most important liquid hydrocarbon fraction was observed in the C&-C, range, and coke deposition was more important, in the range of temperature and contact time studied, than when the feed was methanol and the reaction product included aromatic hydrocarbons. 2-Butanol
as feed
Experiments were carried out at temperatures from 340 to 420 ‘C and contact times from 1 to 5.5 h, conditions under which total 2-butanol conversion was observed. The results are presented in Table 3. The most important liquid fraction was observed in the C,--C, range, hydrocarbons of four carbon atoms being the most important in the gaseous fraction. The largest amount of liquid hydrocarbons was obtained at 360’ C, and the production of such hydrocarbons increased with the contact time. The increment of temperature did not increase significantly the amount of
304 TABLE 3 Product distribution at total conversion (Xr= 100%) in the reaction of 2-butanol on an amorphous silica-alumina under several operational conditions. Time on stream: 400 min
T (“‘2) W/F(h) Hydrocarbon product distribution ( % ) C, C, C, C,., C,, (aromat.)
340 4
360 4
380 4
400 1
400 2.5
400 4
400 5.5
420 4
0 4 78 16 2
0 7 69 21 3
0 7 74 17 2
0 7 77 15 1
0 10 69 19 2
0 12 68 17 3
0 13 61 22 4
0 9 74 15 2
coke deposited on the catalysts, as shown in Fig. 1. Coke deposition was not affected by the contact time. As in the case of 2-propanol, there are very few references to the use of 2 butanol as the raw material from which to obtain hydrocarbons in the gasoline range on acidic catalysts. According to our results the C, fraction was the one produced in largest amounts, and the C,-C, fraction the most important among the liquid hydrocarbons produced. Considering the product distribution, there was no evidence of C, dimerization, very small amounts of Cs hydrocarbons being obtained. CONCLUSIONS
Comparing the behavior of methanol, ethanol, 2-propanol and 2-butanol during their transformation into hydrocarbons, we found that ethanol produced only ethene in important amounts, while the other alcohols produced considerable concentrations of other hydrocarbons. There exists a typical product distribution for each alcohol under the operational conditions studied. Data about methanol have been published elsewhere [ 121 while data about the three other alcohols are given in this paper. As mentioned above, ethene was practically the only product we obtained from ethanol (Table 1); this result allowed us to make some considerations about the role of precursor ascribed to ethene in the transformation of alcohols into hydrocarbons. Ethene has been considered by some authors [ 14,25,26] as the chain growth precursor in the transformation of methanol into hydrocarbons, meanwhile other authors attributed more importance to propene in the chain growth [ 19,21,27,28]. Itoh et al. [ 231 stated that ethene, once formed, can hardly react to form other hydrocarbons; Sayed and Cooney [ 291 stated that ethene seems unlikely to be involved in C-C bond formation. Because of these controversies, the intermediate generating the wide hydrocarbon spec-
305 TABLE 4 Coke deposited on the catalyst after 450 min on stream. Temperature = 380°C; W/F= 4 h Feed
Carbon ( % )
Methanol Ethanol 2-Propanol 2-Butanol
3.6* 2.8 6.2 6.7
*Data from ref. 12. T=370”C;
W/F=4.7
h.
trum is sometimes called “precursor” [ 12,301 when reaction schemes for the transformation of methanol into hydrocarbons are considered. According to our results during ethanol transformation on an amorphous silica-alumina, ethene is not capable of acting as precursor for larger hydrocarbons, as stated by several authors. During methanol conversion, the liquid hydrocarbons are mostly methyl or ethyl substituted benzenes [ 121, whereas from Z-propanol and 2-butanol the main liquid products are hydrocarbons with five to seven carbon atoms. As proposed by Itoh et al, [ 231, this difference in the liquid hydrocarbon distribution may be best understood in the following way. In the transformation of ethanol into hydrocarbons there must be a significant amount of C, and C2 adsorbed species, and reaction should proceed via these species. The C, and C, adsorbed species may act as reagents for the further alkylation of aromatics, and a wide distribution of methyl or ethyl substituted aromatics are produced. In the reaction of 2-propanol and 2-butanol, it seems that there are not too many C1 and Cz adsorbed species because methyl or ethyl substituted aromatics are not produced and the yield of C, and C, is small. This results in a characteristic product distribution for Z-propanol and 2-butanol, hydrocarbons with five to seven carbon atoms the main products. Only small amounts of aromatics with eight or more carbon atoms are observed. Since the Cs fraction is not important from 2-butanol, the chain growth is not produced by direct dimerization. C3 and C, fractions are the most important products from 2-propanol and 2butanol respectively; then, a rapid interconversion between C3 and Cd, as proposed when converting propene and l-butene over ZSM-5 [ 23,291, cannot be considered. Methanol is the raw material producing the largest liquid yield, followed by 2-propanol and 2-butanol; practically no liquid hydrocarbons are produced from ethanol, as shown in Fig. 2. Stability in liquid hydrocarbon production is almost the same for methanol, 2-propanol and 2-butanol, but the coke deposition is different, (see Table 4). In the conversion of ethanol, coke deposition is important, ethene being almost the only product. When the feed is methanol
306
the amount of coke deposited is larger andpolyalkyl-substituted aromatics can be considered important coke precursors, as stated by other authors [ 22,231. When the feed is 2-propanol or 2-butanol the amounts of coke deposited are the largest and the precursors may be either olefins (C, or C, respectively) or hydrocarbons with five to seven carbon atoms. 2-Propanol and 2-butanol as well as methanol seem to be important raw materials for hydrocarbon production on acidic catalysts, each alcohol having a characteristic product distribution.
REFERENCES
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
C.D. Change, Catal. Rev. Sci. Eng., 25 (1) (1983) 1. B.E. Langner, Appl. Catal., 2 (1982) 289. H. Hayashi and J.B. Moffat, J. Catal., 77 (1982) 473. R.J. Argauer and G.R. Landolt, U.S. Pat, 3 702 886 (1972) CD. Chang, A.J. Silvestri and R.L. Smith, U.S. Pat. 3 928 483 (1975). S.M. Csicsery, Pure & Appl. Chem., 58 (6) (1986) 841. P. Dejaifve, J. VQdrine, V. Bolis and E. Derouane, J. Catal., 63 (1980) 331. P. Dejaifve, A. Auroux, P. Gravelle, J. VBdrine, Z. Gabelica and E. Derouane, J. Catal., 70 (1981) 123. U.A. Sedran and N.S. Figoli, React. Kinet. Catal. Lett. (in press). U.A. Sedran, R.A. Comelli and N.S. Figoli, Appl. Catal., 11 (1984) 227. C. Chang and A. Silvestri, J. Catal., 47 (1977) 249. R.A. Comelli and N.S. Figoli, Appl. Catal., 30 (1987) 325. U.A. Sedran and N.S. Figoli, Appl. Catal., 19 (1985) 317. E. Derouane, J.B. Nagy, P. Dejaifve, J.H.C. Van Hooff, B.P. Spekman, J.C. VBdrine and C. Naccache, J. Catal., 53 (1978) 40. V.S. Nayak and V.R. Choudhary, Appl. Catal., 9 (1984) 251. O.A. Anunziata, O.A. Orio, E.R. Herrero, A.F. L6pez, CF. Pe’rez and A.R. Suairez, Appl. Catal., 15 (1985) 235. N.Y. Chen and W.E. Garwood, Catal. Rev. Sci. Eng., 28 (2-3) (1986) 185. N.Y. Chen, Chemtech, 13 (1983) 488. J.R. Anderson, K. Foger, T. Mole, R.A. Rajadhyaksha and J.V. Sanders, J. Catal., 58 (1979) 114. R.A. Rajadhyaksha and J.R. Anderson, J. Catal., 63 (1980) 510. R.L. Espinoza, CM. Stander and W.G.B. Mandersloot, Appl. Catal., 6 (1983) 11. D. Walsh and L. Rollman, J. Catal., 56 (1979) 195. H. Itoh, T. Hattori and Y. Murakami, Appl. Catal., 2 (1982) 19. C.D. Chang, N.Y.Chen, L.R. Koening and D.E. Walsh, Am. Chem. Sot., Div. Fuel Chem. Prepr., 28 (2) (1983) 146. W. Haag, R. Lago and P. Rodewald, J. Mol. Catal., 17 (1982) 161. D. Kagi, J. Catal., 69 (1981) 242. S. Ceckiewicz, J. Chem. Sot. Faraday Trans. 1,77 (1981) 269. R. Dessau and R. La Pierre, J. Catal., 78 (1982) 136. M.B. Sayed and R.P. Cooney, Aust. J. Chem., 35 (1982) 2483. R.A. Comelli, M.R. Sad and N.S. Figoli, React. Kinet. Catal. Lett., 33 (1987) 105.
299
Printed in The Netherlands
Transformation of C1-C4 Alcohols into Hydrocarbons on an Amorphous Silica-Alumina Catalyst R.A. COMELLI and N.S. FIGOLI* Znstituto de Investigaciones en Catcilisisy Petroquimica INCAPE Santiago de1 Ester0 2654, 3000 Santa Fe (Argentina) (Received 8 May 1987, accepted 14 August 1987)
ABSTRACT The transformation of ethanol, 2-propanol and 2-butanol into hydrocarbons has been studied on an amorphous silica-alumina and the results compared with those obtained earlier for methanol. Experiments were carried out at temperatures ranging from 310 to 45O”C, contact times from 1 to 14 h, and atmospheric pressure. Ethanol produced only ethene, while the other alcohols produced hydrocarbons containing up to twelve carbon atoms. The highest liquid yield was obtained from methanol. According to the product distribution ethene did not appear as the precursor in the hydrocarbon chain growth.
INTRODUCTION
The transformation of methanol into hydrocarbons has been widely studied in recent years [l-3], since Mobil patented the zeolite ZSM-5 [ 41 and the MTG process [ 51 attracted worldwide attention. The first commercial plant, located in New Zealand, has been on stream since the fall of 1985. Acidity is one of the main properties of the catalyst making it capable of transforming methanol into hydrocarbons. Shape selectivity has been used to explain product distribution [ 6,7] and stability [ 81. Nevertheless, the maximum number of carbon atoms in the product, either on ZSM-5 or other catalysts of larger pore diameters, is around twelve carbon atoms. It was concluded [ 91 that the maximum product size obtained during the transformation of methanol into hydrocarbons was a consequence of operational conditions and other process characteristics. Some amorphous silica-aluminas have shown good activity and stability for the above-mentioned transformation [ 10 1. The search for alternative raw materials from which hydrocarbons to be used as fuels or in petrochemical plants can be obtained, extended the studies of the transformation of methanol to other alcohols and oxygenated compounds [II]. We have studied the transformation of ethanol, 2-propanol and 2-butanol into
0166-9834/88/$03.50
0 1988 Elsevier Science Publishers B.V.
300
hydrocarbons on an amorphous silica-alumina. Results using methanol as feed have been published previously [ 10,121. EXPERIMENTAL
Catalyst A commercial amorphous silica-alumina of 559 m2 g-l specific surface area, 0.633 cm3 g-l pore volume, 45 A mean pore diameter, and 11.34 siIica:alumina molar ratio was used. Silica-alumina acidity determined by ammonia therma programmed desorption following the procedure described in ref. 13 was 0.176, 0.111 and 0.063 meq ammonia (g cat) -’ for weak ( 250-350” C ) , medium (350-450” C ) , and strong (450-550 “C ) acidity, respectively. Reactants Pure ethanol and 2-propanol (Merck) and 2-butanol (Carlo Erba RPE) were used as feed, without further purification. Measurement of catalytic activity and selectivity Experiments were carried out at atmospheric pressure using a continuous flow fixed bed reactor. Reactants were fed into the reactor by means of a syringe pump and were vaporized before entering the reactor. Analysis of reaction products was made by on-line gas chromatography, as previously described
[121*
Coke deposited on the catalysts was determined by combustion-volumetry at the end of the activity tests. RESULTS AND DISCUSSION
Ethanol as feed Measurements of catalytic activity and selectivity were performed at temperatures from 310 to 420°C and contact times (weight of catalyst per mass flow-rate of liquid) from 2 to 14 h. The results are presented in Table 1. As can be seen, the main reaction was dehydration of ethanol to ethene with only small amounts of other hydrocarbons being produced. At shorter times on stream (10 min) , the liquid hydrocarbon production was higher; e.g. 5.8% C,, at 380°C and 14 h contact time. But this production decreased quickly until it reached the stable values presented in Table 1. C,_, refers to paraffins, olefins and aromatics, toluene being the main aromatic product. C,, includes
301 TABLE 1 Product distribution at total conversion (Xr= 100%) in the reaction of ethanol on an amorphous silica-alumina under several operational conditions. Time on stream: 100 min T’(C) W/F(h)*
310 4
Hydrocarbon product distribution ( % ) C, C, C, C, G-7 C 8+
340 4
0 99.5 0.1 0.3 0.1 0
0 99.2 0.1 0.4 0.1 0.2
360 4
0 99.2 0.2 0.4 0 0.2
380 2
380 4
0 98.8 0.4 0.5 0.3 0
0.1 98.1 0.6 0.9 0.3 0
380 6
0.2 96.5 1.0 1.5 0.4 0.4
380 14
0.2 95.3 1.1 2.5 0.9 0
420 4
0.1 98.4 0.7 0.6 0.1 0.1
*Contact time (weight of catalyst per mass flow-rate of liquid).
alkyl substituted aromatics with a maximum of twelve carbon atoms. The hydrocarbon product distribution is quite different from that obtained when methanol was used as the feed [ 121. The amount of coke deposited on the catalyst after 450 min on stream increased with the reaction temperature (as shown in Fig. 1) but was not affected by the contact time. This behavior is qualitatively similar to the observed when the feed was methanol [lo]. Results obtained by several authors in the transformation of ethanol into hydrocarbons over ZSM-5 and other acidic catalysts are contradictory. Derouane et al. [ 141, working with ZSM-5 in a similar temperature range to that of our experiments, observed the formation of important amounts of hydrocarbons of higher molecular weight than ethene, when either methanol or ethanol were used as the feed. Nayak and Choudhary [ 151 found 25 and 28% aromatic hydrocarbons respectively, when feeding methanol or ethanol to ZSM5. Anunziata et al. [ 161 obtained 70-80% aromatics in the hydrocarbon prod-
300
380
420
TEMPERATURE
(“Cl
340
L
Fig. 1. Coke deposited on silica-alumina as a function of temperature. Feed: ( + ) ethanol; (0 ) 2propanol; (A ) 2-butanol. W/F=4 h; time on stream: 450 min.
302 TABLE 2 Product distribution at total conversion (X, = 100% ) in the reactions of 2-propanol on an amorphous silica-alumina under several operational conditions. Time on stream: 400 min T (“Cl
WfF (h)
340
360
4
4
1
2 12 8 15 3
Hydrocarbon product distribution ( % )
C2 c:,* C, C, i C,, (aromat.)
78 5 15 1
380 4
1 68 13 16 2
400 1
1 77 6 15 1
400 2.5
1 67 11 20 1
400 4
1 66 12 19 2
400 5.5
0 60 15 22 3
400 ‘7
1 60 15 21 3
420 4
1 67 13 17 2
450 4
1 68 14 15 2
*Around 100% propene.
uct distribution feeding either methanol or ethanol to ZSM-5. Chen and Garwood [ 171 obtained considerable amounts of C,+ and aromatic hydrocarbons with ethanol as feed, and the hydrocarbon product distribution was not very different from the one obtained when feeding methanol. A similar product distribution t.oours was obtained by Chen [ 181 when feeding diluted ethanol (8.7 vol.% ethanol), but our results were obtained using ethanol with no more than 0.2 wt.% of water. Anderson et al. [ 191 and Rajadhyaksha and Anderson [ 201 found that the passage of ethanol over ZSM-5 usually led to the generation of ethene without any higher hydrocarbon products, this being the usual behavior at low reactivity. Espinoza et al. [ 211 found that the principal product of the reaction of ethanol on an amorphous silica-alumina was ethene, although they obtained the same product distribution as that obtained with ZSM-5 when methanol was used as the feed. It, can be concluded that more similarities in the hydrocarbon production and hydrocarbon product distribution were observed by the different authors that have worked in the field when methanol was fed either to ZSM-5 or to silica-aluminas than when ethanol was used as the feed. Catalyst properties seem to be important factors in the transformation of ethanol into hydrocarbons. According to our results, ethene was almost the only product when the feed was ethanol, and coke deposition was important although there were no aromatic hydrocarbons (considered important coke precursors, refs. 22 and 23) in the reaction product, as there were when methanol was used as the feed. [ lo], 2-Propanol
as feed
Experiments were carried out from 340 to 450°C changing c,ontact time from to 7 h with the results presented in Table 2. For the wide range of temperatures and contact times studied, there were no important modifications in the 1
303
o
+-+-++-I
0
400
200 TIME
(min)
Fig. 2. Conversion into liquid hydrocarbons, Xc:s+ (water excluded), as a function of the time on stream for different alcohols as feed ( l ) methanol (from ref. 12) ; ( + ) ethanol;(0 1 P-propanol; (A) 2-butanol. T=38O”C, W/F=4 h.
total conversion or in the hydrocarbon product distribution. Propene and hydrocarbons with five to seven carbon atoms where the most important products in the gaseous and liquid fraction respectively. Aromatics with eight or more carbon atoms, which were an important fraction when the feed was methanol, were produced in very small amounts. A decrease in the amount of liquid and an increase in gaseous hydrocarbons (see Fig. 2) with the time on stream were observed. Ether was not produced under any of the conditions studied. Although the hydrocarbon product distribution did not change considerably when the temperature was increased, such an increase produced larger amounts of coke on the catalysts, as shown in Fig. 1. Coke deposition was not affected by the contact time. Even though different oxygenated compounds have been used as feed in order to obtain hydrocarbons in the gasoline range [ 241, there are only a few references to the use of 2-propanol for the same objective. Our results showed that propene was the hydrocarbon produced in largest amounts, The most important liquid hydrocarbon fraction was observed in the C&-C, range, and coke deposition was more important, in the range of temperature and contact time studied, than when the feed was methanol and the reaction product included aromatic hydrocarbons. 2-Butanol
as feed
Experiments were carried out at temperatures from 340 to 420 ‘C and contact times from 1 to 5.5 h, conditions under which total 2-butanol conversion was observed. The results are presented in Table 3. The most important liquid fraction was observed in the C,--C, range, hydrocarbons of four carbon atoms being the most important in the gaseous fraction. The largest amount of liquid hydrocarbons was obtained at 360’ C, and the production of such hydrocarbons increased with the contact time. The increment of temperature did not increase significantly the amount of
304 TABLE 3 Product distribution at total conversion (Xr= 100%) in the reaction of 2-butanol on an amorphous silica-alumina under several operational conditions. Time on stream: 400 min
T (“‘2) W/F(h) Hydrocarbon product distribution ( % ) C, C, C, C,., C,, (aromat.)
340 4
360 4
380 4
400 1
400 2.5
400 4
400 5.5
420 4
0 4 78 16 2
0 7 69 21 3
0 7 74 17 2
0 7 77 15 1
0 10 69 19 2
0 12 68 17 3
0 13 61 22 4
0 9 74 15 2
coke deposited on the catalysts, as shown in Fig. 1. Coke deposition was not affected by the contact time. As in the case of 2-propanol, there are very few references to the use of 2 butanol as the raw material from which to obtain hydrocarbons in the gasoline range on acidic catalysts. According to our results the C, fraction was the one produced in largest amounts, and the C,-C, fraction the most important among the liquid hydrocarbons produced. Considering the product distribution, there was no evidence of C, dimerization, very small amounts of Cs hydrocarbons being obtained. CONCLUSIONS
Comparing the behavior of methanol, ethanol, 2-propanol and 2-butanol during their transformation into hydrocarbons, we found that ethanol produced only ethene in important amounts, while the other alcohols produced considerable concentrations of other hydrocarbons. There exists a typical product distribution for each alcohol under the operational conditions studied. Data about methanol have been published elsewhere [ 121 while data about the three other alcohols are given in this paper. As mentioned above, ethene was practically the only product we obtained from ethanol (Table 1); this result allowed us to make some considerations about the role of precursor ascribed to ethene in the transformation of alcohols into hydrocarbons. Ethene has been considered by some authors [ 14,25,26] as the chain growth precursor in the transformation of methanol into hydrocarbons, meanwhile other authors attributed more importance to propene in the chain growth [ 19,21,27,28]. Itoh et al. [ 231 stated that ethene, once formed, can hardly react to form other hydrocarbons; Sayed and Cooney [ 291 stated that ethene seems unlikely to be involved in C-C bond formation. Because of these controversies, the intermediate generating the wide hydrocarbon spec-
305 TABLE 4 Coke deposited on the catalyst after 450 min on stream. Temperature = 380°C; W/F= 4 h Feed
Carbon ( % )
Methanol Ethanol 2-Propanol 2-Butanol
3.6* 2.8 6.2 6.7
*Data from ref. 12. T=370”C;
W/F=4.7
h.
trum is sometimes called “precursor” [ 12,301 when reaction schemes for the transformation of methanol into hydrocarbons are considered. According to our results during ethanol transformation on an amorphous silica-alumina, ethene is not capable of acting as precursor for larger hydrocarbons, as stated by several authors. During methanol conversion, the liquid hydrocarbons are mostly methyl or ethyl substituted benzenes [ 121, whereas from Z-propanol and 2-butanol the main liquid products are hydrocarbons with five to seven carbon atoms. As proposed by Itoh et al, [ 231, this difference in the liquid hydrocarbon distribution may be best understood in the following way. In the transformation of ethanol into hydrocarbons there must be a significant amount of C, and C2 adsorbed species, and reaction should proceed via these species. The C, and C, adsorbed species may act as reagents for the further alkylation of aromatics, and a wide distribution of methyl or ethyl substituted aromatics are produced. In the reaction of 2-propanol and 2-butanol, it seems that there are not too many C1 and Cz adsorbed species because methyl or ethyl substituted aromatics are not produced and the yield of C, and C, is small. This results in a characteristic product distribution for Z-propanol and 2-butanol, hydrocarbons with five to seven carbon atoms the main products. Only small amounts of aromatics with eight or more carbon atoms are observed. Since the Cs fraction is not important from 2-butanol, the chain growth is not produced by direct dimerization. C3 and C, fractions are the most important products from 2-propanol and 2butanol respectively; then, a rapid interconversion between C3 and Cd, as proposed when converting propene and l-butene over ZSM-5 [ 23,291, cannot be considered. Methanol is the raw material producing the largest liquid yield, followed by 2-propanol and 2-butanol; practically no liquid hydrocarbons are produced from ethanol, as shown in Fig. 2. Stability in liquid hydrocarbon production is almost the same for methanol, 2-propanol and 2-butanol, but the coke deposition is different, (see Table 4). In the conversion of ethanol, coke deposition is important, ethene being almost the only product. When the feed is methanol
306
the amount of coke deposited is larger andpolyalkyl-substituted aromatics can be considered important coke precursors, as stated by other authors [ 22,231. When the feed is 2-propanol or 2-butanol the amounts of coke deposited are the largest and the precursors may be either olefins (C, or C, respectively) or hydrocarbons with five to seven carbon atoms. 2-Propanol and 2-butanol as well as methanol seem to be important raw materials for hydrocarbon production on acidic catalysts, each alcohol having a characteristic product distribution.
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