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Propylene conversion in Ferrierite: Effect of mesoporous formation
Accepted Manuscript Title: Propylene conversion in Ferrierite: Effect of mesoporous formation Authors: Marcelo Maciel Pereira, Alessandra Vieira, Evandro Brum Pereira, Luciana Rego Monteiro dos Santos, Yiu Lau Lam PII: DOI: Reference:
S0926-860X(17)30313-7 http://dx.doi.org/doi:10.1016/j.apcata.2017.07.013 APCATA 16318
To appear in:
Applied Catalysis A: General
Received date: Revised date: Accepted date:
9-5-2017 4-7-2017 10-7-2017
Please cite this article as: Marcelo Maciel Pereira, Alessandra Vieira, Evandro Brum Pereira, Luciana Rego Monteiro dos Santos, Yiu Lau Lam, Propylene conversion in Ferrierite: Effect of mesoporous formation, Applied Catalysis A, Generalhttp://dx.doi.org/10.1016/j.apcata.2017.07.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Propylene conversion in Ferrierite: Effect of mesoporous formation
Marcelo Maciel Pereira1*, Alessandra Vieira1, Evandro Brum Pereira2, Luciana Rego Monteiro dos Santos3 and Yiu Lau Lam3
1 Laboratório de Catálise e Energia Sustentável, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil * [email protected]
2 Instituto de Química, Departamento de Físico-Química, Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, RJ, Brazil
3 Centro de Pesquisa e Desenvolvimento Leopoldo A. Miguez de Mello – Cenpes/Petrobrás
Graphical abstract
Highlights
Ferrierite zeolite (FER) is active for further transformation of propylene under atmospheric pressure,
It is very selective to products contending six or more carbons and not to other light olefins and light hydrocarbons.
An alkaline treatment remarkable improved both the amount of acid sites and the mesoporous.
The catalytic activity per unit mass of the parent FER was readily improved by mesoporous.
Mesoporous improved the selective to gasoline.
Abstract The formation and subsequent transformation of light olefins is a crucial subject to optimize the production and use of this important intermediate in refining and petrochemical industry. Here a ferrierite zeolite and its mesoporous derivatives obtained by caustic post-treatment (meso-FER) were tested in the transformation of propylene in a flow reactor under atmospheric pressure. The catalysts were compared at iso conversion and characterized by textural, chemical composition and n-hexane cracking. The higher the area of the mesoporous, the higher was the initial catalytic activity for propylene conversion and the selectivity to products containing six or more carbons. Similar results are observed by increasing the propylene partial pressure. Notably, meso-FER formed high amounts of mono-aromatics and branched olefins in the gasoline range, thus improved the gasoline octane number. Moreover, improving the mesoporous area hindered the formation of heavy products. However,
propylene conversion showed a plateau limited to 25-30%. In contrast, other zeolites such as ZSM-5, Beta, and USY tested under the same conditions did not show conversion limitation. In contrast, all these later zeolites were less selective to monoaromatics compared to FER. We proposed that this limitation was probably a result of the narrow canals the FER structure that limited the type of products formed coupled with the constrain imposed by the thermodynamic equilibrium between feed and permissible products inside the zeolite.
Key-words: Ferrierite, mesoporous, propylene, gasoline, zeolites
1 – Introduction
Propylene is one of the most valuable light olefins, raw material for the petrochemical industry. To have better knowledge and hence be able to influence its formation and further transformation is key to improve the operation of relevant refinery processes, such as fluid catalytic cracking (FCC) [1] and those devoted to olefin oligomerization reactions [2, 3]. Indeed, the FCC and related processes have now played an increasing important role in the production of propylene relative to the classical process of steam cracking [4]. Additives containing ZSM-5 zeolites are successfully used to enhance the production of propylene and light olefins in general in FCC and are now widely employed by industry [5-7]. Yet, ferrierite (FER), a zeolite with one-dimensional pore for the purpose of transformation of hydrocarbons, has been cited as the zeolite most selective for light olefins[8]; even though it is much lower in activity than fresh ZSM5 zeolites. Both the lower activity of FER and the higher selectivity in olefins
compared to ZSM-5 is rationalized by its narrow and one-dimensional pore channels by the authors. Even though the FER zeolite has been mentioned in the literature for production of light olefins in cracking of naphtha and related compounds [9-12], its main industrial application is in the isomerization of 1-butene [13]. Recently, Bastiani and co-workers [14], explored the use of FER in severe FCC conditions where the use of only ZSM-5 zeolites as additives to FCC catalysts reached a plateau in the light olefin production. The use of FER combined with ZSM-5 zeolite in these conditions resulted in a higher light olefin production than using ZSM-5 zeolite alone, lifting the plateau. Very high amount of FER had not been tested: due to low activity of FER, the overall catalytic activity of the catalyst system with high amount of FER additive may be too low to be of interest. The authors also attribute the positive effect of FER in the case of high light olefin production to the narrow pore channel of FER. This could limit the bi-molecular hydrogen transfer reactions that could consume molecules such as propylene by transforming it to propane. To obtain more information on the conversion of propylene over FER zeolites, in this work, we examine propylene conversion in the presence of FER under total atmospheric pressure. The temperature, partial pressure of propylene and the contact time were chosen that allow the information readily extrapolated to FCC conditions. Some typical zeolites of wider pore structures such as ZSM-5, beta and Y zeolite were also tested under the same conditions for comparison. Finally, to enhance the activity of FER, we also explored the creation of more external surface area of FER by caustic leaching. The treatment procedure was adopted from the literature without optimization [15].
2 – Experimental Ferrierite (FER-1) was a commercially purchased zeolite. FER-2 was obtained by caustic post-treatment in FER-1 using diluted NaOH (0.35M), with 6.6 % solid at 80 °C during 180 minutes, and FER-3 was obtained by using NaOH (0.35M), with 3.3% solid at 100 °C during 180 minutes. All zeolites were then exhaustively exchanged with NH4Cl, washed with water and thermally treated in a furnace in air at 500oC during 3 hours. These ferrierite zeolites were compared to ZSM-5, d-ZSM-5 (obtained by treatment of the fresh ZSM5 already mentioned in steam, total pressure 1 atm, at 700oC during 3 h), Beta and USY. Textural characterization was carried out in ASAP2050M instruments (Micromeritics, USA) for BET surface area, mesopore surface area, and micropore volume. The nitrogen physical adsorption-desorption isotherms were measured at 77 K. The high precision pressure measurements were achieved by the low-pressure transducer with the capacity of 0.1 Torr. The specific surface area, BET, was evaluated from the nitrogen adsorption isotherm in the range of relative pressure p/ p0 = 0.05–0.25, p is the adsorbate pressure (at equilibrium condition), and p0 is the initial adsorbate vapor pressure at the measuring temperature) using the standard Brunauer– Emmett–Teller (BET) procedure [16]. Both silicon and aluminum amount in wt.% were determined by X-Ray Fluorescence (XRF) by an analyzer Phillips, model PW 2400. X-ray Diffraction (XRD) was performed using a Rigaku Ultima IV diffractometer (Cu Kα λ =0.1542 nm) at a scanning rate of 0.02o s-1 in 2 θ ranges from 5 to 80o. A fixed power source was used (40 kV, 20 mA). N-Hexane cracking experiments were performed in a high throughput unit. Eight tubular quartz reactors assembled in parallel to each other (187 mm in length and 6 mm internal diameter) were used. After cationic exchange and thermal
treatment, H—FER and other zeolites for comparison were activated under nitrogen at 500°C for 2 h before catalytic evaluation. Then the flow was shifted to an 11 %v/v of n-hexane in nitrogen (60 mL/min). The products were injected online after 3, 17 and 32 min on stream using a GC-2010 Shimadzu chromatograph. The set-up details, as well as chromatographic conditions, were already reported elsewhere[17]. The activity was presented as the average result obtained at 17 and 32 min on stream (Table S1). Even though minor deactivation was observed (the catalytic rate differs by less than 5% between the first injection at 2 min and the last one at 32 min), the results did not interfere the comparison of the zeolites (Table S1). Propylene conversion experiments were carried out in a fixed bed unit using a tubular reactor made of stainless steel. Before the reaction, the catalyst was heated in a nitrogen flow (60 mL/min) from room temperature to 500oC and kept at this temperature for one hour. Then, at 500°C, mixtures of propylene and nitrogen at atmospheric pressure and total flow 60mL/min, were converted in the presence of the catalysts. The following propylene partial pressures were used: 0.2, 0.3 and 0.5 atm. The catalyst weight was adjusted to obtain similar propylene conversion among the catalysts (from a practical point, this can be considered as iso-conversion conditions for all tests). Additionally, for some test conditions, the amount of catalyst was increased. Typically, the gas effluent was analyzed after 10 minutes of time on stream (TOS) and all catalysts were compared at this same TOS. Also, to observe the deactivation as a function of time on stream, propylene reaction was carried out in the presence of FER-3 at reaction times up to 3, 10, 30, 55 and 75 minutes (each catalytic run provided one reaction time). Additionally, for FER-2 and FER-3, long duration tests (90 min) were carried out to collect the liquid product to be characterized more fully to identify the main products present in the liquid fraction. In these cases, the gas
effluent was first past through a trap in an ice bath before analysis. The selectivity is the ratio of products weighted by the carbon number, i.e . %Mi x i / summation of % Mj x j , I and j are the number of carbons ans j is all products including i , but not propylene) of the different products, according to the expression 1. The condensed liquid product was processed as follow. The analysis of the gasoline fraction: the products distribution was performed on a 6890 Agilent Technologies gas chromatograph equipped with a FID detector. The chromatograph was equipped with a separator to eliminate the compounds heavier than gasoline and a PONA capillary column (L: 50 m; ID: 0.2 mm; Film: 0.5 µm). For the analyses, 0.5 µL of sample was injected, with a split ratio of 1:40. The GC oven temperature ranged from 0 ˚C to 180 ˚C. The liquid products theoretical distillation was carried out by the SIMDIS method (ASTM 2887), using a 6890 gas chromatograph from Agilent Technologies equipped with a FID detector. The GC was equipped with an Ultra-1 capillary column (L: 25 m; ID: 0.2 mm; Film: 0.11 µm) and hydrogen (1 mL/min) as vector gas. A liquid sample volume of 0.5 µL was used, with a split ratio of 1:150, and oven temperature range from 50 to 325 ˚C, at a heating rate of 20 ˚C/min. The gasoline, LCO and Heavy fractions were determined by previous injection of hydrocarbon standards and grouped in the following fraction: gasoline (boiling point up to 216oC), LCO (boiling point between 216 and 343 oC), and Bottom (remaining liquid compounds).
3 – Results 3.1 Catalyst Properties
The main properties of the ferrierite zeolites, ZSM-5, Beta and USY zeolites are presented in Table 1. The XRD diffraction are presented in figure 1 and all catalysts showed XRD diffraction of the ferrierite, the FER-2 showed a slight decrease in the intensity compared to FER-1; a further decrease in the FER-3 XRD intensity was observed. The FER-1 showed typical mesoporous (meso)- and BETareas as compared with reported in the literature [14]. The meso area in FER-2 increased 3.85-fold and the microporous volume reduced 17% comparing with FER1. For FER-3 compared with FER-1 these values increased 7.1-fold and reduced 25% respectively. Thus, the increase in meso area did not correspond to a straight-line correlation with the decrease in the micropore volume, as presented in figure S1. In addition, the BET area of FER-3 increased 19 % compared to FER-1. These features could be related to improving porous diffusion, by removing extra framework species of silicon and aluminum (EFSi, EFAL). The improving in meso area by alkaline hydrolysis is related in the literature to silicon leaching [15], thus resulting in a decreasing the silica/alumina mole ratio (SAR). The SAR of ferrierite was estimated by the measuring the silica leached from these preparations in the solution remained, and 19 and 52% of silica was removed in FER-2 and FER-3 compared to that in the parent FER. Hence the SAR could be estimated for these meso FER zeolites. This implied much higher number active sites per gram of FER-3 as compared to the original FER. This difference has to be taken into account in the subsequent discussion of activity and selectivity of the catalytic tests. The n-hexane activity as a function of time on stream differs by less than 5% for ferrierite catalysts as shown in table S1 and the catalytic activity was estimated by the average of two tests as presented in table S2. Ferrierite zeolites were less active in n-hexane cracking compared to that of fresh ZSM-5 and Beta zeolites, but the catalyst
d-ZSM-5 showed similar activity compared to FER catalysts as shown in Table1. Among ferrierites, FER-3 showed the highest n-hexane activity, and the following order for n-hexane activity was observed FER
3.2 Propylene conversion and catalytic activity
The evidence that reaction tests were carried out in the kinetic regime and the condition to attain the iso-conversion for all catalysts are presented in Figure 2 (at partial pressure 0.5 atm balance in nitrogen, total flow 60 mLmin-1 at 500°C). The data of d-ZSM-5 (discussed later after FER catalysts) shows that the conversion of C3= continually increased up to 70%. Such high conversion of olefins was already reported to ZSM-5. However, crystal size, SAR and distribution of Brønsted site all play an important role in the propylene conversion [2]. As further support, at 70% conversion, a two-fold increase in both the amount of catalyst and the reactant flow resulted in the same conversion, as presented in figure S2. This definitively proved that the tests are with no external diffusion limitation and that kinetic regime is observed up to high conversion. Also, larger pore zeolite like Beta did not show conversion limitation as presented in Table 2. By contrast, the FER-3 catalyst showed a plateau type behavior in the propylene conversion when the amount of FER-3 was increased. This type-plateau in the conversion of propylene was also verified in reactor with larger diameter (as shown in Table S3). The FER has narrow and one-dimensional channel for practical diffusion [8]. This could limit the cracking of the oligomers, such as n-hexene formed. Indeed, nhexene is reverted to propylene when cracked over FER. While on ZSM-5 n-hexene is cracked to olefins containing 2, 3 and 4 carbons. Thus, with high pressure of the feeding propylene (C3=), C3= and hexene come to equilibrium concentration and no further C3= conversion will be observed unless hexene is converted to other products, such as cyclic products. This cyclization is probably slow in the channel of FER, and in particular a slower process as compared to oligomerization. Hence, one observed a limitation on the C3= conversion rate in practice in these conditions. For ZSM-5,
both the light olefins distributions to compounds containing 2, 3 and 4 carbons and the cyclization rate due to larger channel size (and also the secondary channel) will let the C3= conversion surpass this limit for FER. Thus, in short, the FER structure could limited the type of products formed coupled with the constraint imposed by the thermodynamic equilibrium between feed and permissible products inside the zeolite. The propylene conversion at 0.5 atm partial pressure with time on stream in the presence of FER-3 is presented in figure S3 and a slight deactivate was observed. This deactivation is related to coke formation, as by applying regeneration in air, the activity was restored by 90% as presented in Table S4. The results of the catalytic reaction rate for propylene at 0.2, 0.3 and 0.5 atm partial pressure, TOS=10 min and 500oC are presented in Table 2. As explained in the experimental section, the mass of catalyst was adjusted to obtain similar conversion, thus both catalyst activity and selectivity could be better compared among the catalysts. With the propylene partial pressure at 0.5 atm the FER-1 catalyst showed a catalytic rate of 1154 µmol gcat min-1, this value remarkably increased 4-fold and 7fold for FER-2 and FER-3 catalysts respectively. Similar tendencies were observed at 0.3 and 0.2 atm of propylene. Therefore, for all propylene partial pressure, the activity follows the order FER-3>FER-2>FER. However, at the same propylene partial pressure, both FER-2 and FER-3 showed very similar TOF in corresponding tests, both very superior when compared to that in FER-1. For each catalyst the catalytic activity and TOF was normalized by the respective values at 0.2 atm, these values are presented in figures 3 -a and -b respectively. The normalized catalytic activity was remarkably similar for both FER-2 and FER-3, also the propylene catalytic rate was adjusted by a first order correlation. The normalized TOF follow the same tendency. The lower angular coefficient observed for FER-1 suggest that
diffusion limitation in the channel of FER-1 should be more important compared to that in both FER-2 and -3. Clearly, the higher the propylene partial pressure, the higher the catalytic activity for all ferrierites. There are two possible explanations for the fact that the rate increases with partial pressure. First, the adsorption of the olefins on the zeolite are not that strong. They were not “attracted” naturally to the sites and had to be forced. Thus, for example, the oligomerization of olefins in the presence of ZSM-5 is practiced in a pressure range of 20-70 bar and temperature in the range of 200- 300oC and resulted in mainly olefins formations [20, 21]. Indeed, at room temperature, the experimental observation of wall adsorption of 1-butene is dependent on the accessibility of π-electrons to the brønsted acid sites, thus resulting in larger energy barrier in ZSM-5 compared to Mordenite. And in ferrierite, the adsorption of 1-butene is hinder at low temperature [22]. Second, the basicity of the π C-C bond is superior to that of σ C-C bond; thus the double bond of propylene is readily protonated compared to the σ C-C bond of nhexane. For instance1-hexene cracks 230 times faster than n-hexane at 538oC[23]. Here the TOF values of propylene are highly superior to that of n-hexane for all FER catalysts. Generally, oligomerization reaction involves meeting of more than one molecules and increase in pressure should help in these. However, the narrow and unidimensional pores of FER improves the contribution of bimolecular reaction, probably between carbenions species and propylene and may have hindered that the rate increase even more dramatically with pressure than first order The catalytic activity was also correlated with the meso porous area as presented in Figure 4. As can be seen, a remarkable straight-line correlation with meso area and activity was found. Also, very low activity (57 – 224 µmol propylene
g-1 (cat) min-1) would be expected for FER with negligible meso area (by extrapolating the linear adjust in figure 4 to zero meso area). The above discussion suggests that even if some changing in the amount of strong acid sites such as from FER-2 compared to that in FER-3 (from the TOF in the n-hexane test) occurs this did not significantly affect the propylene conversion. Thus, in olefin conversion, the topology and textural properties should be the main important features rather than the type of the acids sites.
3.3 Effect of catalyst on the selectivity
The selectivity of propylene derived products was presented as follow: the SC6+ represents the products containing six and more carbons atoms, butenes and pentenes are grouped in (SC=4-5), butanes as SC4 and propane as SC3. These values are presented in figures 5 -a and –b respectively. The conversion of propylene at 0.2 atm in the presence of FER catalyst showed a SC=4-5 fraction and SC6+ selectivity of 0.11 and 0.86 respectively. The increase in the propylene partial pressure decreased the SC=4-5 and increased the SC6+ selectivity. The same tendency was observed for both FER-2 and FER-3 catalysts, but the presence of mesoporous increased the SC6+ selectivity with a corresponding decrease in the SC=4-5 selectivity. For instance, propylene was converted in the presence of FER-3 forming almost exclusively SC6+ selectivity of 0.98 at 0.3 atm propylene partial pressure. The same SC6+ selectivity was observed in propylene conversion at a higher pressure 0.5 atm in the presence of FER-2 with a smaller amount of mesopores. These results show the effect of mesoporous on the product selectivity in the propylene conversion. Also, due to the
small unidimensional pores of FER, the oligomerization would be limited to a certain size, thus controlling the type and the amount of products in the SC6+ fraction. Further, the mesoporous catalyst can work at high propylene partial pressure without an excessive coke or large products formation. A superior performance of FER-3 in propylene conversion compared FER-2, could be related to both the meso area and the type of acidity, i.e. the improved diffusion in large pores released intermediate products (mainly light oligomers) that are not sequentially cracked in FER-3 as it does not have too much strong acid sites compared to FER-2. Detail distributions of SC6+ for both FER-2 and FER-3 in the test carried out during 90 min of TOS are presented in Table 3. The FER-2 was highly selective to gasoline fraction, which was composed mainly of mono-alkyl-aromatic, branched olefins (BO) and naphthenic compounds. With FER-3 the aromatic formation and the naphthenic were slightly reduced, while BO increased in 50%. Further, FER-3 showed lower bottom formation compared to that in FER-2 catalyst. This is probably a result of improving diffusion of intermediate products, avoiding their further alkylation. Therefore, the FER-3 catalysts showed improvements in both the yield and the octane number of the gasoline compared with FER-2. To summarize the SC6+ selectivity increases by increasing the mesoporous area and increasing propylene partial pressure, while ethylene, butenes, and pentenes decrease. Propylene is firstly protonated on acid sites to originate a proponium cation. Then, a biomolecular reaction such as dimerization followed by a combination of isomerization, cyclization and hydrogen transfer (HT) reactions [3, 24] produces several products in SC6+ fraction including mono-aromatic formation. Sequentially, the cracking (or re-conversion) of NP, BO, NO and naphthenics in SC6+ fraction
produces SC=4-5 fraction. Some hydrogen transfer reaction also resulted in the formation of propane. In addition to the reactions aforementioned, reactions involving coke formation also take place [25-27], contributing to the catalytic deactivation. Interestingly, the high BO concentration in FER-3 compared with FER-2 could be a consequence of improving the diffusivity. Likewise, the slight decrease in naphthenics and aromatics that are produced by sequential reaction (like cyclization and aromatization for example) could also be a consequence of improved diffusivity. Naturally, further improvement on gasoline could be achieved by optimizing the zeolite properties and process condition. However, for now, it is clear that of both mesoporous and propylene partial pressure are responsible for the high selectivity for gasoline production. This fraction is remarkably rich in aromatic, thus avoiding a subsequent hydrotreatment as required for the products from the typical MOGD process that is highly concentrated in olefins. 3.4 Comparing FER, ZSM-5, deactivated ZSM-5, Beta and USY zeolites: the pore structure constrain on further reaction of oligomers The selectivity and propylene conversion for all catalysts (in different conversion regime by changing the catalyst amount) are presented in Table 4. Increasing the propylene conversion in the presence of FER-3 (entrance 7 and 8) resulted in no significant changing in SC6+, a further increasing in the conversion (to 30%) reduces this selectivity to 87% (entrance 9). In contrast, both ZSM-5 and dZSM-5 showed SC6+ at iso conversion (at 16%) at 83 and 70% respectively. These are lower values compared with FER-3. The selectivity of d-ZSM-5 was determined in a great range of conversion as presented in figure 6. The continuous reconversion of SC6+ into pentenes and butenes was previously reported [27], thus three main conversion regime was proposed,
oligomerization producing a high amount of SC6+ at low conversion, an intermediary cracking of oligomers followed by hydrogen transfer reaction at high conversion. This reaction scheme as a function of conversion was not found in FER. We proposed that this difference was due to the narrow and one-dimensional pores of FER, limiting the size of the oligomers and the mode of further cracking of the oligomers. Beta zeolite showed similar conversion (and activity) to FER-1 catalysts and yet similar products selectivity as d-ZSM-5 (entrances 3 and 10 respectively). USY showed the worst SC6+ selectivity and the highest propane formation and besides, high butenes and pentenes selectivity, thus the permitted products undergoes sequential and excessive cracking reaction that resulted in light products formation and high deactivation (by Coke) as presented in figure S5. The conversion of olefin in the presence of ZSM-5 is widely studied in the literature [2, 24, 28]. In general, olefins oligomerize to products that are sequentially cracked. The products distribution is affected by the amount of acid sites, pore structure, and textural properties. The comparison of fresh ZSM-5 and deactivated ZSM-5 (d-ZSM-5) for two chosen conversions are presented in table 4. At isoconversion around 9% it was observed a slight increase in the SC=4-5 and a slight decreased in the SC6+ fractions using d-ZSM-5 instead of fresh ZSM-5. At 15% isoconversion, further SC=4-5 increase with the corresponding reduction in SC6+ for dZSM-5 compared to those values in ZSM-5 were observed. Also a slight increase in ethane and propane was observed in the presence of the former zeolite. These results suggest that products containing nine carbons atoms should be the main intermediate of oligomerization of propylene (in the presence of ZSM-5) that further reacts producing olefins containing four and fine carbons.
4 – Discussion: insight on propylene conversion (and products reconversion) in function of the topology and textural properties of zeolites.
Examining the transformation of propylene on FER and comparing its behavior with typical zeolites such as ZSM-5, beta and USY, we obtained information on the interplay between the pore structure and propylene transformation that is important for application for optimizing propylene production and use. First, even with the restricted pore opening, FER is active for further transformation of propylene under atmospheric pressure, generating oligomers. FER is very selective to C6+ products and not to other light olefins and light hydrocarbons. Cyclization and further hydrogen transfer occurred leading to aromatics. Gasoline range products were mainly formed as a result of both the test condition and the pore structure. Second, the activity per unit mass of the parent FER was readily improved by alkaline treatment. This could be due to a combined effect of increasing the active site per mass of zeolite because of silica removal from the framework and the increase in accessibility to the active sites due to the formation of mesopores. Nevertheless, the selectivity of transformation showed clearly that the decrease of products of further transformation of oligomers of propylene, such as light olefins and aromatics. This provided evidence of the effect of accessibility as a consequence of the creation of mesoporosity. Third, the conversion of propylene over FER reached a limit while under the same conditions the conversion over ZSM-5 was way above this level. This important observation could be rationalized by the domination of pore structure on further conversion of the oligomers formed. For ZSM-5 zeolite, oligomers of olefins
reconverted or cracked to form a mixture of C2, C3, C4 and C5 olefins aside from cyclization and hydrogen transfer to aromatics. However, due to the straight canal pore structure of FER, olefin oligomer did not convert readily in different light olefins. This was supported by the distribution of the light olefin products. Typically, for example, mono-molecular cracking of n-hexene may only revert this molecule to propylene again. Consequently, the concentrations of propylene and hexene came to equilibrium. No further transformation of propylene to hexene could occur unless hexene is converted to other products, probably by slower reaction rate.
5 – Conclusion Ferrierite transforms propylene readily under atmospheric pressure and at rather high temperature of 500 °C to products mainly in the gasoline range. Its activity was improved by improving its mesoporous area and volume, and the selectivity to gasoline range products also increased. These results were consistent with the increase in the accessibility of the active sites of FER due to mesopore formation. However, a conversion limitation was observed under the testing conditions employed for FER with improving the mesoporous area. Distinct from other zeolites such as ZSM-5. We proposed that this may be due to a high rate and selective recracking of oligomers such as hexenes back to propylene, creating an equilibrium situation between the reactant and products. This result is quite specific to the narrow and one-dimensional pore structure of FER.
6 – Acknowledgment Marcelo Maciel Pereira thanks and informs that it was a great privilege to have been guided by both Martin Schmal and Yiu Lau Lam during his Ph.D thesis.
7 - References [1] E.T.C. Vogt, G.T. Whiting, A.D. Chowdhury, B.M. Weckhuysen, Zeolites and Zeotypes for Oil and Gas Conversion, elsevier2015. [2] A. Corma, C. Martínez, E. Doskocil, Designing MFI-based catalysts with improved catalyst life for C3= and C5=, Oligomerization to high-quality liquid fuels, jounal of catalysis, 300 (2013) 183–196. [3] R.J. Quam, L.A. Green, S.A. Tabak, F.J. Krambeck, Chemistry of Olefin Oligomerization over ZSM-5 Catalyst, Ind. Eng. Chem. Res., 27 (1988) 565-570. [4] A. Farshi, F. Shaiyegh, S.H. Burogerdi, A. Dehgan, FCC Process Role in Propylene Demands, Petroleum Science and Technology, 29 (2011) 875-885. [5] S.J. Miller, C.R. Hsieh, Octane Enhancement in Catalytic Cracking by Using High-Silica Zeolites, in: M.L. Occelli (Ed.) Fluid Catalytic Cracking II. Concepts in Catalyst DesignAmerican Chemical Society, 1991, pp. 96-108. [6] J.S. Buchanan, Gasoline selective ZSM-5 FCC additives Model reactions of C6-C10 olefins over steamed ZSM-5, Applied Catalysis a-General, 171 (1998) 57-64. [7] R.J. Mandon, Role of ZSM-5 and Ultrastable Y Zeolites for Increasing Gasoline Octane Number, jounal of catalysis, 129 (1991) 275-287. [8] B.G. Anderson, R.R. Schumacher, R.v. Duren, A.P. Singh, R.A.v. Santen, An attempt to predict the optimum zeolite based catalyst forselective cracking of naphtha-range hydrocarbons to light olefins, Journal of Molecular Catalysis A: Chemical, 181 (2002) 291–301. [9] H. Abrevaya, Cracking of naphtha range alkanes and naphthenes over zeolites, Studies in Surface Science and CAtalysis, 170 (2007) 1244-1251. [10] O. Bortnovsky, P. Sazama, B. Wichterlova, Cracking of pentenes to C2–C4 light olefins over zeolites and zeotypes Role of topology and acid site strength and concentration, 287 (2005) 203–213. [11] T. Komatsu, Hisaya Ishihara, Y. Fukui, T. Yashima, Selective formation of alkenes through the cracking of n-heptane on Ca2+-exchanged ferrierite, Applied catalysis A: general, 214 (2001) 103–109. [12] A. Corma, V. González-Alfaro, A.V. Orchillés, The role of pore topology on the behaviour of FCC zeolite additives, Applied Catalysis A:General, 187 (1999) 245–254. [13] W.-Q. Xu, Y.-G. Yin, S.L. Suib, J.C. Edwards, C.-L. O’Young, Modification of Nontemplate Synthesized Ferrierite/ZSM-35 for n-Butene Skeletal Isomerization to Isobutylene, jounal of catalysis, 163 (1996) 232–244. [14] R. Bastiani, Y.L. Lam, C.A. Henriques, V.T.d. Silva, Application of ferrierite zeolite in high-olefin catalytic cracking, Fuel, 107 (2013) 680–687. [15] A. Bonilla, D. Baudouin, J. Pérez-Ramírez, Desilication of ferrierite zeolite for porosity generation and improved, journal os Catalysis, 265 (2009) 170–180. [16] S. Brunauer, P.H. Emmett, E. Teller, Adsorption of gases in multimolecular layers, Am. Chem. Soc., 60 (1938) 309-319. [17] A.J. Maia, B. Louis, Y.L. Lam, M.M. Pereira, Ni-ZSM-5 catalysts: Detailed characterization of metal sites for proper catalyst design, Journal of Catalysis, 269 (2010) 103-109. [18] A.D.F. Ferreira, A.J. Maia, B. Guatiguaba, M.H. Herbst, P.T.L. Rocha, M.M. Pereira, B. Louis, Nickel-doped small pore zeolite bifunctional catalysts: A way to achieve high activity and yields into olefins, Catalysis Today, 226 (2014) 67-72. [19] B. Louis, M.M. Pereira, F.M. Santos, P.M. Esteves, J. Sommer, Alkane activation over acidic zeolites: the first step, Chemistry, 16 (2010) 573-578. [20] M.L. Occelli, J.T. Hsu, L.G. Galya, Propylene oligomerization over molecular sieves part I. Zeolite effects on reactivity and liquid product selectivities, Journal of molecular catalysis, 32 (1985) 377-390.
[21] G. Bellussi, F. Mizia, V. Calemma, P. Pollesel, R. Millini, Oligomerization of olefins from Light Cracking Naphtha over zeolite-based catalyst for the production of high quality diesel fuel, Microporous and Mesoporous Materials, 164 (2012) 127-134. [22] E. Yoda, J.N. Kondo, K. Domen, Detailed Process of Adsorption of Alkanes on Zeolites, J. Phys. Chem. B, 109 (2005) 1464-1472. [23] R.J. Mandon, Role of ZSM-5 and Ultrastable Y Zeolites for Increasing Gasoline, Journal of Catalysis, 129 (1991) 275-287. [24] D. Liu, W.C. Choi, N.Y. Kang, Y.J. Lee, H.S. Park, C.-H. Shin, Y.-K. Park, Interconversion of light olefins on ZSM-5 in catalytic naphtha cracking condition, Catalysis Today, 226 (2014) 52-66. [25] M. Bjørgen, Coke precursor formation and zeolite deactivation: mechanistic insights from hexamethylbenzene conversion, Journal of Catalysis, 215 (2003) 30-44. [26] M. Occelli, The Location and Effects of Coke Deposition in Fluid Cracking Catalysts during Gas Oil Cracking at Microactivity Test Conditions, Journal of Catalysis, 209 (2002) 385-393. [27] M.F. Reyniers, Y. Tang, G.B. Marin, Influence of coke formation on the conversion of hydrocarbons: II. i-Butene on HY-zeolites, Applied Catalysis A: General, 202 (2000) 6580. [28] A. Coelho, G. Caeiro, M.A.N.D.A. Lemos, F. Lemos, F.R. Ribeiro, 1-Butene oligomerization over ZSM-5 zeolite: Part 1 – Effect of reaction conditions, Fuel, 111 (2013) 449-460.
Figures
5
3.5x10
4
5.0x10 u
5
3.0x10
5
Intensity
2.5x10
FER-1
5
2.0x10
5
1.5x10
FER-2 5
1.0x10
FER-3
4
5.0x10
0.0 10
20
2
30
40
Figure 1: X-ray diffraction of ferrierite catalysts, the diffraction lines of ferrierite based on ICDD number 00-044-0104 are indicated in the bottom of the figure.
.
n-hexane conversion %
70 60 50 40 30 20 10 0 0
50 100 mass of the catalyst (mg)
150
Figure 2: Propylene conversion versus the amount of (o) FER-3 and (☐) d-ZSM-5 catalysts showing a plateau-type conversion for FER-3 (propylene partial pressure 0.5 atm balance in nitrogen, total flow 60 mLmin-1 at 500°C).
Figure 3: a) The catalytic rate normalized, for each catalyst the catalytic activity (μmol of propene converted gcat-1min-1) was normalized by the respective values at 0.2 atm. b) Normalized TOF, for each catalyst the TOF (calculate by dividing the μmol of Propene converted gcat-1min-1 by total aluminum content) was normalized by
the respective values at 0.2 atm.
Figure 4: The catalytic rate of Propylene at 500oC, propylene partial pressure 0.2-0.5 atm versus the meso area for all ferrierites zeolites adjusted by first order fits accord to the following equations: 58.23 X + 57.795 (R2=0.999), 18.81 X + 224.06 (R2=0.9888), 5.63X + 139.81 (R2=0.9995) for propylene at 0.5, 0.3 and 0.2 respectively.
Figure 5: Selectivity for a) heavier than six carbons (S6+) and b) butenes and pentenes (C4-5) at 500o C versus the propylene partial pressure 0.2-0.5 atm for all ferrierites zeolites.
Figure 6: Selectivity of products grouped by fraction in the Propylene reaction in the presence of d-ZSM-5, C5, and C4 includes saturate and unsaturated compounds containing five and four carbons, and SC6+ includes all compounds with six or more carbons.
Table 1: Main features of the catalysts Catalyst
Na2O, ppm 400
BET, m2g-1 350
Ext. meso area m2g-1
Vmicro, mLg-1
FER-1
molar SiO2/Al2O3 54
Cat. C3/C3= Rate
20
0.135
99
0.57
FER-2
44*
600
346
77
0.111
219
0.46
FER-3
24*
300
415
142
0.101
247
0.43
f-ZSM5
27
< 500
370
20
0.125
5745
0.39
d-ZSM5
n.d.
309
n.d.
0.090
173
0.22
BETA
27
300
574
204
0.167
4000
0.86
USY
30
300
605
n.d.
0.28
80
0.41
ppm < 500 ppm
molar SiO2/Al2O3: composition of silica and alumina express in molar ratio, Na2O, ppm : sodium amount in ppm Vmicro : volume of micropores Cat. Rate : n-hexane conversion rate in µmol n- hexane converted gcat-1 min-1 C3/C3=: Propane/Propylene ratio in wt.% * estimated from material balance from chemical analysis of leached solution
Table 2: Results of Propylene reaction
mass
Pressure Flow Flow Conv. Cat. TOF C3= N2 Propylene Rate (min-1) (mg) (atm) (mL/min) (mL/min) (%) FER-1 130 0.5 30 30 11.2 1154 3.9 FER-1 164.8 0.3 42 18 10.8 525 1.8 FER-1 225 0.2 48 12 10.8 257 0.9 FER-2 30.2 0.5 30 30 10.5 4670 12.8 FER-2 61.7 0.3 42 18 13.9 1813 5.0 FER-2 100.8 0.2 48 12 10.6 565 1.5 FER-3 19.2 0.5 30 30 11.9 8266 12.7 FER-3 29.8 0.3 42 18 10.5 2829 4.4 FER-3 71.9 0.2 48 12 12.7 943 1.5 Cat. Rate : µmol propylene converted g.cat-1min-1, TOF calculated by dividing Cat. Rate by the aluminum amount derived from the SAR value.
Table 3: Product distribution in wt.% of liquid fraction for FER-2 and FER-3 (reaction conditions are propylene partial pressure at 0.5 atm., temperature 500o C and total flow of propylene and nitrogen 60 mlmin-1).
FER-2 FER-3 Composition of the gasoline fraction, in wt % NP, Normal paraffins
1.31
0.67
BP, Branched paraffins
5.87
5.79
olefins
6.74
5.49
BO, Branched olefins
17.72
26.80
TN, Total naphthenics
15.35
11.92
AR, Total Aromatics
49.26
47.17
MON**
84
87
Distribution of the liquid fraction in wt. % * Gasoline
91.07
97.08
LCO
2.46
2.45
Bottom
6.47
0.47
* The fractions obtained were: Gasoline (boiling point up to 216oC), LCO (boiling point between 216 and 343 oC), and Bottom (remaining liquid compounds). **MON is calculated from the composition of the gasoline.
Table 4: Propylene catalytic test* in the presence of ferrierites, ZSM-5, Beta and USY zeolites, conversion (Conv.), selectivity in wt. % for ethylene, propane, butanes, butenes, pentenes and compounds containing six and more carbons are SC2=, SC3, Sc4, SC4=, SC5=, SC6+ respectively.
Catalyst 1 2 3
(mg) Conv. (%) SC2= SC3 Sc4 SC4= SC5= SC6+
d-ZSM-5 12.2 ZSM-5
2
d-ZSM-5 25.2
9.6
0.3
0.4 NF
3
4
92
8.4
0.2
0.4 NF
3
3
94
16.2
0.7
0.4 NF
8
8
83
0.4 NF
5
5
89
NF
4
2
93
4
ZSM-5
3
15.73
0.3
5
FER-1
130
11.24
1
6
FER-2
30
10.53
NF
NF NF
2
NF
98
7
FER-3
19
11.90
NF
NF NF
1
NF
98
8
FER-3
31
17
0.4
0.3 NF
2
1
97
9
FER -3
141
30
1
1
0.1
6
5
87
10
BETA
133
14.04
1
3
0.5
8
6
82
11
USY**
278
8.92
4
62
NF
14
4
5
1
NF not found * (reaction conditions are propylene partial pressure at 0.5 atm., temperature 500o C and total flow of propylene and nitrogen 60 mlmin-1) ** USY showed high deactivation by coke as presented in figure S5.
S0926-860X(17)30313-7 http://dx.doi.org/doi:10.1016/j.apcata.2017.07.013 APCATA 16318
To appear in:
Applied Catalysis A: General
Received date: Revised date: Accepted date:
9-5-2017 4-7-2017 10-7-2017
Please cite this article as: Marcelo Maciel Pereira, Alessandra Vieira, Evandro Brum Pereira, Luciana Rego Monteiro dos Santos, Yiu Lau Lam, Propylene conversion in Ferrierite: Effect of mesoporous formation, Applied Catalysis A, Generalhttp://dx.doi.org/10.1016/j.apcata.2017.07.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Propylene conversion in Ferrierite: Effect of mesoporous formation
Marcelo Maciel Pereira1*, Alessandra Vieira1, Evandro Brum Pereira2, Luciana Rego Monteiro dos Santos3 and Yiu Lau Lam3
1 Laboratório de Catálise e Energia Sustentável, Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil * [email protected]
2 Instituto de Química, Departamento de Físico-Química, Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, RJ, Brazil
3 Centro de Pesquisa e Desenvolvimento Leopoldo A. Miguez de Mello – Cenpes/Petrobrás
Graphical abstract
Highlights
Ferrierite zeolite (FER) is active for further transformation of propylene under atmospheric pressure,
It is very selective to products contending six or more carbons and not to other light olefins and light hydrocarbons.
An alkaline treatment remarkable improved both the amount of acid sites and the mesoporous.
The catalytic activity per unit mass of the parent FER was readily improved by mesoporous.
Mesoporous improved the selective to gasoline.
Abstract The formation and subsequent transformation of light olefins is a crucial subject to optimize the production and use of this important intermediate in refining and petrochemical industry. Here a ferrierite zeolite and its mesoporous derivatives obtained by caustic post-treatment (meso-FER) were tested in the transformation of propylene in a flow reactor under atmospheric pressure. The catalysts were compared at iso conversion and characterized by textural, chemical composition and n-hexane cracking. The higher the area of the mesoporous, the higher was the initial catalytic activity for propylene conversion and the selectivity to products containing six or more carbons. Similar results are observed by increasing the propylene partial pressure. Notably, meso-FER formed high amounts of mono-aromatics and branched olefins in the gasoline range, thus improved the gasoline octane number. Moreover, improving the mesoporous area hindered the formation of heavy products. However,
propylene conversion showed a plateau limited to 25-30%. In contrast, other zeolites such as ZSM-5, Beta, and USY tested under the same conditions did not show conversion limitation. In contrast, all these later zeolites were less selective to monoaromatics compared to FER. We proposed that this limitation was probably a result of the narrow canals the FER structure that limited the type of products formed coupled with the constrain imposed by the thermodynamic equilibrium between feed and permissible products inside the zeolite.
Key-words: Ferrierite, mesoporous, propylene, gasoline, zeolites
1 – Introduction
Propylene is one of the most valuable light olefins, raw material for the petrochemical industry. To have better knowledge and hence be able to influence its formation and further transformation is key to improve the operation of relevant refinery processes, such as fluid catalytic cracking (FCC) [1] and those devoted to olefin oligomerization reactions [2, 3]. Indeed, the FCC and related processes have now played an increasing important role in the production of propylene relative to the classical process of steam cracking [4]. Additives containing ZSM-5 zeolites are successfully used to enhance the production of propylene and light olefins in general in FCC and are now widely employed by industry [5-7]. Yet, ferrierite (FER), a zeolite with one-dimensional pore for the purpose of transformation of hydrocarbons, has been cited as the zeolite most selective for light olefins[8]; even though it is much lower in activity than fresh ZSM5 zeolites. Both the lower activity of FER and the higher selectivity in olefins
compared to ZSM-5 is rationalized by its narrow and one-dimensional pore channels by the authors. Even though the FER zeolite has been mentioned in the literature for production of light olefins in cracking of naphtha and related compounds [9-12], its main industrial application is in the isomerization of 1-butene [13]. Recently, Bastiani and co-workers [14], explored the use of FER in severe FCC conditions where the use of only ZSM-5 zeolites as additives to FCC catalysts reached a plateau in the light olefin production. The use of FER combined with ZSM-5 zeolite in these conditions resulted in a higher light olefin production than using ZSM-5 zeolite alone, lifting the plateau. Very high amount of FER had not been tested: due to low activity of FER, the overall catalytic activity of the catalyst system with high amount of FER additive may be too low to be of interest. The authors also attribute the positive effect of FER in the case of high light olefin production to the narrow pore channel of FER. This could limit the bi-molecular hydrogen transfer reactions that could consume molecules such as propylene by transforming it to propane. To obtain more information on the conversion of propylene over FER zeolites, in this work, we examine propylene conversion in the presence of FER under total atmospheric pressure. The temperature, partial pressure of propylene and the contact time were chosen that allow the information readily extrapolated to FCC conditions. Some typical zeolites of wider pore structures such as ZSM-5, beta and Y zeolite were also tested under the same conditions for comparison. Finally, to enhance the activity of FER, we also explored the creation of more external surface area of FER by caustic leaching. The treatment procedure was adopted from the literature without optimization [15].
2 – Experimental Ferrierite (FER-1) was a commercially purchased zeolite. FER-2 was obtained by caustic post-treatment in FER-1 using diluted NaOH (0.35M), with 6.6 % solid at 80 °C during 180 minutes, and FER-3 was obtained by using NaOH (0.35M), with 3.3% solid at 100 °C during 180 minutes. All zeolites were then exhaustively exchanged with NH4Cl, washed with water and thermally treated in a furnace in air at 500oC during 3 hours. These ferrierite zeolites were compared to ZSM-5, d-ZSM-5 (obtained by treatment of the fresh ZSM5 already mentioned in steam, total pressure 1 atm, at 700oC during 3 h), Beta and USY. Textural characterization was carried out in ASAP2050M instruments (Micromeritics, USA) for BET surface area, mesopore surface area, and micropore volume. The nitrogen physical adsorption-desorption isotherms were measured at 77 K. The high precision pressure measurements were achieved by the low-pressure transducer with the capacity of 0.1 Torr. The specific surface area, BET, was evaluated from the nitrogen adsorption isotherm in the range of relative pressure p/ p0 = 0.05–0.25, p is the adsorbate pressure (at equilibrium condition), and p0 is the initial adsorbate vapor pressure at the measuring temperature) using the standard Brunauer– Emmett–Teller (BET) procedure [16]. Both silicon and aluminum amount in wt.% were determined by X-Ray Fluorescence (XRF) by an analyzer Phillips, model PW 2400. X-ray Diffraction (XRD) was performed using a Rigaku Ultima IV diffractometer (Cu Kα λ =0.1542 nm) at a scanning rate of 0.02o s-1 in 2 θ ranges from 5 to 80o. A fixed power source was used (40 kV, 20 mA). N-Hexane cracking experiments were performed in a high throughput unit. Eight tubular quartz reactors assembled in parallel to each other (187 mm in length and 6 mm internal diameter) were used. After cationic exchange and thermal
treatment, H—FER and other zeolites for comparison were activated under nitrogen at 500°C for 2 h before catalytic evaluation. Then the flow was shifted to an 11 %v/v of n-hexane in nitrogen (60 mL/min). The products were injected online after 3, 17 and 32 min on stream using a GC-2010 Shimadzu chromatograph. The set-up details, as well as chromatographic conditions, were already reported elsewhere[17]. The activity was presented as the average result obtained at 17 and 32 min on stream (Table S1). Even though minor deactivation was observed (the catalytic rate differs by less than 5% between the first injection at 2 min and the last one at 32 min), the results did not interfere the comparison of the zeolites (Table S1). Propylene conversion experiments were carried out in a fixed bed unit using a tubular reactor made of stainless steel. Before the reaction, the catalyst was heated in a nitrogen flow (60 mL/min) from room temperature to 500oC and kept at this temperature for one hour. Then, at 500°C, mixtures of propylene and nitrogen at atmospheric pressure and total flow 60mL/min, were converted in the presence of the catalysts. The following propylene partial pressures were used: 0.2, 0.3 and 0.5 atm. The catalyst weight was adjusted to obtain similar propylene conversion among the catalysts (from a practical point, this can be considered as iso-conversion conditions for all tests). Additionally, for some test conditions, the amount of catalyst was increased. Typically, the gas effluent was analyzed after 10 minutes of time on stream (TOS) and all catalysts were compared at this same TOS. Also, to observe the deactivation as a function of time on stream, propylene reaction was carried out in the presence of FER-3 at reaction times up to 3, 10, 30, 55 and 75 minutes (each catalytic run provided one reaction time). Additionally, for FER-2 and FER-3, long duration tests (90 min) were carried out to collect the liquid product to be characterized more fully to identify the main products present in the liquid fraction. In these cases, the gas
effluent was first past through a trap in an ice bath before analysis. The selectivity is the ratio of products weighted by the carbon number, i.e . %Mi x i / summation of % Mj x j , I and j are the number of carbons ans j is all products including i , but not propylene) of the different products, according to the expression 1. The condensed liquid product was processed as follow. The analysis of the gasoline fraction: the products distribution was performed on a 6890 Agilent Technologies gas chromatograph equipped with a FID detector. The chromatograph was equipped with a separator to eliminate the compounds heavier than gasoline and a PONA capillary column (L: 50 m; ID: 0.2 mm; Film: 0.5 µm). For the analyses, 0.5 µL of sample was injected, with a split ratio of 1:40. The GC oven temperature ranged from 0 ˚C to 180 ˚C. The liquid products theoretical distillation was carried out by the SIMDIS method (ASTM 2887), using a 6890 gas chromatograph from Agilent Technologies equipped with a FID detector. The GC was equipped with an Ultra-1 capillary column (L: 25 m; ID: 0.2 mm; Film: 0.11 µm) and hydrogen (1 mL/min) as vector gas. A liquid sample volume of 0.5 µL was used, with a split ratio of 1:150, and oven temperature range from 50 to 325 ˚C, at a heating rate of 20 ˚C/min. The gasoline, LCO and Heavy fractions were determined by previous injection of hydrocarbon standards and grouped in the following fraction: gasoline (boiling point up to 216oC), LCO (boiling point between 216 and 343 oC), and Bottom (remaining liquid compounds).
3 – Results 3.1 Catalyst Properties
The main properties of the ferrierite zeolites, ZSM-5, Beta and USY zeolites are presented in Table 1. The XRD diffraction are presented in figure 1 and all catalysts showed XRD diffraction of the ferrierite, the FER-2 showed a slight decrease in the intensity compared to FER-1; a further decrease in the FER-3 XRD intensity was observed. The FER-1 showed typical mesoporous (meso)- and BETareas as compared with reported in the literature [14]. The meso area in FER-2 increased 3.85-fold and the microporous volume reduced 17% comparing with FER1. For FER-3 compared with FER-1 these values increased 7.1-fold and reduced 25% respectively. Thus, the increase in meso area did not correspond to a straight-line correlation with the decrease in the micropore volume, as presented in figure S1. In addition, the BET area of FER-3 increased 19 % compared to FER-1. These features could be related to improving porous diffusion, by removing extra framework species of silicon and aluminum (EFSi, EFAL). The improving in meso area by alkaline hydrolysis is related in the literature to silicon leaching [15], thus resulting in a decreasing the silica/alumina mole ratio (SAR). The SAR of ferrierite was estimated by the measuring the silica leached from these preparations in the solution remained, and 19 and 52% of silica was removed in FER-2 and FER-3 compared to that in the parent FER. Hence the SAR could be estimated for these meso FER zeolites. This implied much higher number active sites per gram of FER-3 as compared to the original FER. This difference has to be taken into account in the subsequent discussion of activity and selectivity of the catalytic tests. The n-hexane activity as a function of time on stream differs by less than 5% for ferrierite catalysts as shown in table S1 and the catalytic activity was estimated by the average of two tests as presented in table S2. Ferrierite zeolites were less active in n-hexane cracking compared to that of fresh ZSM-5 and Beta zeolites, but the catalyst
d-ZSM-5 showed similar activity compared to FER catalysts as shown in Table1. Among ferrierites, FER-3 showed the highest n-hexane activity, and the following order for n-hexane activity was observed FER
3.2 Propylene conversion and catalytic activity
The evidence that reaction tests were carried out in the kinetic regime and the condition to attain the iso-conversion for all catalysts are presented in Figure 2 (at partial pressure 0.5 atm balance in nitrogen, total flow 60 mLmin-1 at 500°C). The data of d-ZSM-5 (discussed later after FER catalysts) shows that the conversion of C3= continually increased up to 70%. Such high conversion of olefins was already reported to ZSM-5. However, crystal size, SAR and distribution of Brønsted site all play an important role in the propylene conversion [2]. As further support, at 70% conversion, a two-fold increase in both the amount of catalyst and the reactant flow resulted in the same conversion, as presented in figure S2. This definitively proved that the tests are with no external diffusion limitation and that kinetic regime is observed up to high conversion. Also, larger pore zeolite like Beta did not show conversion limitation as presented in Table 2. By contrast, the FER-3 catalyst showed a plateau type behavior in the propylene conversion when the amount of FER-3 was increased. This type-plateau in the conversion of propylene was also verified in reactor with larger diameter (as shown in Table S3). The FER has narrow and one-dimensional channel for practical diffusion [8]. This could limit the cracking of the oligomers, such as n-hexene formed. Indeed, nhexene is reverted to propylene when cracked over FER. While on ZSM-5 n-hexene is cracked to olefins containing 2, 3 and 4 carbons. Thus, with high pressure of the feeding propylene (C3=), C3= and hexene come to equilibrium concentration and no further C3= conversion will be observed unless hexene is converted to other products, such as cyclic products. This cyclization is probably slow in the channel of FER, and in particular a slower process as compared to oligomerization. Hence, one observed a limitation on the C3= conversion rate in practice in these conditions. For ZSM-5,
both the light olefins distributions to compounds containing 2, 3 and 4 carbons and the cyclization rate due to larger channel size (and also the secondary channel) will let the C3= conversion surpass this limit for FER. Thus, in short, the FER structure could limited the type of products formed coupled with the constraint imposed by the thermodynamic equilibrium between feed and permissible products inside the zeolite. The propylene conversion at 0.5 atm partial pressure with time on stream in the presence of FER-3 is presented in figure S3 and a slight deactivate was observed. This deactivation is related to coke formation, as by applying regeneration in air, the activity was restored by 90% as presented in Table S4. The results of the catalytic reaction rate for propylene at 0.2, 0.3 and 0.5 atm partial pressure, TOS=10 min and 500oC are presented in Table 2. As explained in the experimental section, the mass of catalyst was adjusted to obtain similar conversion, thus both catalyst activity and selectivity could be better compared among the catalysts. With the propylene partial pressure at 0.5 atm the FER-1 catalyst showed a catalytic rate of 1154 µmol gcat min-1, this value remarkably increased 4-fold and 7fold for FER-2 and FER-3 catalysts respectively. Similar tendencies were observed at 0.3 and 0.2 atm of propylene. Therefore, for all propylene partial pressure, the activity follows the order FER-3>FER-2>FER. However, at the same propylene partial pressure, both FER-2 and FER-3 showed very similar TOF in corresponding tests, both very superior when compared to that in FER-1. For each catalyst the catalytic activity and TOF was normalized by the respective values at 0.2 atm, these values are presented in figures 3 -a and -b respectively. The normalized catalytic activity was remarkably similar for both FER-2 and FER-3, also the propylene catalytic rate was adjusted by a first order correlation. The normalized TOF follow the same tendency. The lower angular coefficient observed for FER-1 suggest that
diffusion limitation in the channel of FER-1 should be more important compared to that in both FER-2 and -3. Clearly, the higher the propylene partial pressure, the higher the catalytic activity for all ferrierites. There are two possible explanations for the fact that the rate increases with partial pressure. First, the adsorption of the olefins on the zeolite are not that strong. They were not “attracted” naturally to the sites and had to be forced. Thus, for example, the oligomerization of olefins in the presence of ZSM-5 is practiced in a pressure range of 20-70 bar and temperature in the range of 200- 300oC and resulted in mainly olefins formations [20, 21]. Indeed, at room temperature, the experimental observation of wall adsorption of 1-butene is dependent on the accessibility of π-electrons to the brønsted acid sites, thus resulting in larger energy barrier in ZSM-5 compared to Mordenite. And in ferrierite, the adsorption of 1-butene is hinder at low temperature [22]. Second, the basicity of the π C-C bond is superior to that of σ C-C bond; thus the double bond of propylene is readily protonated compared to the σ C-C bond of nhexane. For instance1-hexene cracks 230 times faster than n-hexane at 538oC[23]. Here the TOF values of propylene are highly superior to that of n-hexane for all FER catalysts. Generally, oligomerization reaction involves meeting of more than one molecules and increase in pressure should help in these. However, the narrow and unidimensional pores of FER improves the contribution of bimolecular reaction, probably between carbenions species and propylene and may have hindered that the rate increase even more dramatically with pressure than first order The catalytic activity was also correlated with the meso porous area as presented in Figure 4. As can be seen, a remarkable straight-line correlation with meso area and activity was found. Also, very low activity (57 – 224 µmol propylene
g-1 (cat) min-1) would be expected for FER with negligible meso area (by extrapolating the linear adjust in figure 4 to zero meso area). The above discussion suggests that even if some changing in the amount of strong acid sites such as from FER-2 compared to that in FER-3 (from the TOF in the n-hexane test) occurs this did not significantly affect the propylene conversion. Thus, in olefin conversion, the topology and textural properties should be the main important features rather than the type of the acids sites.
3.3 Effect of catalyst on the selectivity
The selectivity of propylene derived products was presented as follow: the SC6+ represents the products containing six and more carbons atoms, butenes and pentenes are grouped in (SC=4-5), butanes as SC4 and propane as SC3. These values are presented in figures 5 -a and –b respectively. The conversion of propylene at 0.2 atm in the presence of FER catalyst showed a SC=4-5 fraction and SC6+ selectivity of 0.11 and 0.86 respectively. The increase in the propylene partial pressure decreased the SC=4-5 and increased the SC6+ selectivity. The same tendency was observed for both FER-2 and FER-3 catalysts, but the presence of mesoporous increased the SC6+ selectivity with a corresponding decrease in the SC=4-5 selectivity. For instance, propylene was converted in the presence of FER-3 forming almost exclusively SC6+ selectivity of 0.98 at 0.3 atm propylene partial pressure. The same SC6+ selectivity was observed in propylene conversion at a higher pressure 0.5 atm in the presence of FER-2 with a smaller amount of mesopores. These results show the effect of mesoporous on the product selectivity in the propylene conversion. Also, due to the
small unidimensional pores of FER, the oligomerization would be limited to a certain size, thus controlling the type and the amount of products in the SC6+ fraction. Further, the mesoporous catalyst can work at high propylene partial pressure without an excessive coke or large products formation. A superior performance of FER-3 in propylene conversion compared FER-2, could be related to both the meso area and the type of acidity, i.e. the improved diffusion in large pores released intermediate products (mainly light oligomers) that are not sequentially cracked in FER-3 as it does not have too much strong acid sites compared to FER-2. Detail distributions of SC6+ for both FER-2 and FER-3 in the test carried out during 90 min of TOS are presented in Table 3. The FER-2 was highly selective to gasoline fraction, which was composed mainly of mono-alkyl-aromatic, branched olefins (BO) and naphthenic compounds. With FER-3 the aromatic formation and the naphthenic were slightly reduced, while BO increased in 50%. Further, FER-3 showed lower bottom formation compared to that in FER-2 catalyst. This is probably a result of improving diffusion of intermediate products, avoiding their further alkylation. Therefore, the FER-3 catalysts showed improvements in both the yield and the octane number of the gasoline compared with FER-2. To summarize the SC6+ selectivity increases by increasing the mesoporous area and increasing propylene partial pressure, while ethylene, butenes, and pentenes decrease. Propylene is firstly protonated on acid sites to originate a proponium cation. Then, a biomolecular reaction such as dimerization followed by a combination of isomerization, cyclization and hydrogen transfer (HT) reactions [3, 24] produces several products in SC6+ fraction including mono-aromatic formation. Sequentially, the cracking (or re-conversion) of NP, BO, NO and naphthenics in SC6+ fraction
produces SC=4-5 fraction. Some hydrogen transfer reaction also resulted in the formation of propane. In addition to the reactions aforementioned, reactions involving coke formation also take place [25-27], contributing to the catalytic deactivation. Interestingly, the high BO concentration in FER-3 compared with FER-2 could be a consequence of improving the diffusivity. Likewise, the slight decrease in naphthenics and aromatics that are produced by sequential reaction (like cyclization and aromatization for example) could also be a consequence of improved diffusivity. Naturally, further improvement on gasoline could be achieved by optimizing the zeolite properties and process condition. However, for now, it is clear that of both mesoporous and propylene partial pressure are responsible for the high selectivity for gasoline production. This fraction is remarkably rich in aromatic, thus avoiding a subsequent hydrotreatment as required for the products from the typical MOGD process that is highly concentrated in olefins. 3.4 Comparing FER, ZSM-5, deactivated ZSM-5, Beta and USY zeolites: the pore structure constrain on further reaction of oligomers The selectivity and propylene conversion for all catalysts (in different conversion regime by changing the catalyst amount) are presented in Table 4. Increasing the propylene conversion in the presence of FER-3 (entrance 7 and 8) resulted in no significant changing in SC6+, a further increasing in the conversion (to 30%) reduces this selectivity to 87% (entrance 9). In contrast, both ZSM-5 and dZSM-5 showed SC6+ at iso conversion (at 16%) at 83 and 70% respectively. These are lower values compared with FER-3. The selectivity of d-ZSM-5 was determined in a great range of conversion as presented in figure 6. The continuous reconversion of SC6+ into pentenes and butenes was previously reported [27], thus three main conversion regime was proposed,
oligomerization producing a high amount of SC6+ at low conversion, an intermediary cracking of oligomers followed by hydrogen transfer reaction at high conversion. This reaction scheme as a function of conversion was not found in FER. We proposed that this difference was due to the narrow and one-dimensional pores of FER, limiting the size of the oligomers and the mode of further cracking of the oligomers. Beta zeolite showed similar conversion (and activity) to FER-1 catalysts and yet similar products selectivity as d-ZSM-5 (entrances 3 and 10 respectively). USY showed the worst SC6+ selectivity and the highest propane formation and besides, high butenes and pentenes selectivity, thus the permitted products undergoes sequential and excessive cracking reaction that resulted in light products formation and high deactivation (by Coke) as presented in figure S5. The conversion of olefin in the presence of ZSM-5 is widely studied in the literature [2, 24, 28]. In general, olefins oligomerize to products that are sequentially cracked. The products distribution is affected by the amount of acid sites, pore structure, and textural properties. The comparison of fresh ZSM-5 and deactivated ZSM-5 (d-ZSM-5) for two chosen conversions are presented in table 4. At isoconversion around 9% it was observed a slight increase in the SC=4-5 and a slight decreased in the SC6+ fractions using d-ZSM-5 instead of fresh ZSM-5. At 15% isoconversion, further SC=4-5 increase with the corresponding reduction in SC6+ for dZSM-5 compared to those values in ZSM-5 were observed. Also a slight increase in ethane and propane was observed in the presence of the former zeolite. These results suggest that products containing nine carbons atoms should be the main intermediate of oligomerization of propylene (in the presence of ZSM-5) that further reacts producing olefins containing four and fine carbons.
4 – Discussion: insight on propylene conversion (and products reconversion) in function of the topology and textural properties of zeolites.
Examining the transformation of propylene on FER and comparing its behavior with typical zeolites such as ZSM-5, beta and USY, we obtained information on the interplay between the pore structure and propylene transformation that is important for application for optimizing propylene production and use. First, even with the restricted pore opening, FER is active for further transformation of propylene under atmospheric pressure, generating oligomers. FER is very selective to C6+ products and not to other light olefins and light hydrocarbons. Cyclization and further hydrogen transfer occurred leading to aromatics. Gasoline range products were mainly formed as a result of both the test condition and the pore structure. Second, the activity per unit mass of the parent FER was readily improved by alkaline treatment. This could be due to a combined effect of increasing the active site per mass of zeolite because of silica removal from the framework and the increase in accessibility to the active sites due to the formation of mesopores. Nevertheless, the selectivity of transformation showed clearly that the decrease of products of further transformation of oligomers of propylene, such as light olefins and aromatics. This provided evidence of the effect of accessibility as a consequence of the creation of mesoporosity. Third, the conversion of propylene over FER reached a limit while under the same conditions the conversion over ZSM-5 was way above this level. This important observation could be rationalized by the domination of pore structure on further conversion of the oligomers formed. For ZSM-5 zeolite, oligomers of olefins
reconverted or cracked to form a mixture of C2, C3, C4 and C5 olefins aside from cyclization and hydrogen transfer to aromatics. However, due to the straight canal pore structure of FER, olefin oligomer did not convert readily in different light olefins. This was supported by the distribution of the light olefin products. Typically, for example, mono-molecular cracking of n-hexene may only revert this molecule to propylene again. Consequently, the concentrations of propylene and hexene came to equilibrium. No further transformation of propylene to hexene could occur unless hexene is converted to other products, probably by slower reaction rate.
5 – Conclusion Ferrierite transforms propylene readily under atmospheric pressure and at rather high temperature of 500 °C to products mainly in the gasoline range. Its activity was improved by improving its mesoporous area and volume, and the selectivity to gasoline range products also increased. These results were consistent with the increase in the accessibility of the active sites of FER due to mesopore formation. However, a conversion limitation was observed under the testing conditions employed for FER with improving the mesoporous area. Distinct from other zeolites such as ZSM-5. We proposed that this may be due to a high rate and selective recracking of oligomers such as hexenes back to propylene, creating an equilibrium situation between the reactant and products. This result is quite specific to the narrow and one-dimensional pore structure of FER.
6 – Acknowledgment Marcelo Maciel Pereira thanks and informs that it was a great privilege to have been guided by both Martin Schmal and Yiu Lau Lam during his Ph.D thesis.
7 - References [1] E.T.C. Vogt, G.T. Whiting, A.D. Chowdhury, B.M. Weckhuysen, Zeolites and Zeotypes for Oil and Gas Conversion, elsevier2015. [2] A. Corma, C. Martínez, E. Doskocil, Designing MFI-based catalysts with improved catalyst life for C3= and C5=, Oligomerization to high-quality liquid fuels, jounal of catalysis, 300 (2013) 183–196. [3] R.J. Quam, L.A. Green, S.A. Tabak, F.J. Krambeck, Chemistry of Olefin Oligomerization over ZSM-5 Catalyst, Ind. Eng. Chem. Res., 27 (1988) 565-570. [4] A. Farshi, F. Shaiyegh, S.H. Burogerdi, A. Dehgan, FCC Process Role in Propylene Demands, Petroleum Science and Technology, 29 (2011) 875-885. [5] S.J. Miller, C.R. Hsieh, Octane Enhancement in Catalytic Cracking by Using High-Silica Zeolites, in: M.L. Occelli (Ed.) Fluid Catalytic Cracking II. Concepts in Catalyst DesignAmerican Chemical Society, 1991, pp. 96-108. [6] J.S. Buchanan, Gasoline selective ZSM-5 FCC additives Model reactions of C6-C10 olefins over steamed ZSM-5, Applied Catalysis a-General, 171 (1998) 57-64. [7] R.J. Mandon, Role of ZSM-5 and Ultrastable Y Zeolites for Increasing Gasoline Octane Number, jounal of catalysis, 129 (1991) 275-287. [8] B.G. Anderson, R.R. Schumacher, R.v. Duren, A.P. Singh, R.A.v. Santen, An attempt to predict the optimum zeolite based catalyst forselective cracking of naphtha-range hydrocarbons to light olefins, Journal of Molecular Catalysis A: Chemical, 181 (2002) 291–301. [9] H. Abrevaya, Cracking of naphtha range alkanes and naphthenes over zeolites, Studies in Surface Science and CAtalysis, 170 (2007) 1244-1251. [10] O. Bortnovsky, P. Sazama, B. Wichterlova, Cracking of pentenes to C2–C4 light olefins over zeolites and zeotypes Role of topology and acid site strength and concentration, 287 (2005) 203–213. [11] T. Komatsu, Hisaya Ishihara, Y. Fukui, T. Yashima, Selective formation of alkenes through the cracking of n-heptane on Ca2+-exchanged ferrierite, Applied catalysis A: general, 214 (2001) 103–109. [12] A. Corma, V. González-Alfaro, A.V. Orchillés, The role of pore topology on the behaviour of FCC zeolite additives, Applied Catalysis A:General, 187 (1999) 245–254. [13] W.-Q. Xu, Y.-G. Yin, S.L. Suib, J.C. Edwards, C.-L. O’Young, Modification of Nontemplate Synthesized Ferrierite/ZSM-35 for n-Butene Skeletal Isomerization to Isobutylene, jounal of catalysis, 163 (1996) 232–244. [14] R. Bastiani, Y.L. Lam, C.A. Henriques, V.T.d. Silva, Application of ferrierite zeolite in high-olefin catalytic cracking, Fuel, 107 (2013) 680–687. [15] A. Bonilla, D. Baudouin, J. Pérez-Ramírez, Desilication of ferrierite zeolite for porosity generation and improved, journal os Catalysis, 265 (2009) 170–180. [16] S. Brunauer, P.H. Emmett, E. Teller, Adsorption of gases in multimolecular layers, Am. Chem. Soc., 60 (1938) 309-319. [17] A.J. Maia, B. Louis, Y.L. Lam, M.M. Pereira, Ni-ZSM-5 catalysts: Detailed characterization of metal sites for proper catalyst design, Journal of Catalysis, 269 (2010) 103-109. [18] A.D.F. Ferreira, A.J. Maia, B. Guatiguaba, M.H. Herbst, P.T.L. Rocha, M.M. Pereira, B. Louis, Nickel-doped small pore zeolite bifunctional catalysts: A way to achieve high activity and yields into olefins, Catalysis Today, 226 (2014) 67-72. [19] B. Louis, M.M. Pereira, F.M. Santos, P.M. Esteves, J. Sommer, Alkane activation over acidic zeolites: the first step, Chemistry, 16 (2010) 573-578. [20] M.L. Occelli, J.T. Hsu, L.G. Galya, Propylene oligomerization over molecular sieves part I. Zeolite effects on reactivity and liquid product selectivities, Journal of molecular catalysis, 32 (1985) 377-390.
[21] G. Bellussi, F. Mizia, V. Calemma, P. Pollesel, R. Millini, Oligomerization of olefins from Light Cracking Naphtha over zeolite-based catalyst for the production of high quality diesel fuel, Microporous and Mesoporous Materials, 164 (2012) 127-134. [22] E. Yoda, J.N. Kondo, K. Domen, Detailed Process of Adsorption of Alkanes on Zeolites, J. Phys. Chem. B, 109 (2005) 1464-1472. [23] R.J. Mandon, Role of ZSM-5 and Ultrastable Y Zeolites for Increasing Gasoline, Journal of Catalysis, 129 (1991) 275-287. [24] D. Liu, W.C. Choi, N.Y. Kang, Y.J. Lee, H.S. Park, C.-H. Shin, Y.-K. Park, Interconversion of light olefins on ZSM-5 in catalytic naphtha cracking condition, Catalysis Today, 226 (2014) 52-66. [25] M. Bjørgen, Coke precursor formation and zeolite deactivation: mechanistic insights from hexamethylbenzene conversion, Journal of Catalysis, 215 (2003) 30-44. [26] M. Occelli, The Location and Effects of Coke Deposition in Fluid Cracking Catalysts during Gas Oil Cracking at Microactivity Test Conditions, Journal of Catalysis, 209 (2002) 385-393. [27] M.F. Reyniers, Y. Tang, G.B. Marin, Influence of coke formation on the conversion of hydrocarbons: II. i-Butene on HY-zeolites, Applied Catalysis A: General, 202 (2000) 6580. [28] A. Coelho, G. Caeiro, M.A.N.D.A. Lemos, F. Lemos, F.R. Ribeiro, 1-Butene oligomerization over ZSM-5 zeolite: Part 1 – Effect of reaction conditions, Fuel, 111 (2013) 449-460.
Figures
5
3.5x10
4
5.0x10 u
5
3.0x10
5
Intensity
2.5x10
FER-1
5
2.0x10
5
1.5x10
FER-2 5
1.0x10
FER-3
4
5.0x10
0.0 10
20
2
30
40
Figure 1: X-ray diffraction of ferrierite catalysts, the diffraction lines of ferrierite based on ICDD number 00-044-0104 are indicated in the bottom of the figure.
.
n-hexane conversion %
70 60 50 40 30 20 10 0 0
50 100 mass of the catalyst (mg)
150
Figure 2: Propylene conversion versus the amount of (o) FER-3 and (☐) d-ZSM-5 catalysts showing a plateau-type conversion for FER-3 (propylene partial pressure 0.5 atm balance in nitrogen, total flow 60 mLmin-1 at 500°C).
Figure 3: a) The catalytic rate normalized, for each catalyst the catalytic activity (μmol of propene converted gcat-1min-1) was normalized by the respective values at 0.2 atm. b) Normalized TOF, for each catalyst the TOF (calculate by dividing the μmol of Propene converted gcat-1min-1 by total aluminum content) was normalized by
the respective values at 0.2 atm.
Figure 4: The catalytic rate of Propylene at 500oC, propylene partial pressure 0.2-0.5 atm versus the meso area for all ferrierites zeolites adjusted by first order fits accord to the following equations: 58.23 X + 57.795 (R2=0.999), 18.81 X + 224.06 (R2=0.9888), 5.63X + 139.81 (R2=0.9995) for propylene at 0.5, 0.3 and 0.2 respectively.
Figure 5: Selectivity for a) heavier than six carbons (S6+) and b) butenes and pentenes (C4-5) at 500o C versus the propylene partial pressure 0.2-0.5 atm for all ferrierites zeolites.
Figure 6: Selectivity of products grouped by fraction in the Propylene reaction in the presence of d-ZSM-5, C5, and C4 includes saturate and unsaturated compounds containing five and four carbons, and SC6+ includes all compounds with six or more carbons.
Table 1: Main features of the catalysts Catalyst
Na2O, ppm 400
BET, m2g-1 350
Ext. meso area m2g-1
Vmicro, mLg-1
FER-1
molar SiO2/Al2O3 54
Cat. C3/C3= Rate
20
0.135
99
0.57
FER-2
44*
600
346
77
0.111
219
0.46
FER-3
24*
300
415
142
0.101
247
0.43
f-ZSM5
27
< 500
370
20
0.125
5745
0.39
d-ZSM5
n.d.
309
n.d.
0.090
173
0.22
BETA
27
300
574
204
0.167
4000
0.86
USY
30
300
605
n.d.
0.28
80
0.41
ppm < 500 ppm
molar SiO2/Al2O3: composition of silica and alumina express in molar ratio, Na2O, ppm : sodium amount in ppm Vmicro : volume of micropores Cat. Rate : n-hexane conversion rate in µmol n- hexane converted gcat-1 min-1 C3/C3=: Propane/Propylene ratio in wt.% * estimated from material balance from chemical analysis of leached solution
Table 2: Results of Propylene reaction
mass
Pressure Flow Flow Conv. Cat. TOF C3= N2 Propylene Rate (min-1) (mg) (atm) (mL/min) (mL/min) (%) FER-1 130 0.5 30 30 11.2 1154 3.9 FER-1 164.8 0.3 42 18 10.8 525 1.8 FER-1 225 0.2 48 12 10.8 257 0.9 FER-2 30.2 0.5 30 30 10.5 4670 12.8 FER-2 61.7 0.3 42 18 13.9 1813 5.0 FER-2 100.8 0.2 48 12 10.6 565 1.5 FER-3 19.2 0.5 30 30 11.9 8266 12.7 FER-3 29.8 0.3 42 18 10.5 2829 4.4 FER-3 71.9 0.2 48 12 12.7 943 1.5 Cat. Rate : µmol propylene converted g.cat-1min-1, TOF calculated by dividing Cat. Rate by the aluminum amount derived from the SAR value.
Table 3: Product distribution in wt.% of liquid fraction for FER-2 and FER-3 (reaction conditions are propylene partial pressure at 0.5 atm., temperature 500o C and total flow of propylene and nitrogen 60 mlmin-1).
FER-2 FER-3 Composition of the gasoline fraction, in wt % NP, Normal paraffins
1.31
0.67
BP, Branched paraffins
5.87
5.79
olefins
6.74
5.49
BO, Branched olefins
17.72
26.80
TN, Total naphthenics
15.35
11.92
AR, Total Aromatics
49.26
47.17
MON**
84
87
Distribution of the liquid fraction in wt. % * Gasoline
91.07
97.08
LCO
2.46
2.45
Bottom
6.47
0.47
* The fractions obtained were: Gasoline (boiling point up to 216oC), LCO (boiling point between 216 and 343 oC), and Bottom (remaining liquid compounds). **MON is calculated from the composition of the gasoline.
Table 4: Propylene catalytic test* in the presence of ferrierites, ZSM-5, Beta and USY zeolites, conversion (Conv.), selectivity in wt. % for ethylene, propane, butanes, butenes, pentenes and compounds containing six and more carbons are SC2=, SC3, Sc4, SC4=, SC5=, SC6+ respectively.
Catalyst 1 2 3
(mg) Conv. (%) SC2= SC3 Sc4 SC4= SC5= SC6+
d-ZSM-5 12.2 ZSM-5
2
d-ZSM-5 25.2
9.6
0.3
0.4 NF
3
4
92
8.4
0.2
0.4 NF
3
3
94
16.2
0.7
0.4 NF
8
8
83
0.4 NF
5
5
89
NF
4
2
93
4
ZSM-5
3
15.73
0.3
5
FER-1
130
11.24
1
6
FER-2
30
10.53
NF
NF NF
2
NF
98
7
FER-3
19
11.90
NF
NF NF
1
NF
98
8
FER-3
31
17
0.4
0.3 NF
2
1
97
9
FER -3
141
30
1
1
0.1
6
5
87
10
BETA
133
14.04
1
3
0.5
8
6
82
11
USY**
278
8.92
4
62
NF
14
4
5
1
NF not found * (reaction conditions are propylene partial pressure at 0.5 atm., temperature 500o C and total flow of propylene and nitrogen 60 mlmin-1) ** USY showed high deactivation by coke as presented in figure S5.