Effect of phenol adsorption on HY zeolite for n-heptane cracking: Comparison with methylcyclohexane

Applied Catalysis A: General 385 (2010) 178–189

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Effect of phenol adsorption on HY zeolite for n-heptane cracking: Comparison with methylcyclohexane I. Grac¸a a,b , A. Fernandes a , J.M. Lopes a,∗ , M.F. Ribeiro a , S. Laforge b , P. Magnoux b , F. Ramôa Ribeiro a a IBB, Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Técnico - Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b Laboratoire de Catalyse en Chimie Organique, UMR 6503 CNRS - Université de Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers Cedex, France

a r t i c l e

i n f o

Article history: Received 6 April 2010 Received in revised form 8 June 2010 Accepted 6 July 2010 Available online 13 July 2010 Keywords: Bio-oils Catalytic cracking Zeolites n-Heptane transformation Phenol

a b s t r a c t To evaluate the possibility to partially replace the classical Fluid Catalytic Cracking (FCC) feedstocks by bio-oils derived from lignocellulosic biomass, the transformation of n-heptane was performed in the presence of small quantities of phenol over an HY zeolite, at 350 and 450 ◦ C. The results were compared with those previously obtained with methylcyclohexane. Phenol leads to a further deactivation of the zeolite due to phenol adsorption on the Brönsted and Lewis acid sites along with coke molecules from the reactants transformation. For n-heptane, the additional activity decay due to phenol is observed since the beginning of the reaction, while for methylcyclohexane it was only detected after few minutes. The increase of temperature disfavours phenol adsorption but, contrarily to methylcyclohexane, it does not prevent the phenol deactivating effect for n-heptane. Differences in the reactivity of n-heptane and methylcyclohexane molecules and IR spectroscopy data allow concluding that phenol firstly interacts with the stronger protonic sites, being then retained on the weaker acid sites. Alkylation of phenol is a reaction occurring in a lower extent under the conditions tested, being responsible for the consumption of light olefins. Finally, the adsorption of phenol favours the formation of branched molecules. Hence, the alkanes cracking should be more affected than the naphthenes cracking in the co-processing of conventional FCC feedstocks with hydrotreated bio-oils rich in phenolic compounds, being the deactivating effect certainly dependent on the quantity of bio-oils incorporated. © 2010 Elsevier B.V. All rights reserved.

1. Introduction The use of fossil fuels is the main cause of carbon dioxide emissions that are responsible for the greenhouse effect [1]. They are used in many important sectors, such as heat and power generation and the transportation sector. Therefore, it is imperative to find renewable energy sources able to replace the fossil fuels and, consequently, to avoid climatic changes. Nevertheless, if the heat and power sector can be supplied by different renewable sources, wind, solar, hydropower and biomass, the transportation sector has a more limited choice [2–4]. At this instance, biomass is the only renewable source of carbon that can be converted into liquid fuels to be used as transportation fuels [5]. Among some biomass sources (sugars, vegetable oils, etc.), lignocellulosic materials (residues from agriculture and forestry) are the most abundant and the only one that does not compete with the food [1,2,5]. To obtain a liquid product that could be used as feedstock in a wide range of refinery processes, lignocellulosic biomass must

∗ Corresponding author. Tel.: +351 21 841 9286; fax: +351 21 841 9198. E-mail address: [email protected] (J.M. Lopes). 0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.07.011

be transformed by fast pyrolysis or high-pressure liquefaction [5–7]. The bio-liquids produced, also named bio-oils, are a complex mixture of more than 400 different oxygenated hydrocarbons, as carboxylic acids, aldehydes, alcohols, ketones, esters, ethers, phenols, furans, carbohydrates and lignin-derived oligomers [8–12]. Depending on the technology employed, the quantity of oxygenated structures found in these oils can change. Typically, the oxygen content in pyrolysis oils can vary in the range 35–40 wt.%, whereas a liquefaction oil presents 16 wt.% of oxygen in its composition [5]. Hence, the amount of oxygenated compounds in the bio-oils is higher than that found in the petroleum derived-oils, ca. 1.0 wt.% [5], which contributes to a chemical composition significantly different from that of petroleum feedstocks. A good option for immediately producing bio-fuels could be to co-feed the bio-oils with the conventional Fluid Catalytic Cracking (FCC) feedstocks. Furthermore, this co-processing would be economically attractive because it uses a cheaper feedstock and an already existent refinery infrastructure. FCC is a mature technology that has revealed as a very versatile, flexible and robust process [13]. Actually, FCC modern units can receive a wide range of feedstocks and can adjust the operating conditions to maximize the production of gasoline, middle distillate (LCO) or light olefins

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to meet different market demands [14,15]. The typical FCC catalyst consists of a mixture of an inert matrix (kaolin), an active matrix (alumina), a binder (silica or silica-alumina) and Y-zeolite [15–18]. Nevertheless, this brings new challenges for the FCC units operation. Some authors [19–22] showed that the direct addition of the bio-oils to the FCC feedstocks is not so far feasible because of their minor miscibility with hydrocarbons, chemical instability and high tendency to form coke, being necessary a previous upgrading step. Thus, a hydrodeoxygenation treatment (HDO) of the bio-oils can be envisaged before the co-feeding, as it was proposed by Lappas et al. [21]. However, while carbonyl and carboxylic functions are easily converted into hydrocarbons at relatively low temperatures (200–300 ◦ C), the phenolic molecules are particularly refractory to HDO [23,24]. Furthermore, the presence of this type of compounds can also compromise the activation of the typical hydrotreating catalyst (CoMo or NiMo) because of the competitive adsorption effect established between phenols and H2 S (activating agent) [25–27]. So that, even after this treatment, phenols will be present in the bio-oils that would be introduced in the FCC units. Recently, to simulate the bio-oil/FCC feedstock co-feeding, we studied the effect of phenol addition on the methylcyclohexane transformation over HY zeolite [28]. It was proved that, at 350 ◦ C, the presence of phenol contributes to an additional zeolite deactivation, observed after 5 min of time-on-stream, which results from phenol adsorption on the zeolite acid sites along with methylcyclohexane coke molecules. This deactivation revealed to be only partial for all the contact times tested. Moreover, the increase of the reaction temperature to 450 ◦ C limits the phenol effect on the zeolite activity. A similar work was also performed at conditions close to that of FCC process (535 ◦ C, fixed-fluidized bed reactor) [29]. In this case, a mixture of gasoil and 10 wt.% of phenol was transformed over an FCC equilibrium catalyst. In fact, phenol demonstrated to have a low impact on the catalyst performance. However, under these conditions, phenol was transformed essentially into benzene, which can be critical to meet the gasoline specifications (benzene <1 vol.%). The goal of this paper is to compare the influence of phenol when processed along with different types of molecules representative of the FCC feedstocks (naphthenes and paraffins). Thus, the n-heptane transformation was carried out in the presence of phenol over an HY zeolite (the most important active phase of the FCC catalyst), at 350 and 450 ◦ C. The results will be compared with those previously obtained for methylcyclohexane [28]. The nheptane cracking has the particularity to be a more acid strength demanding reaction because of the nature of carbocations involved in the transition states. Actually, the initiation step for methylcyclohexane proceeds with the formation of a tertiary carbocation, whereas for n-heptane only a secondary one is formed, considering the preponderance of the classical ␤-scission mechanism [30]. Therefore, n-heptane cracking needs stronger acid sites than methylcyclohexane. This difference in the reactivity could provide good information to understand how phenol adsorption takes place on the zeolite and how the transformation of the different classes of compounds present in the feedstock is affected in the presence of this O-compound.

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2. Experimental 2.1. Zeolite characterization The HY zeolite, supplied by PQ (CBV500) as NH4 -USY, was obtained by calcination at 550 ◦ C under air flow. The physicochemical properties of the fresh zeolite are given in Table 1. The fresh sample was characterized by nitrogen adsorption and by FT-IR spectroscopy. The coked catalysts, besides the mentioned techniques, were also submitted to elemental analysis. Nitrogen adsorption measurements were carried out at −196 ◦ C on a Micrometrics ASAP 2010 apparatus. Before adsorption, the zeolite samples were degassed under vacuum at 90 ◦ C for 1 h and then at 350 ◦ C for 12 h (fresh samples) or at 150 ◦ C for 1 h (coked samples). The total pore volume (Vtotal ) was calculated from the adsorbed volume of nitrogen for a relative pressure P/P0 of 0.97, whereas the micropore volume (Vmicro ) and the external surface area (Sext ) were determined using the t-plot method [31,32]. The mesopore volume (Vmeso ) was given by the difference Vtotal − Vmicro . The zeolite acidity was measured by pyridine adsorption followed by IR spectroscopy on a Nicolet Nexus spectrometer. The samples were pressed into thin wafers (10–20 mg/cm2 ) and pretreated in an IR quartz cell under secondary vacuum (10−6 mbar) at 450 ◦ C for 3 h (fresh sample) and at 200 ◦ C for 1 h (coked samples). After the pre-treatment, the samples were cooled down to 150 ◦ C and contacted with pyridine vapour (Peq = 2–3 mbar) for 10 min. Then, pyridine excess was removed for 1 h under secondary vacuum and the IR spectra were recorded. The concentrations of Brönsted and Lewis sites able to retain the pyridine at 150 ◦ C were determined using the integrated areas of the bands at 1541 and 1454 cm−1 , respectively, and the extinction coefficients determined by Guisnet et al. [33]. The carbon content retained within the zeolites was analyzed by total combustion with a mixture flow of helium and oxygen in a Fisons Instruments EA 1108 CHNS-O. 2.2. Catalytic tests Before the reaction, the catalysts were pre-treated at 450 ◦ C under nitrogen flow (60 mL min−1 ) for 8 h. The catalytic tests were carried out in a pyrex fixed-bed reactor at 350 ◦ C or 450 ◦ C, under atmospheric pressure. The reactor feed was constituted by 10 mol% of n-heptane (Merck, 99%) and 90 mol% of N2 . In the poisoning tests, different quantities of phenol (Sigma–Aldrich, 99%) were injected with the n-heptane. The pure reactant and the mixture flow rates were maintained constants with a B.Braun compact perfusor. The nitrogen flux was controlled by a BROOKS Instrument. The reactor effluent samples were taken for different time-on-stream (TOS) values: 1.5, 3, 5, 10, 15, 30 and 60 min, using a 10-position valve supplied by VICI. The first TOS value was the time necessary to get a stable reactant pressure in the reactor. The tests were performed for contact times ( = 1/WHSV) that varied between 0.9 and 7 min. The contact time values were altered by changing the catalyst mass and maintaining the n-heptane flow constant (4 mL h−1 ). The reaction products were on-line analyzed by a SHIMADZU GC-14B gas chromatograph with a Plot Al2 O3 /KCl fused silica capillary column

Table 1 Physicochemical properties of the fresh HY sample. Si/Ala

2.9

Si/AlIV b

3.9

Crystallite size (␮m)

0.5

External surface (m2 g−1 )

32

Porosity (cm3 g−1 )

Acidity (␮mol g−1 )

Vmicro

Vmeso

Brönsted

Lewis

0.245

0.085

642

330

Note: Vmicro = micropore volume; Vmeso = mesopore volume. a Global Si/Al ratio determined from elemental analysis. b Framework Si/Al ratio calculated from the unit cell parameter (a0 = 2.453 nm), using the Breck–Flanigen equation [34].

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(50 m), using a flame ionization detector and nitrogen as carrier gas. To detect the presence of phenol and oxygenated products in the reactional medium, the reaction products were qualitatively analyzed by a Chrompack CP 9001 gas chromatograph with a CP Sil 5CB fused silica capillary column (50 m), using a flame ionization detector. 3. Results and discussion 3.1. Catalytic activity and deactivation Fig. 1a and b show the evolution of n-heptane conversion along with time-on-stream (TOS) for the catalytic tests performed with the pure n-heptane and the n-heptane/phenol mixtures (1.2 and 4.0 wt.% of phenol), at respectively 350 and 450 ◦ C, for a contact time of 4 min. In a previous work [28], the influence of phenol on the catalytic properties of the same HY zeolite was analyzed for another model reaction, the methylcyclohexane transformation, evaluating the changes induced by phenol in the activity, selectivity and stability of the zeolite. 3.1.1. Pure n-heptane transformation Comparing the pure n-heptane tests with those obtained for methylcyclohexane [28], it can be observed that n-heptane and methylcyclohexane transformations are very distinct reactions. In fact, whatever the reaction temperature, smaller conversion values are obtained for the n-heptane transformation for the same contact time, which demonstrates its difficulty to crack, as men-

Fig. 1. n-Heptane conversion vs. time-on-stream for a contact time  = 4 min during the transformation of pure n-heptane (), n-heptane + 1.2 wt.% phenol (♦) and nheptane + 4.0 wt.% phenol (), at 350 ◦ C (a) and 450 ◦ C (b).

Fig. 2. Carbon content vs. time-on-stream for a contact time  = 4 min, during the transformation of pure n-heptane (closed symbols) and n-heptane + 4.0 wt.% phenol (open symbols), at 350 ◦ C () and 450 ◦ C ().

tioned before. In general, the n-heptane transformation is three times slower at 350 ◦ C and two times at 450 ◦ C. Furthermore, for n-heptane, the activity decay is stronger and faster than for methylcyclohexane, and, after 10 min TOS, the deactivation does not stop, like in the case of methylcyclohexane, but slightly proceeds to very low conversions. As well as for methylcyclohexane, this decrease in the n-heptane conversion is accompanied by an increase in the amount of the bulky aromatic compounds (coke) deposited on the zeolite pores, which mainly occurs in the first 10 min of TOS, as it can be seen in Fig. 2. After this period, there is a stabilization of the carbonaceous materials accumulation, as expected by the n-heptane conversion profile. Comparing the nheptane (Fig. 1a and b) and methylcyclohexane conversion curves [28], one could think that the carbon content trapped on the zeolite during n-heptane transformation would be higher. However, if we compare the amount of carbon retained inside the zeolite pores after 60 min TOS for n-heptane (5.4 and 7.4 wt.%, at 350 and 450 ◦ C) and methylcyclohexane (5.7 and 7.2 wt.%, at 350 and 450 ◦ C), it can be concluded that there is no more carbon accumulation for n-heptane. So, this reveals that the n-heptane cracking is more sensible to the presence of coke molecules, i.e. the same amount of coke during n-heptane transformation causes a greater deactivation of the zeolite. Actually, both n-heptane cracking and coke formation reactions seem to compete for the same acid sites, the stronger ones. Moreover, as well as for methylcyclohexane [28], the toxicity of the coke produced during n-heptane transformation also varies with the reaction temperature. At higher temperatures, despite the amount of coke in the catalyst is higher, the stability of the zeolite increases, i.e. the deactivation is not so abrupt (Fig. 1a and b). In fact, the coke formed at lower temperatures is more toxic, as it is shown in Fig. 3: for the same amount of carbon, the n-heptane residual activities are always lower at 350 ◦ C. A similar behaviour was also previously reported by other authors [35–37]. 3.1.2. Phenol influence 3.1.2.1. n-Heptane transformation. The presence of phenol in the reactant feed leads to an additional deactivation of the zeolite that is very dependent on the reaction temperature (Fig. 1a and b). In addition, whatever the temperature, the activity loss of the catalyst due to phenol is observed since the beginning of the reaction (1.5 min TOS). Hence, while at 350 ◦ C the quantity of phenol injected plays an important role in the catalyst deactivation, at 450 ◦ C different amounts of phenol have identical effects. In fact, at 350 ◦ C,

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Fig. 3. Pure n-heptane residual conversions (defined as the ratio between the conversions at t min and 1.5 min TOS) as a function of carbon content, at 350 ◦ C () and 450 ◦ C (), for a contact time  = 4 min.

with 1.2 wt.% of phenol added, no additional deactivating effect is observed. The catalyst deactivation only becomes more important in the presence of higher quantities of phenol, e.g. 4.0 wt.% of phenol. However, when the temperature increases to 450 ◦ C, 1.2 wt.% of phenol has already a negative influence on the catalyst activity, but, in this case, the increase of the phenol addition to 4.0 wt.% does not contribute to an enhancement of the zeolite deactivation. This may suggest that at 450 ◦ C, with 1.2 wt.% of phenol injected, a maximum in the phenol deactivating effect was already achieved. Fig. 2 illustrates the evolution of the carbon content as a function of the TOS in the absence or presence of phenol (4.0 wt.% of phenol), at 350 and 450 ◦ C, for a contact time of 4 min. As expected, the more pronounced deactivation of the catalyst in the presence of phenol is related to a significant increase of the carbonaceous materials deposited inside the zeolite pores that happens since 1.5 min TOS. Furthermore, it can be noticed in Fig. 4a and b that, while at 450 ◦ C the evolution of n-heptane conversion as a function of carbon content for the pure n-heptane and n-heptane/4.0 wt.% phenol mixture is similar, at 350 ◦ C the toxicity of the carbon deposits seems to decrease when phenol is fed with n-heptane. This could explain the fact that, at 350 ◦ C, no differences were found between the pure n-heptane and n-heptane/1.2 wt.% phenol mixture conversion curves (Fig. 1a), although the amount of carbon deposited on the zeolite, after 60 min of TOS, in the presence of 1.2 wt.% of phenol (9.9 wt.%) is much higher than for pure n-heptane (5.4 wt.%). On the other hand, as the increase of the quantity of phenol injected from 1.2 wt.% to 4.0 wt.% contributes to an enhancement of the phenol deactivation level, the impact of this oxygenated compound on the n-heptane conversion becomes detectable. Considering that the additional carbon content obtained in the presence of phenol is only due to phenol adsorption on the acid sites, as previously noticed [28] from analysis of coked samples performed by infrared spectroscopy and soluble coke extraction followed by GC–MS, the whole difference between the amounts of carbon deposited on the catalyst with and without phenol could give information about the phenol quantity that remains accumulated on the zeolite. The comparison between these values and the amount of phenol injected at each TOS, for a mixture of 4.0 wt.% phenol, is presented in Table 2, for both temperatures. As it can be seen, the quantity of phenol injected is always significantly higher than the amount of phenol trapped on the zeolite pores, even for 1.5 min TOS. As a result, the phenol adsorption seems to be limited since the first minutes of the reaction. Moreover, the rate of phenol accumulation reduces with the increase of the TOS.

Fig. 4. Evolution of n-heptane conversion as a function of carbon content for the tests performed with pure n-heptane () and n-heptane + 4.0 wt.% phenol (), at 350 ◦ C (a) and 450 ◦ C (b), for a contact time  = 4 min.

Evaluating the quantity of phenol accumulated at both temperatures, it can be noticed that the higher the temperature, the lower the phenol deposition, except for a TOS of 60 min. Therefore, it can be concluded that at higher temperatures there is a slight decrease of the phenol adsorption. All this phenomena can be confirmed by the representation of the n-heptane residual activities along TOS in the presence of phenol, at 350 and 450 ◦ C (Fig. 5). Effectively, at 450 ◦ C, between 5 and 30 min TOS a more limited zeolite deactivation is registered. Nevertheless, with the increase of the TOS, this beneficial effect of the temperature is reduced. Perhaps, for longer TOS, the amount of carbon deposited on the zeolite is so high that it could start to hinder the phenol desorption of the zeolite acid sites. For 1.5 min TOS, even if the quantity of phenol accumulated Table 2 Amounts of phenol deposited on the zeolite at 350 and 450 ◦ C (contact time  = 4 min) estimated from the nitrogen adsorption measurements and from the carbon contents and phenol injected for a mixture of 4.0 wt.%, for each time-on-stream (TOS). TOS (min)

1.5 5 10 30 60

Accumulated phenol (mmol g−1 ) Carbon content

Nitrogen adsorption

350 ◦ C

450 ◦ C

350 ◦ C

450 ◦ C

0.097 0.469 0.519 0.719 0.785

0.068 0.247 0.490 0.644 0.917

0.095 0.443 0.578 0.802 0.836

0.063 – 0.440 0.758 1.43

Injected phenol (mmol g−1 )

0.188 0.627 1.25 3.76 7.53

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I. Grac¸a et al. / Applied Catalysis A: General 385 (2010) 178–189 Table 3 Product distribution obtained during the n-heptane transformation in the absence and presence of phenol over the fresh sample (1.5 min TOS), at 350 ◦ C.

Fig. 5. Catalyst residual activity for the n-heptane/4.0 wt.% phenol mixture (nheptane conversion measured after t min for the mixture n-heptane + 4.0 wt.% phenol and the pure n-heptane conversion measured after 1.5 min of reaction) vs. time-on-stream at 350 ◦ C () and 450 ◦ C (), for a contact time  = 4 min.

at 450 ◦ C is lower, an identical decrease of the n-heptane conversion (about 25%) is achieved at both temperatures. Thus, it can be concluded that only 0.07 mmol g−1 is sufficient to strongly deactivate the zeolite, whereas 0.2 mmol is injected (4.0 wt.% of phenol). This signifies that at higher temperatures the number of protonic sites able to adsorb the phenol molecules seems to be inferior. This can be probably due to the exothermic nature of the adsorption process. As known, the increase of the temperature is responsible for a decrease of the adsorption equilibrium constant associated to the different acid sites. However, for the initial reaction times, the phenol effect on the n-heptane conversion at 450 ◦ C continues to be as high as at 350 ◦ C. Perhaps that, in the beginning of the reaction, as the quantity of phenol injected per gram of zeolite is still low, phenol preferentially interacts with the stronger protonic sites, which are also responsible for the n-heptane conversion. Therefore, if the adsorption equilibrium of these protonic sites would not be so affected by the temperature, they are still able to adsorb the phenol at 450 ◦ C. Hence, the same decrease of the zeolite activity would be expected at both temperatures. For higher TOS comprised in the range 5–30 min, as the stronger acid sites are already occupied, phenol starts to be adsorbed on the weaker ones, and, so, the positive influence of the higher temperature on the nheptane conversion begins to be visible. The interaction of phenol with the Brönsted acid sites will be further analyzed during the discussion of the IR spectroscopy results. Indeed, phenol started to be detected on the reaction products after 9 min of TOS, in quantities that increased with the TOS. It was also observed that the quantity of phenol present on the effluent is always higher at 450 ◦ C than at 350 ◦ C. Moreover, the difference between the amounts of phenol found on the effluent at 350 and 450 ◦ C seems to reduce with the TOS.

3.1.2.2. n-Heptane vs. methylcyclohexane. For methylcyclohexane, at 350 ◦ C a more pronounced additional deactivation was noticed in the presence of 1.2 wt.% of phenol [28], but the carbon content found on the zeolites after 60 min TOS was similar for both n-heptane (9.9 wt.%) and methylcyclohexane transformations (9.0 wt.%). This can be explained by the toxicity of the carbonaceous materials deposited on the zeolite during methylcyclohexane transformation that revealed to be identical in the presence or absence of phenol [28], contrarily to what happens for n-heptane. Therefore, this become more visible the phenol influence on the methylcyclohexane conversion.

Pure n-Hp

n-Hp + 1.2 wt.% phenol

n-Hp + 4.0 wt.% phenol

Selectivity (wt.%) Methane Ethane Ethylene Propane Propylene Butanes Butenes Pentanes Pentenes Hexanes Hexenes Heptenes n-Heptane isomers Toluene Xylenes

0.01 0.03 0.28 26.3 6.3 49.2 2.2 7.7 0.3 3.5 0.08 0.04 1.0 0.6 1.8

0.01 0.03 0.26 26.7 5.8 51.1 2.1 7.5 0.3 3.5 0.03 0.05 0.8 0.6 1.2

0.01 0.04 0.26 26.9 4.2 52.5 1.4 7.5 0.2 3.3 0.06 0.05 1.0 0.8 1.7

Conversion (%) Contact time (min)

20.5 4

20.3 4

27.1 5

8.1 7.3

8.9 7.7

12.5 8.1

Molar ratios Paraffins/olefins (iC4 + iC5 )/(nC4 + nC5 ) paraffins

An important remark is that, for methylcyclohexane, the effect of phenol was not detected initially but only after 5 min TOS [28], whereas for n-heptane its influence was detectable since the beginning of the reaction (after 1.5 min TOS). Whereas n-heptane needs strong acid sites to isomerise and crack, methylcyclohexane transformation can also be promoted by less strong acid sites. So if for lower TOS values, phenol molecules preferentially interact with the stronger protonic sites, an important induced decrease of the n-heptane conversion would be expected even at the first TOS value. Contrarily, for the methylcyclohexane, the additional catalyst deactivation revealed truly important when phenol deposition on the weaker acid sites starts, i.e. after the first 5 min TOS. This could explain the behaviour reported at higher temperatures for methylcyclohexane: the higher the temperature, the lower the deactivation observed for higher TOS. Actually, the adsorption ability of the weaker protonic sites is reduced at 450 ◦ C. As a result, while for methylcyclohexane the increase of temperature partially prevent the additional deactivation due to phenol, for n-heptane the deactivating effect of this O-compound is so important at 350 ◦ C, as well as at 450 ◦ C. Furthermore, for both reactant molecules, although the important increase of the carbon content deposited on the zeolites in the presence of phenol, the poison addition does not seem to extremely affect the n-heptane and methylcyclohexane initial conversions. This is in agreement with the low impact of phenol on the performances of the FCC equilibrium catalyst recently reported in a related study carried out under FCC operating conditions [29]. This suggests that the conditions of the present work could give valuable information on the effect of phenol presence in the FCC feedstock. 3.2. Products distribution 3.2.1. Pure n-heptane transformation Tables 3 and 4 present the products distribution obtained after 1.5 min TOS, at similar conversion levels, during the n-heptane transformation at respectively 350 and 450 ◦ C, in the absence and presence of phenol. The high relative amounts of C3 and C4 species (84% at 350 ◦ C and 86% at 450 ◦ C) among the transformation products clearly indicate the preponderance of the classical ␤-scission mechanism for pure n-heptane cracking at both temperatures, as

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Table 4 Product distribution obtained during the n-heptane transformation in the absence and presence of phenol over the fresh sample (1.5 min TOS), at 450 ◦ C. Pure n-Hp

n-Hp + 1.2 wt.% phenol

n-Hp + 4.0 wt.% phenol

Selectivity (wt.%) Methane Ethane Ethylene Propane Propylene Butanes Butenes Pentanes Pentenes Hexanes Hexenes Heptenes n-Heptane isomers Toluene Xylenes

0.1 0.3 0.9 24.3 15.1 38.3 8.3 4.9 1.1 1.3 0.3 1.3 0.0 1.3 2.4

0.1 0.2 0.8 26.2 9.7 45.4 4.7 5.8 0.7 1.5 0.3 0.1 0.0 1.3 2.2

0.1 0.3 1.1 27.3 10.4 45.8 4.8 5.1 0.6 1.1 0.1 0.3 0.0 1.6 1.3

Conversion (%) Contact time (min)

30.8 2

37.8 4

38.6 4

2.5 3.4

4.4 4.5

4.1 4.4

Molar ratios Paraffins/olefins (iC4 + iC5 )/(nC4 + nC5 ) paraffins

previously reported [38–40]. According to the n-heptane cracking ␤-scission mechanism, an isomerisation step precedes the cracking step. To a lesser extent, also methane, C2 , C5 , C6 can be found on the effluent formed through protolytic cracking and/or olefins transformation (oligomerisation followed by cracking). Whatever the reaction temperature, cracking products are mainly paraffins. In fact, the paraffins/olefins ratio obtained at 1.5 min TOS for different contact times (0.9–7 min at 350 ◦ C and 0.9–4 min at 450 ◦ C) varies from 3 to 14 at 350 ◦ C and from 2 to 4 at 450 ◦ C, for conversions rising from 5.5 to 42% at 350 ◦ C and from 23 to 53% at 450 ◦ C. The detected aromatics, leaving the porous network, are mainly toluene and xylenes, always observed in low amounts. Therefore, generally, the reaction products can be divided in three different groups: cracking products (olefins and paraffins), n-heptane isomers and aromatics. Figs. 6 and 7 represent the evolution of the cracking products, n-heptane isomers and aromatics yields obtained during the transformation of pure n-heptane over the fresh (1.5 min TOS) and coked zeolites (obtained between 15 and 60 min TOS), for different contact times (0.9–7 min at 350 ◦ C and 0.9–4 min at 450 ◦ C), at respectively 350 and 450 ◦ C. Observing Figs. 6a and 7a, it is possible to see that, for higher TOS, there is a small decrease of the cracking products selectivity. This is probably due to the preferential poisoning of the stronger sites by coke molecules, in which cracking reactions take place. Consequently, a slight increase of the isomers yield was also observed. An identical tendency was already verified for the coked samples obtained during methylcyclohexane transformation [28]. Concerning the aromatic evolution along TOS, an increase of the aromatics amount on the effluent was also noticed for longer TOS values (Figs. 6b and 7b). As observed in Fig. 2, the rate of coke formation is very high in the first minutes of reaction, but its production slows down for longer TOS. This means a decrease of the amount of aromatic molecules that participate in the coke formation reactions with the TOS, which explains the increase of the aromatic selectivity for the coked zeolites. Furthermore, there is also a decrease of the paraffins/olefins ratio with the increase of the zeolite deactivation. Actually, after 60 min TOS, paraffins/olefins ratios of about 1.4–2.3 at 350 ◦ C and 1–1.5 at 450 ◦ C were observed, with the increase of the contact

Fig. 6. (a) Cracking products () and n-heptane isomers (♦) yields; (b) aromatics yields () vs. n-heptane conversions obtained for contact times rising from 0.9 to 7 min, at 350 ◦ C. Fresh zeolite (1.5 min TOS, closed symbols) and deactivated zeolite (TOS comprised between 15 and 60 min, open symbols).

time (0.9–7 min at 350 ◦ C and 0.9–4 min at 450 ◦ C). This is not surprising considering that the importance of hydrogen transfer secondary reactions decreases with the coke deposition along TOS [41,42]. 3.2.2. Phenol influence 3.2.2.1. n-Heptane transformation. Shorter TOS value (1.5 min). The effect of phenol on the selectivity of the products families (cracking products, n-heptane isomers and aromatics) was also investigated. At both temperatures, it was observed an additional increase of the zeolite deactivation in the presence of phenol since the beginning of the reaction. However, apparently, the selectivities of the products families after 1.5 min TOS do not change. However, whatever the temperature, the paraffins/olefins ratio increases in the presence of phenol (Tables 3 and 4). This means that less unsaturated species are present on the reactor effluent when phenol is added in the feed. Actually, a decrease of the C3 and C4 olefins was identified in the presence of phenol, whereas the selectivity for the other cracking products remained practically the same. Therefore, phenol alkylation could be a reaction that takes place. Furthermore, the tests carried out with a chromatographic column able to detect oxygenated compounds showed that, along with phenol, phenolic structures with higher molecular weights can also be found but in minor amounts. A similar behaviour for phenol transformation was already reported by other authors [29,43]. The (iC4 + iC5 )/(nC4 + nC5 ) paraffins ratios were also calculated at iso-conversion, for the tests performed with pure n-heptane and n-

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Fig. 7. (a) Cracking products () and n-heptane isomers (♦) yields; (b) aromatics yields () vs. n-heptane conversion obtained for contact times rising from 0.9 to 4 min, at 450 ◦ C. Fresh zeolite (1.5 min TOS, closed symbols) and deactivated zeolite (TOS comprised between 15 and 60 min, open symbols).

heptane + phenol, at 350 and 450 ◦ C (Tables 3 and 4). In both cases, there is an increase of this parameter when phenol is fed with the reactant. As known, the existence of branched C4 and C5 paraffins results from the n-heptane isomerisation prior to the scission reaction. Nevertheless, highly substituted aromatics and polyaromatics with various rings can be already found after 1.5 min of TOS [44–47]. Consequently, the adsorption of this type of molecules could reduce the space for the n-heptane highly branched isomers formation and diffusion (steric constraints). Possibly, the change in the nature of the carbonaceous materials deposited on the zeolite due to phenol adsorption should slightly overcome this spatial limitation. Actually, the adsorption of phenol molecules instead of polyaromatics in surrounding acid sites would create a high open space between coke molecules. With the increase of the temperature to 450 ◦ C, this difference in the (iC4 + iC5 )/(nC4 + nC5 ) paraffins ratio becomes more evident because more condensed aromatic species are formed at this temperature [44,45]. Hence, the substitution of a >4 ring molecule to a 1 ring compound (phenol) seems to be very beneficial to the formation of branched compounds. Longer TOS values (15–60 min). For longer TOS, comprised between 15 and 60 min, for which the zeolite deactivation is higher, at 350 ◦ C, there is a small decrease of the cracking products selectivity and, consequently, an increase of the isomers selectivity, in the presence of phenol (Fig. 8a), which depend on the quantity of poison added. At 450 ◦ C (Fig. 8b), the cracking products selectivity is similar without and with phenol. On the other hand, no differences

Fig. 8. Cracking products () and n-heptane isomers (♦) yields vs. n-heptane conversion for the pure n-heptane (black symbols), n-heptane + 1.2 wt.% phenol (grey symbols) and n-heptane + 4.0 wt.% phenol (open symbols), at 350 ◦ C (a) and 450 ◦ C (b), for deactivated zeolite (all values between 15 and 60 min TOS for the different contact times studied).

were observed in the aromatics selectivity for the tests performed with phenol during n-heptane transformation, which signifies that, the aromatic consumption in the coke formation reactions is not altered by the poison. 3.2.2.2. n-Heptane vs. methylcyclohexane. For both n-heptane and methylcyclohexane transformations at 350 ◦ C, the results obtained for the first experimental value (1.5 min TOS for n-heptane and 2 min TOS for methylcyclohexane) did not evidence an effect of phenol addition on the selectivity for cracking products, n-heptane isomers and aromatics. After 2 min TOS, the paraffins/olefins ratio obtained, at iso-conversion (30%), during the transformation of pure methylcyclohexane and methylcyclohexane + 1.2 wt.% phenol at 350 ◦ C were, respectively, 12.1 and 12.3, which signifies that this ratio is not altered in the presence of phenol. Therefore, it can be said that the hydrogen transfer reactions are not affected by phenol. Furthermore, observing in more detail the product distribution for the methylcyclohexane transformation, it was also possible to see a slight decrease of the C4 olefins in the presence of phenol after 2 min of TOS (selectivity: 0.14–0.24% for pure methylcyclohexane and 0.08–0.10% with phenol), as in the case of n-heptane, which confirms the hypothesis of phenol alkylation. As a result, an increase of the paraffins/olefins ratio should be expected, as previously observed for n-heptane. However, as for the methylcyclohexane transformation the olefin content of the effluent is lower, due to the greater importance of the hydrogen transfer reactions, the impact of the C4 olefins yield reduction on this ratio is not as

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visible as for the n-heptane. Concerning the (iC4 + iC5 )/(nC4 + nC5 ) paraffins ratio observed for methylcyclohexane reaction at 350 ◦ C, after 2 min of reaction at iso-conversion (30%), no significant modifications were found between the values determined for the tests performed in the absence (10.6) and presence of phenol (9.8). This result does not agree with what was observed during n-heptane reaction (Table 3). The differences on the behaviour observed for methylcyclohexane and n-heptane could be related to the spatial configuration of these two reactants and their isomers. The linearity of the n-heptane isomers contrasts with the more rigid structure of the methylcyclohexane isomers. Therefore, even if phenol adsorption allows favouring the more branched molecules formation and diffusion, in the case of methylcyclohexane transformation this does not happen because methylcyclohexane isomers are bulkier and less flexible than n-heptane isomers. Due to the major differences between the conversion values achieved during the transformation of both reactants for longer TOS, the comparison between the products distributions obtained for n-heptane and methylcyclohexane in the presence of phenol was not studied. 3.3. Role of phenol on zeolite deactivation 3.3.1. Coke characterization by IR spectroscopy The nature of the carbonaceous materials formed and deposited on the zeolite during the n-heptane transformation without and with 4.0 wt.% of phenol (contact time of 4 min) was analyzed by infrared (IR) spectroscopy, for different TOS and temperatures (Figs. 9 and 10). For the tests carried out with pure n-heptane (Fig. 9), the presence of bands in the regions 1700–1500 cm−1 (aromatic C–C stretching vibration region) and 1450–1300 cm−1 (C–H bending vibration region) indicates the existence of methyl polyaromatic compounds [48]. Comparing the pure n-heptane coke spectra recorded for a TOS of 60 min at 350 ◦ C (Fig. 9a) with those obtained during the pure methylcyclohexane transformation over the same zeolite sample [28], it is clear that, for the same carbon content (5.4 wt.% for nheptane and 5.7 wt.% for methylcyclohexane), the nature of the coke is similar. Therefore, it can be said that the same species are present in coke produced from n-heptane cracking, as methylnaphthalenes, methylanthracenes, methylphenanthrenes, methylbiphenyls, methylpyrenes and methylchrysenes. The increase of the temperature influences the nature of the coke formed, as can be observed in Fig. 9b. In fact, at 450 ◦ C, the more intense aromatic C–C band appears at 1608 cm−1 , whereas at 350 ◦ C the higher absorbance corresponds to the band at 1590 cm−1 , which could suggest the presence of condensed polyaromatics with higher molecular weights at 450 ◦ C. According to Eberly et al. [49], the higher the intensity of the band at 3050 cm−1 (stretching vibrations of C–H unsaturated species), the higher the aromaticity of the coke. Actually, at 450 ◦ C, the area of the 3050 cm−1 band is higher than at 350 ◦ C. The increase of the TOS is accompanied by an increase of the intensity of the coke bands, which is in agreement with the increase of the carbon content trapped on the zeolite pores (Fig. 2). Generally, the integrated area of the 1600 cm−1 band is proportional to the amount of coke deposited [40,48]. Moreover, it is possible to see a displacement C–C coke bands to higher frequencies, which expresses the increase of the aromaticity of the coke molecules with the TOS [48]. In the spectra recorded for the coked samples obtained in the presence of phenol at 350 and 450 ◦ C (Fig. 10), along with the methylpolyaromatic bands already described new bands appear at 1490 and 1509 cm−1 . A significant increase of the band at ca. 1600 cm−1 can be also observed for the tests carried out with phenol, which can be related to the appearance of a band at 1595 cm−1 . Similar bands were already observed for the methylcyclohexane

Fig. 9. 1300–1700 cm−1 region of the FT-IR spectra of the HY zeolite coked during pure n-heptane transformation for a contact time  = 4 min, at 350 ◦ C (a) and 450 ◦ C (b).

transformation over an HY zeolite in the presence of 1.2 wt.% of phenol [28] and, according to the literature [50–52], they were attributed to adsorbed phenol molecules. The areas of these bands increase with TOS, showing an increase in the amount of phenol adsorbed on the zeolite.

3.3.2. Effect of deactivation on the zeolite porosity Fig. 11 shows the evolution of the micropore and mesopore volumes, determined by nitrogen adsorption at −196 ◦ C, as a function of TOS, for the catalytic tests carried out with pure n-heptane and with n-heptane/4.0 wt.% phenol mixture ( = 4 min), at 350 and 450 ◦ C. For the pure n-heptane transformation, besides the abrupt decrease of the n-heptane conversion with the increase of TOS, only a slight reduction of the micropore volume is observed, at both temperatures. This confirms that only a limited number of acid sites (the stronger ones) are able to convert the n-heptane molecules, as it was previously mentioned in this article. The addition of phenol in the feed is responsible for a more pronounced reduction of the micropore volume, in agreement with the additional increase of the amount of carbonaceous materials deposited on the zeolite in the presence of the poison. On the other hand, no significant changes were noticed in terms of the mesopore volume, when phenol is added. Similar results were reported in Ref. [28], for the methylcyclohexane transformation in the presence of phenol, over the same HY zeolite.

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Fig. 11. Evolution of the micropores () and mesopores () volumes as a function of time-on-stream in the absence (closed symbols) and presence of phenol (open symbols), for a contact time of 4 min, at 350 ◦ C (a) and 450 ◦ C (b).

Fig. 10. 1300–1700 cm−1 region of the FT-IR spectra of the HY zeolite coked during n-heptane + 4.0 wt.% phenol transformation for a contact time  = 4 min, at 350 ◦ C (a) and 450 ◦ C (b).

Based on the nitrogen adsorption experiments, it was possible to determine the amounts of phenol responsible for the additional decrease observed in the micropores volume. The values were determined by the difference between the micropore volumes obtained with and without phenol, assuming that this difference only corresponds to phenol molecules retained on the zeolite and taking the density of the liquid phenol at room temperature. The results obtained at both temperatures are presented in Table 2, where they are compared with those formerly estimated by the difference between the carbon contents in the absence and presence of phenol. As it can be seen, at 350 ◦ C, the values are quite similar for all TOS values, which could indicate that the increase of zeolite deactivation in the presence of phenol is due to the direct poisoning of the acid sites by phenol molecules, as in the case of the methylcyclohexane transformation at 350 ◦ C [28]. Actually, if the data from the adsorption were significantly higher than those from the carbon deposition, then some micropore volume should became inaccessible to nitrogen by blocking effect: a higher micropore volume reduction than that corresponding to the volume of phenol retained would be registered. At 450 ◦ C, an identical observation can be made, but only for the first minutes of reaction. In fact, for longer TOS, the values determined by the nitrogen adsorption

become higher than those calculated from the carbon content. Thus it seems that, at 450 ◦ C and for longer TOS, the deactivation induced by the phenol molecules is also due to pore blocking. Actually, at this temperature, 14 wt.% of carbon was deposited on the zeolite after 60 min TOS, which results, according to the IR spectroscopy, from the adsorption of the high molecular weight polyaromatic molecules and high amounts of phenol. 3.3.3. Effect of deactivation on the acidity The zeolite samples obtained at different TOS during pure nheptane and n-heptane/4 wt.% phenol transformations were also analyzed by pyridine adsorption followed by IR spectroscopy, in order to study the phenol influence on the zeolite acidity. The spectra obtained by the difference of the spectra recorded after and before pyridine adsorption showed, as it is usual, some characteristic bands of pyridine adsorbed on Brönsted and Lewis acid sites in the 1300–1700 cm−1 region, corresponding to pyridinium ions (1488, 1541 and 1631 cm−1 ) and pyridine coordinated to Lewis acid sites (1454, 1488 and 1620 cm−1 ). The intensity of the bands at 1541 and 1454 cm−1 allowed determining the concentration of both Brönsted and Lewis acid sites present on the zeolite samples. The results are presented in Fig. 12a and b, in which the evolution of the Brönsted and Lewis acid site concentrations, in the absence and presence of phenol, are plotted as a function of the time-on-stream, at 350 and 450 ◦ C, respectively. However, it is necessary to take into account that part of the coke and phenol molecules were displaced by the more basic pyridine molecules, resulting in the appearance of large negative bands at ca. 1360 and

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Fig. 12. Evolution of the number of Brönsted () and Lewis () acid sites along with time-on-stream for the pure n-heptane (closed symbols) and n-heptane + 4.0 wt.% phenol transformations (open symbols), at 350 ◦ C (a) and 450 ◦ C (b).

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1600 cm−1 (already evidenced in the spectrum reported in [28] for methylcyclohexane), and thus in an overestimation of the amount of acid sites determined. The same observation was already made by other authors [46,53]. For the zeolite samples coked at different TOS with pure n-heptane, at both temperatures, it is possible to see a decrease of the Brönsted acid sites concentration with the increase of TOS. Concerning the Lewis acidity, it remains practically constant. At higher temperatures, besides the higher quantity of carbon accumulated (see Fig. 2), the decrease of the protonic acidity with the TOS is inferior. Indeed, after 60 min of TOS, while at 350 ◦ C there is a reduction of the Brönsted site concentration of about 45% relatively to the fresh catalyst, at 450 ◦ C a loss of about 33% is attained. This is in agreement with the lower toxicity observed at higher temperatures. In the presence of phenol, the decrease of the protonic sites concentration is more pronounced. However, in this case, there is also a reduction of the Lewis acidity. In addition, the areas of the negative bands increase when phenol is added (spectra not shown), which means that the “real” decrease in the Brönsted sites concentration should be significantly higher than the reported values. Therefore, phenol adsorption takes place on both Brönsted and Lewis acid sites, contrarily to coke molecules produced from the reactant (n-heptane). Identical results were also obtained for methylcyclohexane [28]. Furthermore, for 1.5 min of TOS, phenol seems to be preferentially adsorbed on the Brönsted acid sites. In fact, for this TOS, the number of Lewis acid sites remains identical to that observed for the fresh catalyst, 330 ␮mol g−1 . Fig. 13a presents the difference between the spectra recorded before and after pyridine adsorption in the 3700–3400 cm−1 region, for the fresh and coked samples at different TOS, in the absence and presence of phenol, for a contact time of 4 min, at 350 ◦ C. These spectra show the Brönsted acid sites in interaction with the pyridine molecules at 150 ◦ C, i.e. the acidic and accessible protonic sites. Spectrum corresponding to the fresh sample shows the characteristic –OH bands present for a dealuminated HY zeolite: 3525, 3550, 3600, 3625, and 3665 cm−1 [46,53–55]. The bands at 3550 and 3625 cm−1 correspond to bridging hydroxyl located in the sodalite cages and in the supercages, respectively. On the other hand, the 3525 and 3600 cm−1 bands have been assigned to the same type

Fig. 13. (a) Difference between the spectra recorded before and after pyridine adsorption and (b) spectra recorded before pyridine adsorption, in the 3700–3400 cm−1 region, for the fresh and coked samples at different TOS (a: 1.5, b: 10, c: 30 and d: 60 min) during pure n-heptane (n-Hp) and n-heptane + 4.0 wt.% phenol transformation, for a contact time of 4 min, at 350 ◦ C.

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of hydroxyl in interaction with extra-framework Al (EFAL) species. The origin of the band at 3665 cm−1 is not very clear, possibly it corresponds to partial framework (OH)Al–O–Si groups existing in defects produced during steaming treatment [56], presenting an acid strength between that of traditional Al–OH–Si groups and that of hydroxyl groups linked to EFAL species [53]. Comparing the spectra in the 3400–3700 cm−1 (Fig. 13a) for the fresh catalyst and the pure n-heptane coked samples for different TOS, it is possible to observe a fast disappearance of the 3600 cm−1 band, corresponding to the strongest Brönsted acid sites [46,53]. A slight reduction of the bands at 3625 and 3665 cm−1 is also detected, being more important for the highest TOS values, principally after 30 min. These bands are attributed to weak and medium acidity hydroxyls, respectively [53]. Furthermore, there is also a small reduction of the band at 3525 cm−1 , mainly for longer TOS values. This is unexpected because this band corresponds to the Al–OH–Si groups in interaction with the EFAL species located in the sodalite cages, where normally no coke molecules can be formed [53]. Nevertheless, it is necessary to take into account that the spectra give information on the acid sites that can interact with pyridine molecules. For longer TOS, the carbon content trapped in the supercages should probably hinder the access to the pyridine molecules to this type of acid sites. In the presence of phenol, there is also a strong decrease of the band at 3600 cm−1 . Moreover, while at 1.5 min TOS the intensities of the bands at 3625 and 3665 cm−1 remain similar in the absence or presence of phenol (suggesting that the carbon contents of the zeolite are similar), a more important reduction of the areas of these bands can be observed in the presence of phenol after 10 min TOS, i.e. with the increase of the carbon content trapped on the zeolite due to phenol deposition. It can be also noticed a more significant decrease of the band at 3525 cm−1 when phenol is present, which should be related to the additional increase of the carbon content in the presence of phenol that reduces the pyridine access to this acid sites more than in the case of the pure n-heptane. These conclusions can be sustained by the observation of Fig. 13b, in which it is presented the hydroxyls region of the IR spectra recorded before pyridine adsorption. In this figure, it is also possible to observe that in the presence of phenol the reduction of the band at 3600 cm−1 (strongest protonic sites) is slightly higher than for the pure nheptane, even after 1.5 min TOS. The results obtained at 450 ◦ C are not presented because they are similar to that observed at 350 ◦ C. Hence, the observation of a more significant additional decrease of the medium and weaker acid sites due to the presence of phenol after 10 min TOS leads to the conclusion that, for the first TOS values, phenol should be retained on the stronger acid sites.

4. Conclusion The n-heptane transformation was carried out in the presence of phenol over an HY zeolite, at 350 and 450 ◦ C, and the results were compared with those previously obtained in a similar study with methylcyclohexane. For both reactants, the addition of phenol induces an additional deactivation of the zeolite due to phenol adsorption on Brönsted and Lewis acid sites along with polyaromatic coke molecules formed from the reactants transformation. Nevertheless, comparing the n-heptane and methylcyclohexane transformations, clear differences were observed concerning the HY catalytic behaviour in the presence of phenol. For n-heptane, an important decrease of the zeolite activity due to phenol is observed since the beginning of the reaction, while for methylcyclohexane the deactivating effect of phenol was only detected after 5 min TOS. Furthermore, contrarily to methylcyclohexane, for the n-heptane transformation the increase of the reaction temperature does not prevent the additional deactivation imposed by the presence of phenol, although the

lower phenol adsorption noticed at 450 ◦ C. Differences in the reactivity of n-heptane and methylcyclohexane molecules also allow concluding that phenol firstly interacts with the stronger protonic sites, being after that phenol retained on the weaker acid sites. The former conclusion was supported by the analysis of detailed IR spectroscopy characterization of the deactivated zeolites at different TOS values. Alkylation of phenol is a reaction occurring in a lower extent under the conditions tested, being responsible for a decrease of the light olefins yield. Finally, the adsorption of phenol molecules instead of polyaromatics in surrounding acid sites increases the formation of branched molecules. Hence, the transformation of the different compounds families constituting conventional FCC feedstocks could be influenced at different levels when co-processed with hydrotreated bio-oils rich in phenolic compounds. In fact, the alkanes cracking should be more negatively affected than the naphthenes cracking, at the low contact times and higher temperatures performed in FCC riser, being the deactivating effect certainly dependent on the quantity of bio-oils incorporated to the FCC feedstocks. Acknowledgments I. Grac¸a thanks the Fundac¸ão para a Ciência e Tecnologia (FCT) for her PhD grant (SFRH/BD/37270/2007) and the project PTDC/QUEERQ/103912/2008. References ˜ [1] J.C. Escobar, E.S. Lora, O.J. Venturini, E.E. Yánez, E.F. Castillo, O. Almazam, Renew. Sustain. Energy Rev. 13 (2009) 1275–1287. [2] J.-P. Lange, Biofuels, Bioprod. Biorefineries 1 (2007) 39–48. [3] T. Bridgwater, Biomass Bioenergy 31 (2007) I–VII. [4] A.V. Bridgwater, Chem. Eng. J. 91 (2003) 87–102. [5] G.W. Huber, S. Iborra, A. Corma, Chem. Rev. 106 (2006) 4044–4098. [6] A. Demirbas¸, Energy Convers. Manage. 41 (2000) 633–646. [7] H.B. Goyal, Diptendu Seal, R.C. Saxena, Renew. Sustain. Energy Rev. 12 (2008) 504–517. [8] L. Qiang, L. Wen-Zhi, Z. Xi-Feng, Energy Convers. Manage. 50 (2009) 1376–1383. [9] Z. Qi, C. Jie, W. Tiejun, X. Ying, Energy Convers. Manage. 48 (2007) 87–92. [10] A. Oasmaa, S. Czernik, Energy Fuels 13 (1999) 914–921. [11] S. Czernik, A.V. Bridgwater, Energy Fuels 18 (2004) 590–598. [12] D. Mohan, C.U. Pittman Jr., P.H. Steele, Energy Fuels 20 (2006) 848–889. [13] P. O’Connor, Stud. Surf. Sci. Catal. 166 (2007) 227–251. [14] Y. Chen, Powder Technol. 163 (2006) 2–8. [15] H.S. Cerqueira, G. Caeiro, L. Costa, F. Ramôa Ribeiro, J. Mol. Catal. A: Chem. 292 (2008) 1–13. [16] R. Sadeghbeigi, Fluid Catalytic Cracking Handbook – Design, Operation and Troubleshooting of FCC Facilities, 2nd edition, Gulf Publishing Company, USA, 2000. [17] A. Corma, A.V. Orchilles, Micropor. Mesopor. Mater. 35/36 (2000) 21–30. [18] M.S. Rigutto, R. Veen, L. Huve, Stud. Surf. Sci. Catal. 168 (2007) 855–913. [19] B.S. Gevert, J.-E. Otterstedt, Biomass 14 (1987) 173–183. [20] M.C. Samolada, W. Baldauf, I.A. Vasalos, Fuel 77 (1998) 1667–1675. [21] A.A. Lappas, S. Bezergianni, I.A. Vasalos, Catal. Today 145 (2009) 55–62. [22] M.E. Domine, A.C. van Veen, Y. Schuurman, C. Mirodatos, ChemSusChem 1 (2008) 179–181. [23] E. Laurent, B. Delmon, Appl. Catal. A: Gen. 109 (1994) 77–96. [24] R. Maggi, B. Delmon, Biomass Bioenergy 7 (1994) 245–249. [25] A.Y. Bunch, X. Wang, U.S. Ozkan, J. Mol. Catal. A: Chem. 270 (2007) 264–272. [26] O.I. Senol, T.-R. Viljava, A.O.I. Krause, Appl. Catal. A: Gen. 326 (2007) 236–244. [27] O.I. Senol, E.-M. Ryymin, T.-R. Viljava, A.O.I. Krause, J. Mol. Catal. A: Chem. 277 (2007) 107–112. [28] I. Grac¸a, J.-D. Comparot, S. Laforge, P. Magnoux, J.M. Lopes, M.F. Ribeiro, F. Ramôa Ribeiro, Appl. Catal. A: Gen. 353 (2009) 123–129. [29] I. Grac¸a, F. Ramôa Ribeiro, H.S. Cerqueira, Y.L. Lam, M.B.B. de Almeida, Appl. Catal. B: Environ. 90 (2009) 556–563. [30] B.W. Wojciechowski, A. Corma, Catalytic Cracking: Catalyst, Chemistry and Kinetics, Marcel Dekker, Inc., New York, 1986. [31] S.J. Gregg, K.S.W. Sing, Adsorption Surface Area and Porosity, 2nd edition, Academic Press, London, 1982. [32] G. Leofanti, M. Padovan, G. Tozzola, B. Venturelli, Catal. Today 41 (1998) 207–219. [33] M. Guisnet, P. Ayrault, J. Datka, Pol. J. Chem. 71 (1997) 1455–1461. [34] D.W. Breck, E.M. Flanigen, Molecular Sieves, Society of Chemical Industry, London, 1968, p. 47. [35] M. Guisnet, P. Magnoux, Appl. Catal. 54 (1989) 1–27.

I. Grac¸a et al. / Applied Catalysis A: General 385 (2010) 178–189 [36] M. Guisnet, P. Magnoux, Appl. Catal. A: Gen. 212 (2001) 83–96. [37] M. Guisnet, P. Magnoux, D. Martin, Stud. Surf. Sci. Catal. 111 (1997) 1–19. [38] I.P. Dzikh, J.M. Lopes, F. Lemos, F. Ramôa Ribeiro, Appl. Catal. A: Gen. 176 (1999) 239–250. [39] J.P. Marques, I. Gener, J.M. Lopes, F. Ramôa Ribeiro, M. Guisnet, Catal. Today 107–108 (2005) 726–733. [40] P. Matias, J.M. Lopes, S. Laforge, P. Magnoux, M. Guisnet, F. Ramôa Ribeiro, Appl. Catal. A: Gen. 351 (2008) 174–183. [41] X. Zhao, R. Harding, Ind. Eng. Chem. Res. 38 (1999) 3854–3859. [42] X. Zhu, S. Liu, Y. Song, L. Xu, Appl. Catal. A: Gen. 288 (2005) 134–142. [43] J.D. Adjaye, N.N. Bakhshi, Biomass Bioenergy 8 (1995) 131–149. [44] H.S. Cerqueira, P. Magnoux, D. Martin, M. Guisnet, Appl. Catal. A: Gen. 208 (2001) 359–367. [45] P.C. Mihindou-Koumba, H.S. Cerqueira, P. Magnoux, M. Guisnet, Ind. Eng. Chem. Res. 40 (2001) 1042–1051. [46] G. Caeiro, J.M. Lopes, P. Magnoux, P. Ayrault, F. Ramôa Ribeiro, J. Catal. 249 (2007) 234–243.

189

[47] G. Caeiro, P. Magnoux, J.M. Lopes, F. Ramôa Ribeiro, Appl. Catal. A: Gen. 292 (2005) 189–199. [48] H.G. Karge, J. Weitkamp (Eds.), Molecular Sieves, Characterization II, vol. 5, Springer, Berlin, 1999. [49] P.E. Eberly Jr., C.N. Kimberlin, W.H. Miller, H.V. Drushel, Ind. Eng. Chem. Process Des. Dev. 5 (1966) 193–198. [50] T. Beutel, J. Chem. Soc., Faraday Trans. 94 (1998) 985–993. [51] E. Selli, A. Isernia, L. Forni, Phys. Chem. Chem. Phys. 2 (2000) 3301–3305. [52] A. Waclaw, K. Nowinska, W. Schwieger, Appl. Catal. A: Gen. 270 (2004) 151– 156. [53] H.S. Cerqueira, P. Ayrault, J. Datka, M. Guisnet, Micropor. Mesopor. Mater. 38 (2000) 197–205. [54] M.A. Makarova, J. Dwyer, J. Phys. Chem. 97 (1993) 6337–6338. [55] S. Morin, P. Ayrault, N.S. Gnep, M. Guisnet, Appl. Catal. A: Gen. 166 (1998) 281–292. [56] A. Zecchina, S. Bordiga, G. Spoto, D. Scarano, G. Petrini, G. Leofanti, M. Padovan, J. Chem. Soc., Faraday Trans. 88 (1992) 2959–2969.