ISBN 978-979-18962--7 Change in catalytic activity on acetone conversion to aromatic chemicals using H-ZSM-5 Setiadi 1, Slamet 1, Mohammad Nasikin 1, T. Tsutsui 2, T. Kojima 3 1 Jurusan Teknik Kimia, Fakultas Teknik Universitas Indonesia, Kampus UI, Depok-16424 e-mail: setiadi@che.ui.edu 2 Department of Applied Chemistry and Chemical Engineering, Kagoshima University, Kagoshima, Japan 3 Department of Applied Chemistry, Faculty of Engineering, Seikei University, Tokyo, Japan, e-mail: kojima@st.seikei.ac.jp Abstract This research is devoted to a catalytic process using H-ZSM-5 catalyst for the reaction of acetone conversion into aromatics chemicals. The reaction was performed in the continuous flow reactor under atmospheric pressure at temperature ranging 573-723 K. This work is intended to examine the change of H-ZSM-5 catalyst in reaction of acetone conversion on the various temperatures and effect of Si/Al atomic ratio. H-ZSM-5 with Si/Al = 25 was more active and stable than the Si/Al ratio 75 or 1, it indicates that the reaction of acetone conversion requires a high acid density of H-ZSM-5 catalyst. The yield of aromatic was obtained higher than 6 wt % during 6 h of reaction. The reaction on 673 K was the most favorable temperature for acetone conversion toward aromatic products. The high selectivity of mono-aromatic product indicates the H-ZSM-5 is shape selective catalyst for the formation of aromatic product and able to suppress the formation the poly-aromatic compound due to the geometrical size of pore. There is no negative effect due to the water addition on acetone conversion and aromatic product selectivities referring to the without the presence of water in the feed, it will simplify the industrial process. It is strongly predicted that the main causes of deactivation process is particularly due to the formation of coke, which was covered or blocked on the surface of H-ZSM-5 catalyst. Keywords:, Catalytic conversion, Si/Al ratio, ZSM-5 Introduction One of the promising route which is expected to be alternative process for producing aromatic compounds coming from a fermentation process which produce acetone, n-butanol or ethanol (Gibbs, 1983, Haggstrom, 1985). If the new route scheme for the production of aromatic compound as fuel or chemicals can be established perfectly, the biomassbased technology will have a greatly contributions to the solving of the energy problem significantly in the future. can be transformed into aromatics hydrocarbons through a catalytic process over HZSM- 5 (Chang & Silvestri, 1977; Lucas, 21, Lucas 1997, Setiadi, 23), but a sufficient study for the acetone aromatization especially on the stability of catalyst during reaction proceed is still lacking. The impressive result of the effect of temperature on the acetone conversion using ZSM-5 has been demonstrated by Chang et al. (1981), Chang and Silvestri (1977). But, the knowledge about the activity and stability on each temperature and the typical ratio of Si/Al of HZSM-5 catalyst were nothing. The acetone conversion into aromatic hydrocarbons products over HZSM-5 could be described by aldol condensation mechanism (Chang et al., 1981). This reaction mechanism combines both Bronsted-type (proton transfer) acid - base steps and Lewis base (electron transfer) steps. The aldol reaction of acetone begins with the abstraction of the acidic α-proton (Bronsted-Lowry step) to form a resonance-stabilized enolate anion (Xu, et. al., 22). This reactive anion acting as nucleophilic species attacks the electron poor carbonyl of an free acetone molecule (Lewis step) forming alkoxide intermediate (Xu et al., 1994), which is subsequently protonated to form the aldol molecule product (diacetone alcohol). At elevated temperatures, this alcohol is dehydrated for releasing of water to form mesityl oxide. Mesityl oxide can undergo subsequent condensation steps to form di-enone, or cyclic isophorone. Theoretically, this reaction could continue with further substitutions on the terminal methyl groups due to its conjugated nature. So, further condensation reaction with another free acetone molecule (unadsorbed state), the conjugated nature of the enone product allows the forming higher molecular weight species that can accumulate in the 464
pore channel, thus restricting access to the active sites and shutting down the reaction (Stevens, 1999). In the internal pore channels of ZSM-5, at high temperatures (Zaki et. al., 2) the decomposition of adsorbed mesitylene oxide or the cracking of diacetone alcohol (Chang, 1981) are susceptible to occur resulting C 3 -C 4 hydrocarbons. Subsequently, the formation of the aromatic compounds can proceed through condensation-dehydrocyclization (Chang et. al., 1981), or through dimerization (Marchionna et al., 21) and alkylation (Albright, 23) these products such as isobutylene We have reported in the previous study (Setiadi, 23) the activity of H-ZSM-5 catalyst with Si/Al ratio=25 is very high with 1 % conversion at 673 K within 2 hrs. Based on these results, this report presents the results of acetone conversion on various temperature and the effect of Si/Al ratio on the longer time of stream. N 2 gas Flow meter Preheater Electric furnace (1W) N 2 Pump fed by pump liquid drop Quartz sand Mixture of ZSM-5 & quartz sand Stainless steel rod Materials and Methods The reaction of acetone conversion was carried out using fixed bed reactor under the atmospheric pressure (Figure 1). The detail of this experimental work has been described elsewhere (Setiadi et al., 23). The acetone was introduced into the reactor by pumping, and the nitrogen was used as carrier gas. The oil-liquid products is collected by cold trap and the ethanol absorption submerged in the ice-water. And the gaseous product was taken by gas bag. The detail of experimental condition is shown in the Table 1. The weight of catalyst was 1 gram. To fix the catalyst in the reactor, 5 gram of quartz sand was mixed this catalyst weight to avoid excessive increase of pressure drop. Liquid product were analyzed by GC-FID and the gaseous products were detected by TCD. Table 1 Detail of Experimental condition Item Data in detail Catalyst : H-ZSM-5 Origin N.E. Chemcat Si/Al ratio : 25, 75, 1 Particle size (dp) : 3 µmeter Catalyst weight : 1 gram for reaction test Quartz sand for : 5 gram (1-15 mesh) blending Quartz sand for : 7 gram (1-15 mesh) preheating Aceton (Cica) : min 99.5% purity Carrier Gas : N 2 Ice - water bath Gaseous product Figure 1 Schematic diagram of experimental set- up for acetone conversion Results and Discussion Effect of Temperature The change of catalyst activity is mainly commonly attributed by the extent of acetone conversion obtained from the reaction at the temperature performed. In order to find the optimum temperature for obtaining the high activity and stability of ZSM-5 for Si/Al ratio of 25, the reaction of acetone conversion was done on the various temperature 723 K, 673 K, 623 K and 573 K. As shown at Figure 2, the activity of H-ZSM-5 catalyst on the temperatures lower than 673 K is not good, the acetone conversion was rapid decreases on shorter time on stream of reaction. The temperature condition higher that 673 K, the activity and stability of ZSM-5 shown a little bit higher. However, as shown in Figure 3 the yield or selectivity of aromatic product found were lower than that of reaction temperature done on 673 K. Accordingly, it is can concluded that the temperature reaction of 673 K is a favourable temperature for conversion of acetone toward aromatics formation. 465
Conversion [wt%] 1 9 8 7 6 5 4 3 2 1 5 1 15 2 25 3 723 K 673 K 623 K 573 K Figure 2 The change of catalytic activity on various reaction temperature over H-ZSM-5 using Si/Al =25 product, but also depends on the surface acidity or acid strength for the acetone reaction. Therefore, the next results present the effect of Si/Al on the activity. Trimethylnaphthalene Dimethylnaphthalene 1-Methylnaphthalene 2-Methylnaphthalene Naphthalene C9-Aromatics o-xylene m+p-xylene Ethylbenzene Toluene Benzene C5~C6 aliphatics C4 aliphatics Diaromatik Monoaromatik C3H8 Monoaromatic yield [wt%] 1 8 6 4 2 5 1 15 2 25 3 Figure 3 The change of monoaromatic yields on various reaction temperature over H-ZSM- 5 using Si/Al =25 Product Distribution 723 K 673 K 623 K 573 K Figure 4 presents the product distribution within 1 min by selectivity of % carbon calculated. It shown that the main monoaromatic product are benzene, toluene, ethyl benzene, m+p-xylene, o- xylene and C 9 -aromatic, and the small amount of naphthalene derivatives compounds. But, the gaseous products are also formed such as CO, CO 2, CH 4, C 2 H 4, C 2 H 6, C 3 H 6, C 3 H 8. Among the component of gaseous products, the quantity of light alkanes (C 3 -C 4 ) was shown in the significant amount. The high selectivity of mono-aromatic product indicate that H-ZSM-5 is very selective for the formation of this product. It can be considered that the pore opening of ZSM-5 is very close to the geometrical molecular size of the aromatic compounds, so that the very high probability of aromatization of acetone occur in the internal surface of channel pore structure. But the activity of H-ZSM- 5 is not only on its abilities to shape the product selectivity toward benzene-ring hydrocarbons Figure 4 The product distribution as the result of acetone conversion at 673 Kafter 4 min using H-ZSM-5 (Si/Al=25) Effect of Si/Al Ratio The result of reaction test is presented by acetone conversion as the indicator performance of catalytic activity of H-ZSM-5 catalyst during the time on stream of reaction up to 1 h. As seen at Figure 5, there was a big difference between Conversion [%] 1 8 6 4 2 C3H6 C2H6 C2H4 CH4 CO2 CO Alifatik 1 2 3 4 Selectivity (% carbon) 2 4 6 8 1 Figure 5 The change of acetone conversion during 1 hours of reaction for the each Si/Al ratio of H-ZSM-5 at 673 K. Symbol : Si/Al=25 ( ), Si/Al=75 ( ) dan Si/Al=1 ( ) 466
Si/Al ratio of 25 and the others ratio (75 or 1). The activity and as well as stability of Si/Al ratio of 25 exhibited the stability during 1 hours of reaction. The activity of H-ZSM-5 with this Si/Al ratio was stable at 1 % conversion. However, the both linecurves for Si/Al ratio 75 and 1 showed the same trend, acetone conversion decreases monotonously along with reaction proceeded. Commonly, the higher Si/Al ratio containing H-ZSM-5 the tendency of acid amount of this zeolite is lower. This result suggested that the activity and stability of H-ZSM-5 catalyst for the acetone conversion is strong correlation with surface acid density of ZSM-5. The yield for hydrocarbon mono-aromatic for each Si/Al ratio is seen at Figure 6. It is obviously shown that yields of aromatic hydrocarbons from acetone conversion using Si/Al=25 were obtained more than 6 %. Yield [% carbon] 1 8 6 4 2 2 4 6 8 1 Figure 6 The change of yield of monoaromatic hydrocarbons during 1 hours of reaction for the each Si/Al ratio of H-ZSM-5 at 673 K. Symbol : Si/Al=25 ( ), Si/Al=75 ( ) dan Si/Al=1 ( ) Apparently, The high selectivity of monoaromatic product indicates the H-ZSM-5 is shape selective catalyst due to its pore structure with pore opening,56 nm and able to suppress the formation the poly-aromatic compound due to the geometrical size of pore. In such pore dimension, the monoaromatic molecule may have a capability to wriggle out from the pore channel of ZSM-5. But, it is likely that the progress of acetone conversion is paralleled with the progress of deactivation. Currently, the main causes of deactivation is convinced of the formation of coke, which was covered or blocked on the surface of H-ZSM-5 catalyst. This is due to the change of physical state between fresh and used catalysts. The study on the confirmation of deactivation is still under progressing such as the change of surface area measurements, the change coke identification, SEM, the change of acidity of used and fresh catalysts. The presence of water in the reactant feed One more interesting result is the reaction of acetone conversion due to the presence of water in the reactant feed. The addition of water into the acetone feed was also carried out to find the its effect on the activity and selectivity of HZSM-5. This work is done due to the much water in the mixture of acetone and MEK in real product from biomass conversion particularly the liquid product resulted from fermentation process(lucas et al., 21. The other effect is if the reaction of acetone conversion can be carried out in the existence of water, the high input energy for separation process of acetone fermented product can be reduced significantly. Table 2 conversion using H-ZSM-5 catalyst under presence and absence of water in the feed Reactant feed +(5 %) H 2 O Temperature (K) 673 673 673 Pressure (MPa).13.13.13 SV acetone (h -1 ) 2.18 4.74 4.32 Conversion (%) 98.1 98.4 99.1 Selected Products (%mol Carbon) Total aromatics 69. 75. 68. Monoaromatics 63.3 71.2 64. Benzene 6.34 4.69 4.6 Toluene 23.8 21.41 19.6 Xylene 22.5 24.2 22.5 It is clearly shown in the Table 2, the result of reaction under the presence of water as much as 5 wt % in the feed is shown in in column 4. Interestingly, the acetone conversion and product selectivity of selected product (aromatic compound) in the presence and without water in the acetone feed is quite similar. This result indicates that the aromatization of acetone over HZSM-5 can proceed even in the existence of water and the aromatisation process can be simplified. Conclusions The change of catalytic activity of H-ZSM-5 catalyst on acetone conversion has been performed by the reaction test on same condition during the time on stream. The time on stream reaction test, 673 K is a favorable temperature for acetone conversion toward aromatic products. The lower temperatures of reaction lead to rapid deactivation, and the higher 467
temperatures tend to decline the yield/selectivity of aromatics products And the time on stream reaction test within 1 h was also found that H-ZSM-5 with Si/Al = 25 is the high active and stable than the Si/Al ratio, it indicates that the reaction of acetone conversion required the high acid density. The presence of water in reactant feed, the no significance changes of activity of H-ZSM-5 on acetone conversion and aromatic product selectivity. References Chang, C.D. & J.S Anthony, 1977. The Conversion of Methanol and Other O-Compounds to Hydrocarbons over Zeolites Catalysts. J. Catalysis 47: 249-259. Chang, Clarence D., W. H. Lang, and W.K. Bell, 1981. Molecular Shape-Selective Catalysis in Zeolite, p.73-94 in Catalysis of Organic Reactions edited by William R. Moser, Marcel Dekker Inc. Gibbs, D.F. 1983. The rise and fall ( and rise?) of acetone/butanol fermentations, Trends in Biotechnology I No. 1 : 12. Haggstrom, L., 1985. -Butanol Fermentation And Its Variants. Biotech Advs 3 :13-28. Lucas, A., P. Canizares, A.Duran. 21. Improving deactivation behaviour of HZSM-5 catalysts. App.Catal. A : General, 26 : 87-93. Lucas, A., P. Canizares, A. Duran and A. Carrero, 1997. Coke Formation, Location, nature and regeneration on Dealuminated HZSM-5 type Zeolites. Applied Catalysis A : General 56 : 299-317. Marcilly, C. 23. Present status and future trends in Catalysis for refining and Petrochemicals. Journal of Catalysis 216: 47 62. Richardson, James T., 1989. Principles of Catalyst Development, Plenum Press, New York. Sie, S.T., 21. Consequences of catalyst deactivation for process design and operation. Applied Catalysis A: General 212: 129 151 Setiadi S., T.Kojima, and T. Tsutsui, 23. Conversion of acetone to aromatic chemical. Journal of the Institute of Energy 82 : 926-932. Setiadi, 25. Konversi Katalitik Aseton menjadi Hidrokarbon C 1 - C 1 menggunakan Katalis ZSM-5 p13. In Prosiding Simposium dan Kongres Masyarakat Katalis Indonesia, Serpong, Indonesia. Stevens, Mark G., Denise Chen dan Henry C. F. 1999. Solid-base catalysts with highly dispersed active sites. Chemical Commun.: 275-276 Xu, M., Wei Wang and Michael Hunger. 23. Formation of acetone enol on acidic zeolite ZSM- 5 evidenced by H/D exchange. Chem Commun : 722-723 Xu, Teng, Eric J Munson,., and Haw, James F. 1994. Toward a Systematic Chemistry of Organic Reactions in Zeolites: In Situ NMR Studies of Ketones. J. Am. Chem. Soc.,116: 1962-1972 Zaki, M.I., M.A.,Hasan, Al-Sagheer dan Pasupulety. 2. Surface chemistry of acetone on metal oxides: IR observation of acetone adsorption and consequent surface reaction on Silica-Alumina vs. Silica and Alumina. Langmuir 16: 43-436 468